Epidemiological News: Week 47, 2025
Executive Summary
The epidemiological landscape during week 47 of 2025 reveals several notable developments across Bulgaria, the European Union/European Economic Area (EU/EEA), and globally. This surveillance period, which spans 17-23 November 2025, demonstrates the dynamic nature of infectious disease transmission as winter approaches in the Northern Hemisphere.
The most striking development in the EU/EEA region is the unusually early onset of the 2025-2026 influenza season, which has begun three to four weeks earlier than in the previous two years. Influenza A, particularly the A(H3N2) subclade K, is driving rapidly increasing detections across member states, prompting the European Centre for Disease Prevention and Control (ECDC) to publish a Threat Assessment Brief on 20 November 2025. While respiratory illness presentations in primary care remain at baseline or low levels, the accelerating pace of influenza detections and early hospitalization trends, especially among adults aged 65 years and above, warrant heightened attention from public health authorities. Concurrently, respiratory syncytial virus (RSV) circulation is showing slow increases approximately one week later than the previous season, with children under five years predominantly affected.
In Bulgaria, respiratory virus surveillance for week 47 shows relatively stable patterns, though the country is participating in the broader European trend of early influenza activity. The Bulgarian data reveal significant increases in acute viral hepatitis cases, with 86 cases reported during week 47 representing a substantial 47-case increase from the previous week. This surge, which brings the year-to-date total to 1,403 cases compared to 632 cases during the same period in 2024, represents a 771-case or 122% increase year-on-year and merits careful investigation.
Globally, multiple disease surveillance systems are tracking developments ranging from emerging viral hemorrhagic fevers in Africa to the continued evolution of avian influenza viruses with pandemic potential. Ethiopia is experiencing its first-ever documented outbreak of Marburg virus disease, with six confirmed cases and six deaths as of 20 November 2025. The Democratic Republic of the Congo’s Ebola virus disease outbreak in Kasai Province appears to be concluding, with the 42-day countdown to declare the outbreak over having begun on 19 October 2025, following the discharge of the last patient. Meanwhile, West Africa confronts a multi-country Rift Valley fever outbreak affecting Senegal, Mauritania, and The Gambia, with both human cases and extensive livestock involvement.
The first human case of avian influenza A(H5N5) globally has been confirmed in Washington State, United States, marking a significant development in the ongoing global surveillance of highly pathogenic avian influenza. While this case does not appear to carry mammalian adaptation markers of major concern, it underscores the persistent spillover risk from wild bird reservoirs to humans with occupational or incidental exposure to infected poultry.
Non-Communicable Disease Developments
Pharmacovigilance and Medicinal Product Safety
The European Medicines Agency’s Pharmacovigilance Risk Assessment Committee convened its monthly meeting from 24-27 November 2025 in Amsterdam to evaluate the safety profiles of numerous medicinal products authorized in the European Union. This routine but essential activity represents a critical component of the post-authorization surveillance system that protects public health by continuously monitoring the benefit-risk balance of medicines throughout their lifecycle.
The PRAC agenda for this meeting included evaluation of multiple periodic safety update reports (PSURs) for centrally authorized products spanning diverse therapeutic areas. Among the products under review were several high-profile medicines that have been subjects of intensive pharmacovigilance scrutiny. Notably, the Committee evaluated safety data for COVID-19 vaccines, including Kostaive, which submitted updates based on final results from study ARCT-2303-01, a Phase 3 observer-blind, randomized controlled study evaluating the immunogenicity, reactogenicity, and safety of the vaccine when administered concomitantly with quadrivalent influenza vaccines in adults.
Several oncology products received attention during this meeting cycle. The PRAC reviewed signal assessments for axicabtagene ciloleucel (Yescarta), a chimeric antigen receptor (CAR) T-cell therapy used in treating certain B-cell malignancies. A new signal of increased risk of brain edema specifically in primary mediastinal large B-cell lymphoma (PMBCL) patients was evaluated, reflecting the ongoing refinement of safety knowledge for these complex cellular therapies that have revolutionized cancer treatment but carry unique and serious adverse event profiles. The Committee also assessed a signal of cardiotoxicity associated with venlafaxine, a widely used antidepressant, and a signal of congenital megacolon following maternal exposure to ponatinib (Iclusig) during pregnancy, both of which could have important implications for prescribing practices if confirmed.
Risk management plan evaluations formed another substantial component of the meeting, with 15 pre-authorization products undergoing assessment. These included treatments for diverse conditions ranging from African trypanosomiasis (sleeping sickness) with acoziborole to obstructive hypertrophic cardiomyopathy with aficamten, and from Parkinson’s disease with a levodopa/carbidopa combination to WHIM syndrome with mavorixafor. The breadth of therapeutic areas represented underscores the continuous innovation in pharmaceutical development while highlighting the regulatory responsibility to ensure that new medicines entering the market have appropriate risk mitigation measures in place.
Post-authorization safety studies (PASS) constituted a significant portion of the Committee’s workload, with both imposed and non-imposed studies under review. Imposed PASS protocols were evaluated for lecanemab (Leqembi), an Alzheimer’s disease treatment requiring real-world safety monitoring, and obecabtagene autoleucel (Aucatzyl), another CAR T-cell therapy. These imposed studies reflect regulatory requirements placed on marketing authorization holders when residual uncertainties about safety require systematic post-marketing investigation.
The Committee also reviewed interim and final reports from numerous ongoing post-authorization studies. Notably, several studies focused on the long-term safety of advanced therapy medicinal products (ATMPs) such as ciltacabtagene autoleucel (Carvykti) for multiple myeloma and dinutuximab beta (Qarziba) for high-risk neuroblastoma, reflecting the particular importance of extended safety follow-up for these innovative but complex biological therapies whose long-term effects may not be fully characterized during pre-marketing clinical trials.
Infant Botulism Outbreak Associated with Contaminated Infant Formula
A multistate outbreak of infant botulism in the United States emerged as a significant food safety concern in November 2025, linked to contaminated ByHeart Whole Nutrition Infant Formula. As of 19 November 2025, infant botulism was confirmed or suspected in 31 infants across 15 states. All affected infants required hospitalization, though no deaths have been reported. Illness onset dates ranged from 9 August to 13 November 2025, indicating that the contamination problem may have persisted for several months before detection and that the outbreak was identified through astute clinical recognition and public health surveillance rather than through routine product testing.
Infant botulism represents a distinct form of botulism that occurs when infants ingest Clostridium botulinum spores, which then germinate, colonize the intestinal tract, and produce botulinum neurotoxin in vivo. This differs from foodborne botulism in older children and adults, where preformed toxin in contaminated food is ingested. Infants are uniquely susceptible to this colonization form of botulism because their intestinal microbiota are not yet fully developed, allowing C. botulinum spores to germinate and produce toxin within the gut. The disease typically affects infants under one year of age, with peak incidence between two and six months of age.
Clinical presentation of infant botulism characteristically begins with constipation, followed by progressive bilateral descending paralysis. Affected infants may present with lethargy, weak cry, poor feeding, decreased gag reflex, ptosis, and dilated pupils. The paralysis can progress to involve respiratory muscles, necessitating mechanical ventilation in severe cases. The diagnosis requires a high index of clinical suspicion, as early symptoms can be subtle and nonspecific. Confirmation typically involves detection of botulinum toxin and/or C. botulinum organisms in infant stool specimens, though toxin may not always be detectable even in confirmed cases.
Preliminary testing by the California Department of Public Health detected botulinum neurotoxin type A in an open can of ByHeart powdered infant formula (lot 206VABP/251131P2) that had been fed to an infant with laboratory-confirmed infant botulism. Subsequent testing confirmed the presence of Clostridium botulinum through culture. The detection of C. botulinum in infant formula represents a serious quality control failure, as powdered infant formula production processes should prevent such contamination. However, as noted by investigators, detection of C. botulinum in infant formula can be technically challenging, and a negative test result does not definitively rule out the presence of the bacterium, particularly given the low infectious dose (as few as 10-100 spores may be sufficient to cause disease in susceptible infants).
The U.S. Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) launched a comprehensive investigation in collaboration with state and local health authorities. FDA inspections and sampling of unopened product containers continued as of late November, with investigations aimed at determining the source of contamination within the production process. All lots and sizes of ByHeart Whole Nutrition Infant Formula, including both cans and single-serve packets, have been recalled and withdrawn from stores and online retailers. Products were also sold online to international customers, raising concerns about exposure beyond the United States.
From a European perspective, the risk assessment conducted by ECDC concluded that based on currently available information, the product is not known to be sold on the European market through official distribution channels. However, the possibility of individual consumers having purchased the product through online platforms cannot be entirely excluded. Consequently, the risk in the EU/EEA of infant botulism associated with this product is considered restricted to individual consumers who may have bought the product online. Control measures implemented in the United States and by major online platforms should significantly reduce the likelihood of continued exposure to contaminated products, though complete elimination of risk requires ongoing vigilance.
This outbreak highlights several important public health principles. First, it demonstrates the critical importance of robust food safety systems and quality control in infant formula production, given the particular vulnerability of this population. Second, it underscores the value of clinical acumen and disease surveillance systems in detecting outbreaks, as this event was identified through recognition of a cluster of cases rather than through routine product testing. Third, it illustrates the challenges of controlling distribution of contaminated products in the era of global e-commerce, where products recalled in one jurisdiction may still be accessible to consumers elsewhere through online purchasing. Finally, it emphasizes the need for international coordination and information sharing in food safety incidents with potential cross-border implications.
Infectious Diseases: Global Perspective
Respiratory and Droplet Transmission
Influenza A(H5N1) - Continued Spillover from Avian Reservoirs
Global surveillance of highly pathogenic avian influenza continues to document sporadic human cases resulting from direct contact with infected poultry or contaminated environments. On 16 November 2025, Cambodia reported a fatal human case of avian influenza A(H5N1) virus infection in an adult man from Chroy Changvar District in the autonomous municipality of Phnom Penh. The patient developed symptoms including fever, cough, fatigue, and difficulty breathing. Despite receiving medical care, he succumbed to the infection on 15 November 2025, the same day that the National Institute of Public Health confirmed infection with avian influenza A(H5N1) through laboratory testing.
This case represents Cambodia’s 18th human A(H5N1) infection in 2025, bringing the country’s cumulative total since the disease first emerged there to 90 cases, including 52 deaths, yielding a case fatality rate of 58%. This extraordinarily high case fatality rate reflects both the inherent virulence of A(H5N1) viruses in humans and potential ascertainment bias, as mild or subclinical infections are less likely to come to medical attention and be diagnosed. Cambodia’s continued experience with human A(H5N1) cases reflects persistent circulation of the virus in poultry populations and ongoing human-avian interfaces that create opportunities for zoonotic transmission.
The clinical presentation described for the Cambodian case is consistent with the typical progression of severe A(H5N1) infection in humans. Following an incubation period typically ranging from two to five days (though occasionally longer), patients usually present with high fever and respiratory symptoms. Unlike seasonal influenza, which primarily affects the upper respiratory tract, avian influenza A(H5N1) has tropism for lower respiratory epithelium, leading to severe pneumonia and acute respiratory distress syndrome (ARDS). Many patients develop multi-organ failure, including hepatic dysfunction, renal impairment, and encephalopathy. The rapid progression from symptom onset to critical illness and death is characteristic of severe A(H5N1) infections.
Virological surveillance indicates that circulating A(H5N1) viruses retain genetic characteristics consistent with avian-adapted influenza viruses, lacking most of the specific mutations known to facilitate efficient mammalian adaptation and human-to-human transmission. This is a critical observation from a pandemic preparedness perspective. The key barriers to pandemic emergence include inefficient transmission from birds to humans (requiring direct contact with infected birds or heavily contaminated environments), lack of sustained human-to-human transmission, and retention of receptor-binding preferences for avian-type receptors rather than human-type receptors in the respiratory tract.
Despite these reassuring virological features, the persistent global circulation of A(H5N1) in poultry and wild birds, combined with the virus’s demonstrated ability to cause severe and often fatal disease in humans, necessitates continued vigilance. Each human infection represents not only a personal tragedy but also an opportunity for the virus to adapt to mammalian hosts. While the risk of a specific human case leading to pandemic emergence remains very low, the cumulative risk over time and across multiple exposures cannot be dismissed.
National and local authorities in Cambodia are implementing response measures including active contact tracing, antiviral prophylaxis (Tamiflu) for close contacts of the case, and health education campaigns in affected villages. These interventions aim to identify any potential secondary cases quickly (which would represent a worrying signal of improving human-to-human transmission capability) and to reduce further zoonotic exposures through behavior change.
Since 2003, when enhanced global surveillance for human A(H5N1) infections began, a cumulative total of 993 confirmed human cases have been reported worldwide as of 17 November 2025, including 476 deaths, yielding an overall case fatality rate of 48%. These cases have been reported from 25 countries across Asia, Europe, Africa, and North America, though the geographic distribution is highly skewed, with most cases occurring in Egypt, Indonesia, Vietnam, and Cambodia. The absence of sustained human-to-human transmission across this 22-year surveillance period, despite nearly 1,000 human infections, provides some reassurance that the genetic barriers to pandemic emergence are substantial. However, it also underscores that these barriers are not absolute, and continued spillover events maintain pandemic risk.
Influenza A(H5N5) - First Human Case Globally
On 14 November 2025, the Washington State Department of Health reported the first confirmed human infection globally with avian influenza A(H5N5) virus. This novel finding represents an important development in avian influenza surveillance and underscores the ongoing spillover risk from diverse avian influenza subtypes circulating in wild bird and poultry populations.
The case involved an older adult resident of Grays Harbor County, Washington, with underlying health conditions. The patient was hospitalized in early November 2025 and remained under medical care at the time of reporting. Epidemiological investigation identified the likely source of exposure as a mixed backyard flock of domestic poultry that had contact with wild birds. This exposure pattern is typical for avian influenza spillover events, where the interface between wild bird reservoirs, domestic poultry, and humans creates opportunities for zoonotic transmission. Backyard poultry production, while often undertaken for personal food security or hobby purposes, can create biosecurity vulnerabilities when birds have outdoor access and potential contact with wild bird populations.
The genetic characterization of the virus isolated from this case provided important virological insights. Sequencing revealed that the isolate (designated A/Washington/2148/2025) belongs to clade 2.3.4.4b, genotype A6, which has been commonly reported for recent A(H5N5) detections in birds and mammals in North America. In European nomenclature, this genotype is referred to as EA-2021-I. The hemagglutinin (HA) segment of the virus clusters closely with other clade 2.3.4.4b strains of the same subtype but is distinct from the A(H5N1) genotypes B3.13 and D1.1 that include strains associated with recent human infections in the United States related to the dairy cattle outbreak.
Critically, the A/Washington/2148/2025 virus does not contain key mutations associated with mammalian adaptation of pandemic concern. Specifically, the virus lacks markers in the polymerase basic protein 2 (PB2) segment that have been associated with enhanced replication in mammalian hosts. Some European A(H5N5) viruses belonging to genotype EA-2021-I detected in 2025 have contained PB2-E627K or PB2-E627V substitutions, both of which are recognized as mammalian adaptation markers that can enhance virulence and replication efficiency in mammals. However, these concerning markers were absent from the Washington isolate, suggesting this particular virus retains characteristics of an avian-adapted virus with limited mammalian adaptation.
Highly pathogenic avian influenza A(H5N5) of clade 2.3.4.4b has been circulating in wild birds in northern Europe and North America, with the geographic and species range expanding in recent years. The virus has caused spillover infections to wild mammals, domestic birds, and occasionally domestic cats, demonstrating its ability to cross species barriers under appropriate exposure conditions. In Europe during the 2024-2025 epidemiological year, seven EU/EEA countries (Belgium, Estonia, Finland, Germany, Iceland, Norway, and Sweden) reported detections of HPAI A(H5N5) in wild birds, while Iceland and Norway also reported outbreaks in domestic poultry flocks.
Detections in wild mammals have included Arctic and red foxes, lynx, otters, American mink, bobcats, skunks, grey seals, raccoons, and pine martens across Iceland, Norway, the Netherlands, and Canada. The detection in domestic cats in Iceland is particularly noteworthy, as cats can serve as sentinel species for environmental contamination with avian influenza viruses and can potentially transmit infection to humans through close contact, though such transmission appears to be rare.
In North America, Canada reported eight detections of HPAI A(H5N5) in wild birds and one outbreak in domestic poultry during the past epidemiological year, along with detections in the wild mammals noted above. The United States has documented 11 detections in wild birds since the beginning of 2025 according to USDA reports. This widespread circulation in wild bird populations creates ongoing spillover risk to both animals and humans with appropriate exposures.
From a pandemic risk assessment perspective, the first human case of A(H5N5) warrants careful monitoring but does not fundamentally alter the overall assessment of risk from avian influenza viruses. The U.S. CDC maintains its assessment that the risk of avian influenza A(H5) to the general public remains low. This assessment is based on several factors: the absence of sustained human-to-human transmission of any avian influenza A(H5) subtype despite decades of surveillance, the requirement for direct contact with infected birds or heavily contaminated environments for human infection to occur, and the virological characteristics of circulating viruses that remain primarily adapted to avian hosts.
However, the detection of this first human A(H5N5) case globally does highlight several important points. First, it demonstrates that multiple subtypes of highly pathogenic avian influenza (not just A(H5N1)) pose zoonotic risk to humans with appropriate exposures. Second, it underscores the importance of biosecurity measures for backyard poultry producers, including preventing contact between domestic birds and wild birds, using personal protective equipment when handling birds or cleaning coops, and promptly reporting sick or dead birds to veterinary authorities. Third, it emphasizes the need for continued surveillance and characterization of avian influenza viruses in both animal and human populations to detect emerging variants of concern rapidly.
For the European context, where A(H5N5) viruses have been circulating in wild birds and causing occasional mammalian spillovers, this first human case serves as a reminder that the spillover risk applies across regions where the virus is present. Healthcare providers in areas with documented A(H5N5) circulation should maintain awareness of avian influenza as a differential diagnosis in patients presenting with severe respiratory illness who have recent exposure to poultry or wild birds. Early recognition and appropriate infection control measures can prevent nosocomial transmission, which has occurred rarely with avian influenza but represents a potential risk in healthcare settings.
Vector-Borne Transmission
Rift Valley Fever - West African Multi-Country Outbreak
West Africa is experiencing a significant multi-country outbreak of Rift Valley fever (RVF) affecting human and animal populations in Senegal, Mauritania, and The Gambia. This outbreak, which emerged in late September 2025, represents an important public health event given RVF’s potential for severe disease in humans, its impact on livestock economies, and the risk of geographic expansion.
Rift Valley fever is an acute viral disease caused by RVF virus, a member of the genus Phlebovirus in the family Phenuiviridae. The virus is primarily maintained in nature through a complex transmission cycle involving Aedes mosquito species and various vertebrate hosts, particularly domestic ruminants such as cattle, sheep, and goats. The disease derives its name from the Rift Valley of Kenya where it was first identified in 1931 during an investigation into an epizootic among sheep. While endemic to sub-Saharan Africa, the disease has demonstrated capacity for expansion, with major outbreaks documented in Egypt (1977-78), Saudi Arabia and Yemen (2000), and more recently in Madagascar and other locations.
As of 20 November 2025, Senegal has reported 482 human cases including 31 deaths, yielding a case fatality rate of 6.4%. The outbreak began on 21 September 2025, with 419 patients having recovered and one person hospitalized at the time of reporting. According to Africa CDC, most cases occurred in males, and the most affected age group is individuals aged 15-35 years, likely reflecting occupational exposure patterns related to livestock husbandry and slaughtering activities. The geographic distribution spans 11 regions: Saint-Louis (344 cases), Louga (21), Matam (34), Fatick (32), Dakar (13), Kaolack (24), Thiès (2), Tambacounda (5), Kèdougou (2), Kaffrine (2), and Kolda (1). Many of these affected regions are in the northern part of the country, particularly around the Senegal River valley and delta, bordering Mauritania. Notably, cases have recently begun spreading to southern parts of the country, raising concerns about potential cross-border transmission to The Gambia, Mali, Guinea, and Guinea-Bissau.
The livestock component of the outbreak in Senegal has been substantial, with 390 cases reported among animals and 1,997 animal abortions documented. The World Organisation for Animal Health (WOAH) reported on 30 September 2025 that the area is at high risk for outbreaks in domestic and wild animals during the winter period, citing notable previous outbreaks in 2013 and 2023. As of 20 November, 29,980 animals have been vaccinated as part of outbreak control efforts. The occurrence of widespread abortion storms in livestock is characteristic of RVF epizootics and often precedes or accompanies human cases, as abortions generate infectious materials that create exposure opportunities for herders, veterinarians, and those handling carcasses.
Mauritania reported its first human cases of this outbreak on 2 October 2025. As of 9 November 2025, the country has documented 52 human cases and 15 deaths, yielding a substantially higher case fatality rate of 28.8% compared to Senegal. The 13 affected regions are concentrated in the southern part of the country near the border with Senegal, with three regions sharing international borders: Assaba (bordering Mali to the south), and Brakna and Trarza (both bordering Senegal along the Senegal River). According to WHO reporting, as of 30 October 2025, there have been 235 confirmed cases and 71 deaths among animals in southern Mauritania since the first outbreak was recorded on 15 September 2025.
The Gambia reported its first human case of RVF on 5 November 2025, according to media reports citing health officials. The case occurred in the Senegalese border village of Ker Ayib. On 28 October 2025, WOAH reported four cases in livestock in The Gambia, confirming the presence of the virus in the country’s animal populations.
The concentration of both human and animal cases around the Senegal River delta and valley is epidemiologically significant. The early autumn months are considered a high-risk period for RVF in this region due to climatic and ecological factors that favor mosquito breeding and viral transmission. Heavy rainfall creates extensive temporary pools and flooded areas that serve as mosquito breeding sites, particularly for Aedes species that can serve as both biological and mechanical vectors for RVF virus. Additionally, the movement of livestock in search of grazing and water during seasonal transhumance patterns may facilitate geographic spread of the virus.
Genomic analysis of viruses from the current outbreak suggests linkage to previous RVF detections in Senegal (Fatick in 2020 and Matam in 2022) and in Mauritania (2020), indicating that the virus has been circulating at low levels in the region for several years and has now emerged in epidemic form under favorable conditions. This pattern of endemic maintenance with periodic epidemic emergence is characteristic of RVF epidemiology in endemic regions.
Human infection with RVF virus occurs through multiple exposure routes. Direct contact with blood, body fluids, or tissues of infected animals during slaughtering, butchering, or assisting with animal births is the most common route, particularly for adults with occupational exposure. Consumption of raw or undercooked meat or unpasteurized milk from infected animals can also result in transmission, though this is less common. Mosquito-borne transmission can occur but is believed to play a smaller role in human infection compared to direct animal contact. Human-to-human transmission has not been documented, though theoretical risk exists through contact with blood or body fluids of severely ill patients, particularly in healthcare settings.
The clinical spectrum of RVF in humans ranges from asymptomatic or mild febrile illness to severe disease with potentially fatal complications. Most infected individuals experience a relatively mild illness characterized by abrupt onset of fever, headache, myalgias, and sometimes gastrointestinal symptoms, with spontaneous recovery occurring within a few days to a week. However, a small percentage of patients (estimated at 1-2%) develop much more severe forms of disease. These severe manifestations include ocular disease (retinitis that can lead to permanent vision loss), hemorrhagic fever (with hepatitis, hemorrhagic diathesis, and multi-organ failure), and encephalitis. The case fatality rate among patients developing hemorrhagic manifestations can exceed 50%, accounting for the overall case fatality rates observed in this outbreak.
From a European public health perspective, ECDC’s risk assessment concludes that travelers to and residents of Senegal or Mauritania are at low risk of infection if they apply appropriate preventive measures. Those in contact with potentially infected animals (veterinarians, livestock farmers, abattoir workers, and those involved in butchering and slaughtering in RVF-affected areas) face increased risk and should ensure safe animal husbandry and slaughtering practices, including use of personal protective equipment. Visitors to affected areas should apply personal protective measures against mosquito bites, including use of repellents, protective clothing, and avoiding outdoor activities during peak mosquito activity periods.
The likelihood of RVF virus being introduced into EU/EEA countries is assessed as very low, as importation of live ruminants and raw animal products from affected countries is not permitted under EU veterinary regulations. Importation via travelers is also unlikely, though not impossible, as most human cases resolve quickly and viremia is typically short-lived. The potential for introduction via infected mosquitoes in aircraft or other conveyances is theoretically possible but extremely rare and has not been documented for RVF.
Should the virus be introduced into mainland EU/EEA countries, further vector-borne transmission among animals or humans cannot be excluded but is considered to have very low likelihood during the late autumn and winter season due to low numbers of competent mosquito vectors and low levels of vector activity. The establishment of RVF in European mosquito and livestock populations would require specific conditions that are not currently present.
Transmission of RVF virus through substances of human origin (blood, tissues, organs) has not been reported to date, but the possibility cannot be excluded entirely. However, given that both Senegal, Mauritania, and The Gambia are countries endemic for malaria, the standard deferral period for blood donors returning from malaria-endemic areas would effectively mitigate any potential risk of RVF virus transmission through transfusion, as the deferral period exceeds the typical duration of RVF viremia.
This multi-country outbreak highlights several important principles in emerging infectious disease management. First, it demonstrates the interconnection between animal and human health (the One Health paradigm), as the outbreak in livestock populations directly drives human cases. Effective outbreak control therefore requires coordinated veterinary and public health responses, including animal vaccination campaigns, safe livestock handling practices, and mosquito control measures. Second, it underscores the importance of cross-border collaboration and information sharing in outbreak response, as the affected countries share porous borders, common ecosystems, and transboundary animal movement patterns. Third, it illustrates how climatic and ecological factors can precipitate emergence of previously endemic pathogens into epidemic form, a pattern likely to become increasingly common with ongoing environmental change.
West Nile Virus - European Season Concluding
The 2025 West Nile virus (WNV) transmission season in Europe is winding down as temperatures decrease and vector activity declines with the approach of winter. Since the beginning of 2025 and as of 19 November 2025, 14 countries in Europe have reported human cases of West Nile virus infection: Albania, Bulgaria, Croatia, France, Germany, Greece, Hungary, Italy, Kosovo, North Macedonia, Romania, Serbia, Spain, and Türkiye. A total of 156 areas are currently known to be affected, reflecting the widespread distribution of WNV circulation across southern and central Europe during the 2025 transmission season.
West Nile virus is a mosquito-borne flavivirus maintained in nature through transmission cycles involving Culex mosquito vectors and avian reservoir hosts, particularly corvids and other passerine birds. The virus was historically endemic to Africa, the Middle East, and parts of Asia but has expanded its geographic range dramatically over recent decades, with establishment in southern Europe in the 1990s and introduction to North America in 1999. European WNV transmission typically occurs during the warmer months (roughly June through November) when mosquito populations are active, with peak transmission often observed in August and September.
Most human WNV infections (approximately 80%) are asymptomatic. Among those who develop symptoms, the majority experience West Nile fever, a self-limited febrile illness characterized by abrupt onset of fever, headache, myalgia, sometimes with rash, lymphadenopathy, and gastrointestinal symptoms. This uncomplicated form typically resolves within a few days to weeks without specific treatment. However, approximately 1% of infected individuals develop neuroinvasive disease, which can manifest as meningitis, encephalitis, or acute flaccid paralysis. Neuroinvasive WNV disease carries significant morbidity and mortality, with case fatality rates ranging from 3-15%, and long-term neurological sequelae common among survivors.
Risk factors for neuroinvasive disease include advanced age (particularly over 60 years), immunosuppression, and certain chronic medical conditions such as diabetes mellitus, hypertension, and chronic renal disease. The pathogenesis of neuroinvasive disease involves viral invasion of the central nervous system, likely through hematogenous dissemination followed by crossing of the blood-brain barrier, though the precise mechanisms remain incompletely understood.
No specific antiviral therapy exists for WNV infection, and management is supportive, focusing on maintenance of hydration, management of neurological complications, and prevention of secondary complications. Similarly, no vaccine is licensed for human use (though equine vaccines exist), making prevention of mosquito exposure the primary intervention available. Public health measures during WNV transmission seasons include mosquito control activities (larviciding and adulticiding in some jurisdictions), public education campaigns about mosquito avoidance, and surveillance systems to detect viral circulation in mosquitoes, birds, and humans.
The seasonal pattern of WNV transmission means that as November progresses and winter approaches in Europe, new human cases become increasingly unlikely due to reduced mosquito activity and cessation of outdoor human-mosquito contact. The surveillance data reported for week 47 therefore likely represent late-season cases or delayed reporting of earlier infections rather than indication of ongoing high-level transmission. However, given climate variability and the potential for extended periods of warm weather, surveillance authorities maintain vigilance throughout the traditional risk period.
From a public health perspective, the 2025 WNV season in Europe appears to have followed patterns generally consistent with recent years, though detailed comparative analysis would require review of weekly surveillance trends throughout the season. The geographic distribution encompassing 14 countries across southeastern, central, and southern Europe reflects the established distribution of WNV in the region and the widespread presence of competent Culex mosquito vectors. The involvement of 156 specific affected areas indicates localized transmission in multiple regions rather than a few major outbreak epicenters.
As the season concludes, public health priorities shift from immediate case detection and mosquito control to post-season analysis and preparation for subsequent transmission years. This includes characterization of circulating viral lineages through genomic sequencing, assessment of intervention effectiveness, identification of new geographic areas of transmission, and evaluation of surveillance system performance. These activities inform risk assessments and preparedness planning for the following year’s transmission season.
Fecal-Oral Transmission
Infant Botulism - United States Multistate Outbreak
[This section was covered in detail under Non-Communicable Disease Developments due to its product safety aspects, but the outbreak also merits attention as an infectious disease event characterized by fecal-oral transmission of Clostridium botulinum spores. The key points regarding transmission, pathogenesis, clinical features, and public health response are as detailed in that earlier section.]
Contact and Healthcare-Associated Transmission
Marburg Virus Disease - Ethiopia’s First Outbreak
Ethiopia is experiencing its first documented outbreak of Marburg virus disease (MVD), a severe viral hemorrhagic fever with epidemic potential. The outbreak was officially confirmed on 14 November 2025 by the Ethiopian Ministry of Health, following investigation of a suspected event that began in Jinka city on 12 November 2025. As of 20 November 2025, six confirmed cases of MVD have been reported, with a total of six deaths—three among laboratory-confirmed cases and three among suspected cases. Media reports indicate that the deaths include two healthcare workers, highlighting the nosocomial transmission risk that characterizes filovirus outbreaks. Three cases are being treated, and 33 suspected cases are under investigation.
As of 17 November 2025, 129 contacts were being monitored according to the Ethiopian Ministry of Health’s press release. Cases have presented with characteristic symptoms including sudden fever, muscle pain, severe fatigue, headache, diarrhea, vomiting, and in later stages, unexplained bleeding manifestations. Jinka, the epicenter of this outbreak, is a small market town of approximately 30,000 inhabitants located in southwestern Ethiopia, close to the borders with South Sudan and Kenya. It serves as the capital of South Omo region and functions as a tourist hub for the area, though it is approximately two days’ travel from Addis Ababa. A small airport recently inaugurated in Jinka may facilitate both response efforts and potentially raise concerns about risk of disease exportation, though the latter risk remains very low given the clinical severity of MVD and the limited mobility of severely ill patients.
Marburg virus disease is caused by Marburg marburgvirus (MARV), a member of the family Filoviridae that also includes the Ebola viruses. The disease was first recognized in 1967 following simultaneous outbreaks among laboratory workers in Marburg and Frankfurt, Germany, and Belgrade, Yugoslavia (now Serbia), who had been exposed to infected African green monkeys imported from Uganda. This outbreak established MVD as a distinct clinical entity and identified its zoonotic origin in African wildlife.
The natural reservoir of Marburg virus is the Egyptian rousette fruit bat (Rousettus aegyptiacus), which is widely distributed across Africa. The virus circulates in these bat populations without causing apparent disease. Human infection typically occurs through prolonged exposure in mines or caves inhabited by Rousettus bat colonies, where aerosolized virus from bat excreta or direct contact with bats may result in spillover infection. Once introduced into human populations, MVD spreads through direct contact with blood, secretions, organs, or other body fluids of infected persons, and with surfaces and materials (e.g., bedding, clothing) contaminated with these fluids. Healthcare-associated transmission has been a prominent feature of many MVD outbreaks, occurring when infection prevention and control measures are inadequate.
The clinical progression of MVD follows a pattern common to viral hemorrhagic fevers. Following an incubation period typically of five to ten days (range 3-21 days), illness begins abruptly with fever, severe headache, malaise, myalgia, and often gastrointestinal symptoms including watery diarrhea, abdominal pain, and nausea. By day five of illness, many patients develop hemorrhagic manifestations, which can include bleeding from venipuncture sites, gastrointestinal bleeding, hematemesis, bleeding from mucous membranes, and internal hemorrhaging. Neurological symptoms including confusion, agitation, and in severe cases, seizures and coma, may develop. Multi-organ failure, severe bleeding, and shock characterize the terminal phase of illness in fatal cases. Case fatality rates for MVD have ranged from 23% to 88% in previous outbreaks, varying based on viral strain, outbreak context, and availability of supportive care.
Diagnosis requires specialized laboratory testing, as clinical presentation alone cannot reliably distinguish MVD from other causes of viral hemorrhagic fever or even from some other severe infectious diseases such as malaria or typhoid fever in the early stages. Definitive diagnosis relies on detection of viral RNA through reverse transcription polymerase chain reaction (RT-PCR), detection of viral antigens, or isolation of virus from clinical specimens. These tests require biosafety level 4 (BSL-4) containment or appropriate field laboratories with adequate biocontainment, as Marburg virus is classified as a Risk Group 4 pathogen.
No specific antiviral treatment has been approved for MVD, though several investigational therapeutics have shown promise in animal models and may be considered for compassionate use during outbreaks. Treatment is primarily supportive, focusing on maintenance of fluid and electrolyte balance, blood pressure support, replacement of blood and clotting factors, management of secondary infections, and provision of respiratory support when needed. Early aggressive supportive care can significantly improve survival, as demonstrated in recent outbreaks where case fatality rates were substantially lower than historical averages when patients received intensive supportive therapy.
Similarly, no licensed vaccine exists for MVD, though several vaccine candidates are in development based on platforms similar to those used for Ebola vaccines. This absence of specific therapeutics and vaccines makes outbreak control heavily dependent on non-pharmaceutical interventions including case identification and isolation, contact tracing and monitoring, infection prevention and control in healthcare settings, safe and dignified burial practices, and community engagement to promote risk reduction behaviors.
The Ethiopian outbreak represents only the 11th country globally to document MVD cases since the disease was first identified in 1967. Previous outbreak countries include Angola, Democratic Republic of the Congo, Ghana, Guinea, Equatorial Guinea, Kenya, South Africa, Tanzania, Uganda, and most recently Rwanda, which experienced its first outbreak in 2024 (66 cases including 15 deaths) before declaring the outbreak over on 20 December 2024. Tanzania reported its second MVD outbreak in 2025 (two confirmed and eight probable cases, all fatal). The cumulative documented global total of MVD cases across all outbreaks since 1967 approximates 600, making it a rare disease compared to many other infectious diseases, though its severity and epidemic potential make it a high-consequence pathogen requiring robust surveillance and preparedness.
Whole genome sequencing analysis conducted on Ethiopian isolates indicates similarity to viral strains previously identified in East Africa, suggesting this outbreak resulted from a spillover event from the regional bat reservoir rather than importation from a distant geographic location. This finding is consistent with the known distribution of Egyptian rousette bats in the region and with previous patterns of MVD emergence in East Africa.
The response to the outbreak involves multiple partners coordinating with the Ethiopian Ministry of Health. Community-level monitoring, contact tracing, and house-to-house case finding have been intensified. Infection prevention and control measures are being strengthened in healthcare facilities. Vaccination of healthcare workers and other high-risk contacts may be considered using investigational vaccines under emergency use protocols if circumstances warrant and if vaccine supplies can be accessed. Risk communication and community engagement efforts aim to promote early care-seeking, safe burial practices, and risk reduction behaviors while combating stigma and misinformation.
From a European public health perspective, ECDC’s risk assessment for this outbreak provides several conclusions. The likelihood of exposure to MVD for EU/EEA citizens visiting or living in Ethiopia is assessed as low, with uncertainties connected to the limited epidemiological information available at this early stage of the outbreak. The impact, assessed at population level, is low since the number of MVD cases expected among EU/EEA citizens in Ethiopia is very small. Therefore, the overall risk for EU/EEA citizens visiting or living in Ethiopia is assessed as low.
In the event that MVD cases are imported into the EU/EEA—for example, through an infected person traveling during the incubation period or early symptomatic phase—ECDC considers the likelihood of further transmission to be very low, and the associated impact low. Consequently, the overall risk for the EU/EEA is assessed as low. This assessment is based on several factors: the clinical severity of MVD means most patients are too ill to travel once symptoms are advanced; the well-developed healthcare systems and infection prevention and control capacity in EU/EEA countries are capable of safely isolating and managing viral hemorrhagic fever cases; and the limited opportunities for disease transmission in European settings compared to the circumstances present in outbreak settings in endemic countries.
Nevertheless, healthcare systems in EU/EEA countries maintain preparedness for potential importation of viral hemorrhagic fevers including MVD. This preparedness includes protocols for assessment of febrile travelers from affected areas, designated high-level isolation units capable of managing highly infectious diseases, trained healthcare personnel with appropriate personal protective equipment, and laboratory diagnostic capacity for rapid confirmation of cases. Healthcare providers should maintain awareness of MVD as a differential diagnosis in travelers from affected areas of Ethiopia who present with compatible symptoms, particularly if there is known exposure to caves, mines, or bat-inhabited areas, or contact with sick persons.
Ebola Virus Disease - Democratic Republic of the Congo
The Ebola virus disease outbreak in Kasai Province, Democratic Republic of the Congo (DRC), which was declared on 4 September 2025, appears to be reaching its conclusion. On 19 October 2025, WHO announced that the last Ebola patient in the DRC was discharged, initiating the 42-day countdown for declaring the outbreak over. A total of 19 patients have recovered from the disease (29.7% of all cases), and no new cases have been reported since 26 September 2025. As of 20 November 2025, of the 1,735 contacts (out of 1,787, or 97.3%) that were followed up, none remain under active monitoring.
Since the outbreak was declared, and as of 20 November, there have been 64 cases (53 confirmed and 11 probable) and 45 deaths (34 confirmed and 11 probable), yielding an overall case fatality rate of 70.3%. All cases were reported from six health areas in Bulape health zone, Kasai Province, with the health areas of Dikolo (26 cases, 15 deaths) and Bulape (24 cases, 22 deaths) serving as the epicenters, together accounting for 78.1% of reported cases and 82.2% of all deaths.
The epidemiological and clinical characteristics of this outbreak provide important insights. Based on whole genome sequencing analysis, the causative strain is not linked to previous outbreaks in the DRC, indicating this represents a new zoonotic spillover event rather than resurgence from a persistent infection or continuation of a previous outbreak chain. This finding has implications for understanding Ebola virus ecology and spillover dynamics. The initial phase of the outbreak was characterized by nosocomial spread and a superspreading event linked to the presumptive index case’s funeral, highlighting the critical importance of safe and dignified burial practices and robust infection prevention and control in healthcare settings.
The presumptive index case was a pregnant woman admitted to Bulape General Reference Hospital on 20 August 2025 with symptoms including fever, bloody diarrhea, vomiting, asthenia, and hemorrhagic manifestations (anal, oral, and nasal hemorrhage). She subsequently died due to multiple organ failure. Samples tested on 3 September at the country’s National Institute of Biomedical Research in Kinshasa confirmed Zaire ebolavirus as the causative agent.
The demographic and age distribution of cases showed notable patterns. On 28 September, WHO reported that 37 cases (57.8%) occurred in women, with patients’ ages ranging from under one year to 65 years. Children aged from under one year to nine years and individuals aged 20-29 years accounted for 25.0% (16 cases) and 23.4% (15 cases) of the total, respectively. The most affected populations included children, housekeepers, and farmers—groups likely to have had contact with the index case, her contacts, or contaminated environments. Four deaths occurred among healthcare workers, underscoring the occupational risk faced by those caring for Ebola patients.
The temporal dynamics of the outbreak showed evolution over the four-week period from epidemiological week 36 to week 39. The median time between symptom onset and isolation shortened from five days to two days, reflecting improving surveillance sensitivity, faster case detection, and more rapid isolation of cases. This improvement is critical for outbreak control, as each day an infectious person remains in the community represents opportunities for disease transmission. At the outbreak’s onset, a high proportion of cases and deaths occurred among children aged under one year to four years, and the case fatality rate was very high. As the outbreak progressed, the number of cases among children decreased, and the overall case fatality rate gradually declined, likely reflecting both improved clinical management and exhaustion of susceptible contacts in the initial transmission chains.
Women represented 60% of reported deaths, possibly reflecting their roles as primary caregivers for sick family members and their presence at the funeral of the index case. This gender disparity in mortality is consistent with patterns observed in some previous Ebola outbreaks, where cultural practices related to care for the sick and burial of the dead disproportionately expose women to infection risk.
The outbreak response mobilized rapidly following confirmation. Vaccination began in Kasai Province on 13 September using the rVSV-ZEBOV vaccine, which has demonstrated efficacy in outbreak settings. As of 16 November, a total of 44,453 people have been vaccinated using a combination of ring vaccination (targeting contacts and contacts of contacts) and geographically targeted vaccination for high-risk groups in hotspots reporting confirmed cases. Ring vaccination, which involves vaccinating a “ring” of people around each confirmed case, has proven highly effective in controlling Ebola outbreaks by creating a buffer of immunity that prevents further transmission. Geographically targeted vaccination extends protection more broadly in affected areas.
A total of 31 patients received treatment with monoclonal antibody mAb114, one of the therapeutic options available for Ebola virus disease that has shown efficacy in clinical trials. The availability and deployment of both vaccines and therapeutics represent major advances in Ebola outbreak response compared to historical outbreaks, though challenges in access, logistics, and healthcare system capacity remain, particularly in remote areas.
The date of symptom onset for the last reported case was 23 September, with the last cases reported on 26 September in Bulape and Dikolo health areas of Bulape health zone. The epidemiological significance of the 42-day countdown, which began on 19 October following discharge of the last patient, derives from the maximum incubation period of Ebola virus disease (21 days) multiplied by two to account for the possibility of a missed chain of transmission. If 42 days pass without new cases emerging, authorities can have reasonable confidence that active transmission has ceased, though vigilance for possible resurgence remains important, as viral persistence in immune-privileged sites of survivors can occasionally lead to relapse or transmission months or even years after apparent recovery.
This outbreak represents the 16th recorded in the DRC since 1976 when Ebola virus was first identified in the country (then known as Zaire), and the eighth since 2018. The frequency of outbreaks in recent years reflects several factors: the presence of Ebola virus in wildlife reservoirs (primarily fruit bats) in extensive forested areas of the country, ongoing human-wildlife interfaces that create spillover opportunities, movement of populations for various reasons that can spread infection geographically, and perhaps improved surveillance capacity that detects outbreaks that might previously have gone unrecognized.
The DRC’s previous experience with multiple Ebola outbreaks has generated substantial institutional knowledge and response capacity. However, challenges persist including the vast geographic area, limited infrastructure, insecurity in some regions, and resource constraints. The relatively modest size of this outbreak (64 cases) compared to some previous outbreaks in the DRC (particularly the 2018-2020 North Kivu/Ituri outbreak with over 3,400 cases and the 1976 Yambuku outbreak with 318 cases) likely reflects combination of factors including rapid response, availability of vaccines and therapeutics, experience from previous outbreaks, and perhaps fortuitous factors such as outbreak location in a relatively accessible area and absence of major security challenges.
From a broader public health perspective, Ebola outbreaks in the DRC will likely continue to occur periodically given the ecological presence of the virus, making sustained investment in preparedness, surveillance, laboratory capacity, and rapid response capabilities essential. The successful control of this outbreak provides encouragement that with appropriate tools, timely response, and community engagement, even this devastating disease can be controlled, though complacency would be unwarranted given the ongoing risk of future spillover events.
Infectious Diseases: European Union and European Economic Area
Respiratory and Droplet Transmission
Influenza - Unusually Early Seasonal Onset with A(H3N2) Subclade K Dominance
The 2025-2026 influenza season in the EU/EEA has commenced three to four weeks earlier than in the previous two years, marking a notable deviation from recent seasonal patterns. As documented in the European Respiratory Virus Surveillance Summary (ERVISS) for week 47, influenza detections are increasing rapidly across the region despite respiratory illness presentation rates in primary care generally remaining at baseline or low levels. This discordance—rising laboratory detections without commensurate increases in clinical presentations—suggests the season is in its earliest phase, with laboratory surveillance providing an early warning signal that has not yet translated into widespread symptomatic disease in the community.
The epidemiology of this early-onset season demonstrates clear patterns. All EU/EEA countries reporting data indicate dominance of influenza A viruses, with A(H3N2) largely driving the increasing trend in recent weeks. Specifically, in primary care (ILI/ARI) virological surveillance for week 46 of 2025, influenza accounted for 211 detections. Of these, 197 were influenza A (99% of typed influenza viruses), with 39 being A(H1)pdm09 (25% of influenza A), 119 being A(H3) (75% of influenza A), and 39 unsubtyped. Only two influenza B detections occurred. In hospital SARI surveillance for the same period, 115 influenza detections were reported, with 89 being influenza A (99% of typed viruses) and similar subtype distribution: 12 A(H1)pdm09 (52% of subtyped influenza A) and 11 A(H3) (48% of subtyped influenza A).
Genetic characterization of circulating influenza viruses provides critical insights into the antigenic composition of the circulating strains. Data from weeks 40-45 of 2025 show that among A(H1)pdm09 viruses characterized (141 viruses), 64% belonged to subclade 5a.2a.1(D.3.1), with 99% of these falling within the specific subclade 5a.2a.1(D.3.1) that corresponds to the vaccine strain. Among A(H3N2) viruses characterized (80 viruses), 36% belonged to subclade 2a.3a.1(K), with 82% within the dominant 2a.3a.1(K) subclade. Notably, this A(H3N2) subclade K has been the focus of ECDC’s heightened concern, as evidenced by the publication of a Threat Assessment Brief on 20 November 2025 specifically addressing the risk of influenza in the EU/EEA in the context of increasing circulation of A(H3N2) subclade K.
While the detailed content of this Threat Assessment Brief is not provided in the surveillance documents, the fact that ECDC devoted a specific assessment to this viral subclade indicates recognition of its potential significance—whether due to antigenic drift from vaccine strains, increased transmissibility, enhanced virulence, or other factors that could impact the severity of the coming influenza season. A(H3N2) viruses have historically been associated with more severe disease, particularly in elderly populations, and are notorious for their propensity to undergo antigenic drift, which can reduce vaccine effectiveness when circulating strains diverge significantly from vaccine composition.
The age distribution of influenza circulation shows expected patterns. Circulation is highest in children aged 5-14 years, who typically serve as important vectors for influenza transmission in communities due to their high contact rates in school settings and households. However, early increases in hospitalization are being observed in some countries affecting all age groups but primarily adults aged 65 years and above. This pattern raises concern, as elderly populations experience higher rates of severe outcomes from influenza including pneumonia, exacerbation of chronic conditions, hospitalization, and death.
The public health burden of influenza is substantial, with annual epidemics causing an estimated 3-5 million cases of severe illness globally and 290,000-650,000 respiratory deaths according to WHO estimates. In the EU/EEA, seasonal influenza causes significant morbidity, mortality, healthcare utilization, and economic impact through work absenteeism. The elderly, very young children, pregnant women, and individuals with chronic medical conditions bear disproportionate disease burden.
The unusually early start to the 2025-2026 season has several implications. First, it may result in a longer-than-usual influenza season, with correspondingly greater cumulative disease burden. Second, it creates temporal overlap with other respiratory viruses including RSV and SARS-CoV-2, potentially leading to co-circulation and even co-infections that could complicate clinical management and place additional strain on healthcare systems. Third, it provides less time for populations to receive seasonal influenza vaccination before virus circulation intensifies, potentially reducing the overall population-level impact of vaccination programs.
ECDC’s response to the early influenza activity includes the publication of the Threat Assessment Brief on A(H3N2) subclade K and urging those eligible for vaccination to get vaccinated without delay. This recommendation takes on particular urgency given the early onset of circulation and the fact that influenza vaccines require approximately two weeks post-administration to confer protection. For individuals planning to participate in mass gathering events such as the Jubilee celebrations in Italy (discussed in a separate section of the surveillance report), vaccination is especially important given the elevated transmission risk in crowded settings.
The mechanism of influenza transmission primarily involves respiratory droplets and aerosols produced through coughing, sneezing, or talking by infected individuals. Transmission can also occur through direct contact with contaminated surfaces (fomite transmission), though this route is considered less efficient than respiratory routes. The basic reproductive number (R0) for seasonal influenza typically ranges from 1-2, meaning each infected person transmits to one to two others on average in a fully susceptible population, though this can vary substantially based on viral characteristics, environmental conditions, and population behaviors.
From a clinical perspective, the cornerstone of influenza prevention remains annual vaccination. Current influenza vaccines are quadrivalent, containing antigens from two influenza A strains (A(H1N1)pdm09 and A(H3N2)) and two influenza B lineages (B/Victoria and B/Yamagata, though Yamagata has not been detected globally since 2020 and has been removed from some vaccine formulations). Vaccine effectiveness varies by season based on how well vaccine strains match circulating strains, with effectiveness typically ranging from 40-60% against medically attended illness in seasons with good match. Even when effectiveness is suboptimal, vaccination typically reduces disease severity and risk of complications.
Antiviral medications, particularly neuraminidase inhibitors (oseltamivir, zanamivir) and the polymerase inhibitor baloxavir marboxil, are available for treatment and prophylaxis. These medications are most effective when initiated early in illness (ideally within 48 hours of symptom onset) and are particularly recommended for individuals at high risk of complications, those with severe illness, and those requiring hospitalization.
Non-pharmaceutical interventions including respiratory etiquette, hand hygiene, staying home when ill, and in some circumstances use of masks in healthcare or high-risk settings complement pharmaceutical interventions. During influenza epidemics, healthcare facilities may implement additional measures including visitor restrictions, heightened infection control precautions, and active surveillance for healthcare-associated transmission.
The concurrent monitoring of other respiratory viruses provides important context. SARS-CoV-2 circulation is decreasing across all age groups in the EU/EEA, suggesting that COVID-19 is not currently contributing substantially to respiratory disease burden. The distribution of SARS-CoV-2 variants in weeks 43-44 of 2025 showed predominance of BA.2.86 (6% of detections), XFG (66%), and NB.1.8.1 (12%), indicating continued evolution of the virus though without apparent major phenotypic changes causing resurgence.
Respiratory syncytial virus circulation is low but showing slow increases approximately one week later than the previous season. RSV detections in week 46 included 32 viruses in primary care and 43 in hospitals. These increases are visible in both primary care and hospital surveillance data from several countries, with children under five years predominantly affected. RSV typically causes bronchiolitis in infants and young children, characterized by wheezing, respiratory distress, and in severe cases, requirement for hospitalization and respiratory support. In elderly adults and immunocompromised individuals, RSV can also cause serious lower respiratory tract disease.
The pattern of slowly increasing RSV circulation about one week behind last season’s timeline suggests that the 2025-2026 RSV season may follow a similar trajectory to the previous year, though week-to-week monitoring remains essential as seasonal patterns can shift. The temporal relationship between influenza and RSV circulation patterns—with influenza appearing earlier than usual while RSV follows close to its previous season’s timeline—may result in greater temporal overlap between these two important pediatric respiratory pathogens than occurred in some recent seasons.
Healthcare system implications of the early influenza season are already emerging. As noted, early increases in hospitalizations are being observed in some countries. As the season progresses and community circulation intensifies, hospitals can expect increased emergency department visits, hospital admissions, intensive care unit occupancy, and overall strain on healthcare resources. The impact on hospitalization remains limited at the current stage but bears close monitoring, particularly in regions experiencing more rapid increases in viral circulation.
Surveillance data quality and representativeness are generally high for influenza in the EU/EEA, with most countries participating in both sentinel primary care surveillance (for ILI/ARI) and hospital-based SARI surveillance. The integrated presentation of epidemiological and virological data through the ERVISS platform provides near-real-time situational awareness that enables rapid public health response. However, surveillance systems face ongoing challenges including varying case definitions across countries, changes in healthcare-seeking behavior, and the need to distinguish influenza from other causes of respiratory illness in the absence of laboratory confirmation.
Looking ahead, the remainder of the 2025-2026 influenza season will require sustained vigilance. Key areas for monitoring include the rate of increase in case numbers, the severity of disease as reflected in hospitalization and intensive care admission rates, the age distribution of severe cases, the effectiveness of current vaccine strains against circulating viruses (particularly A(H3N2) subclade K), the occurrence of antiviral resistance, and the cumulative burden of disease. Public health messaging should emphasize the importance of vaccination for eligible populations, early medical attention for individuals at high risk who develop influenza-like symptoms, and implementation of basic respiratory infection prevention measures to reduce transmission.
The early onset of the season serves as a reminder that influenza remains a formidable public health challenge despite availability of vaccines and antivirals. The unpredictability of seasonal timing, the propensity of influenza viruses (particularly A(H3N2)) to undergo antigenic drift, and the annual need to update vaccine composition based on surveillance of circulating strains make influenza a persistent threat requiring sustained investment in surveillance, research, and preparedness infrastructure.
Infectious Diseases: Bulgaria
Overview of Week 47 Surveillance Data
Bulgaria’s week 47 surveillance data encompass 41 notifiable infectious diseases, ranging from vaccine-preventable diseases to vector-borne infections, gastrointestinal pathogens, sexually transmitted infections, and bloodborne viruses. The data demonstrate the country’s comprehensive surveillance system while highlighting several notable trends and developments that warrant public health attention.
Respiratory and Droplet Transmission
Influenza and Influenza-like Illness
Bulgaria’s respiratory virus surveillance for week 47 does not show dramatic changes compared to the previous week, though the country is participating in the broader European trend of early influenza season onset. Specific Bulgarian influenza data are not detailed in the national surveillance report for week 47, but given Bulgaria’s inclusion in the EU/EEA surveillance network and the documented EU-wide trends, Bulgarian public health authorities should anticipate increasing influenza activity consistent with regional patterns.
The relatively stable respiratory disease picture in Bulgaria during week 47 contrasts with the more dynamic situation described in the EU/EEA surveillance summary, possibly reflecting lag in disease onset, differences in surveillance sensitivity or reporting, or genuine geographic heterogeneity in influenza circulation patterns. However, given the interconnectedness of European populations and the known rapid geographic spread of influenza, Bulgaria should prepare for potential intensification of influenza activity in coming weeks consistent with the regional pattern.
Pertussis (Whooping Cough)
During week 47 of 2025, Bulgaria registered one confirmed case of pertussis (whooping cough), representing no change from the previous week. From the beginning of 2025 through week 47, Bulgaria has registered 85 cases of pertussis. This marks a dramatic decrease compared to the same period in 2024, when 2,694 cases were registered—a decline of 2,609 cases or approximately 97%. This extraordinary reduction follows the substantial pertussis resurgence that occurred in 2024 across Europe and warrants careful examination.
Pertussis, caused by Bordetella pertussis, is a highly contagious respiratory disease that remains endemic globally despite widespread vaccination. The disease is characterized by paroxysmal coughing fits that can last for weeks or months, earning it the colloquial name “the 100-day cough.” Following an incubation period of 7-10 days, illness progresses through three stages: the catarrhal stage (1-2 weeks) resembling a common cold with runny nose, mild cough, and low-grade fever; the paroxysmal stage (2-6 weeks or longer) characterized by severe coughing fits often followed by a characteristic “whoop” sound during inspiration, post-tussive vomiting, and exhaustion; and the convalescent stage (weeks to months) with gradual recovery though cough may persist.
In infants, pertussis can be particularly severe, presenting with apneic episodes without the characteristic whoop, and carrying substantial risk of complications including pneumonia, seizures, encephalopathy, and death. The burden of disease and mortality are highest in infants too young to have completed the primary vaccination series.
The cyclical nature of pertussis epidemiology is well-recognized, with surges typically occurring every 3-5 years in most countries. The 2024 surge across Europe, including in Bulgaria, followed this expected pattern. The dramatic decline in 2025 likely reflects a combination of factors: depletion of the susceptible population during the 2024 surge (many individuals who would have been infected in 2025 were already infected in 2024), population immunity from recent vaccination and infection, and the expected downward phase of the epidemic cycle.
However, this decline should not lead to complacency. Pertussis remains endemic, and immunity from both vaccination and natural infection wanes over time, typically within 5-10 years. Sustained high vaccination coverage is essential to prevent future resurgences. Additionally, the single confirmed case in week 47 serves as a reminder that transmission continues at low levels even during inter-epidemic periods.
From a surveillance perspective, the 85 cases reported in 2025 through week 47 may underestimate true disease burden, as pertussis diagnosis requires high clinical suspicion and appropriate laboratory testing. Many cases, particularly in adolescents and adults who may have atypical presentations, likely go undiagnosed. PCR testing from nasopharyngeal specimens collected early in illness provides the most sensitive diagnostic approach, though serology can be useful for later presentations.
Scarlet Fever
Week 47 surveillance recorded 90 cases of scarlet fever in Bulgaria, representing a six-case increase from the previous week. These cases included 15 possible, 48 probable, and 27 confirmed cases. Year-to-date through week 47, Bulgaria has registered 3,150 cases of scarlet fever, compared to 7,925 cases during the same period in 2024—a decrease of 4,775 cases or 60%.
Scarlet fever, caused by Streptococcus pyogenes (group A Streptococcus) producing erythrogenic toxins, typically affects children aged 5-15 years. The disease is characterized by sore throat, fever, and a distinctive sandpaper-like rash that blanches with pressure, beginning on the neck and chest before spreading to other body areas. Additional features include strawberry tongue, circumoral pallor, and Pastia’s lines (linear petechiae in skin folds). The disease is spread through respiratory droplets and direct contact.
Treatment with appropriate antibiotics (typically penicillin or amoxicillin) shortens illness duration, reduces transmission, and prevents suppurative complications (peritonsillar abscess, cervical lymphadenitis) and non-suppurative sequelae including acute rheumatic fever and post-streptococcal glomerulonephritis. The dramatic decrease in cases compared to 2024 likely reflects natural fluctuation in streptococcal disease incidence, which can vary substantially year-to-year based on circulating strain types, population immunity, and environmental factors.
From a public health perspective, scarlet fever serves as a sentinel for group A streptococcal disease more broadly. Monitoring trends helps identify periods of increased streptococcal circulation that might also manifest as increases in more serious invasive group A streptococcal infections. The current moderate level of scarlet fever activity (90 cases in week 47) does not suggest unusual streptococcal circulation, though ongoing surveillance remains important.
Varicella (Chickenpox)
Bulgaria registered 442 cases of varicella during week 47, representing a 22-case increase from the previous week. Cases included 42 possible, 353 probable, and 47 confirmed. Year-to-date through week 47, 18,980 cases have been registered, compared to 23,818 cases during the same period in 2024—a decrease of 4,838 cases or 20%.
Varicella, caused by varicella-zoster virus (VZV), remains one of the most contagious infectious diseases, with secondary attack rates exceeding 90% in susceptible household contacts. Following an incubation period of 10-21 days (average 14-16 days), illness begins with prodromal symptoms of fever, malaise, and anorexia, followed within 24 hours by the characteristic rash. The rash typically begins on the face and trunk before spreading to extremities, progressing through macular, papular, vesicular, and crusted stages. New crops of lesions appear over several days, resulting in lesions at various stages of development simultaneously—a hallmark feature distinguishing varicella from other vesicular exanthems.
While typically a mild, self-limited disease in healthy children, varicella carries risk of complications including secondary bacterial infections of skin lesions (particularly with group A Streptococcus and Staphylococcus aureus), pneumonia, cerebellar ataxia, encephalitis, and in rare cases, necrotizing fasciitis or toxic shock syndrome. Adults, infants, pregnant women, and immunocompromised individuals face substantially higher risk of severe complications and mortality.
Bulgaria’s varicella vaccination policy and coverage rates influence disease epidemiology. The sustained moderate-to-high incidence (442 cases in week 47 despite being late November) indicates continued endemic circulation. The 20% decrease compared to 2024 may reflect several factors including natural year-to-year variation, increasing vaccination uptake if vaccination programs have expanded, and population immunity from previous exposure.
The seasonal pattern of varicella typically shows peaks in late winter and spring in temperate climates, with lower incidence during summer and early autumn. The observation of 442 cases in late November is consistent with the beginning of the usual high-transmission season. Healthcare providers should anticipate potential further increases in coming months and should counsel parents on recognition of complications warranting medical attention, particularly signs of bacterial superinfection (spreading erythema, increasing pain, fever recurrence after initial improvement) and neurological complications (severe headache, altered consciousness, ataxia).
Vector-Borne Transmission
Lyme Borreliosis
During week 47, Bulgaria registered five confirmed cases of Lyme borreliosis, unchanged from the previous week. Year-to-date through week 47, 373 cases have been registered, compared to 371 cases during the same period in 2024—representing a two-case increase or 0.5% change, essentially stable.
Lyme borreliosis, caused by spirochetes of the Borrelia burgdorferi sensu lato complex (primarily B. burgdorferi sensu stricto, B. garinii, and B. afzelii in Europe), is transmitted through bites of infected Ixodes ticks. Bulgaria’s geographic and ecological characteristics provide suitable habitat for tick populations, and Lyme borreliosis represents an important public health concern, particularly for individuals with occupational or recreational exposure to tick-infested environments including forestry workers, farmers, hunters, hikers, and campers.
The disease manifests in stages. Early localized infection (stage 1) typically presents with erythema migrans, an expanding annular rash that appears 3-30 days post-tick bite at the site of the bite. While often described as having a “bull’s-eye” appearance with central clearing, homogeneous erythema migrans without clearing is also common. Constitutional symptoms including fatigue, fever, headache, and arthralgias may accompany the rash.
Without treatment, infection can disseminate (early disseminated infection, stage 2), causing multiple erythema migrans lesions, facial nerve palsy or other cranial neuropathies, meningitis, carditis (particularly AV conduction abnormalities), and arthralgias. Late disseminated infection (stage 3) can develop months to years after initial infection and manifests as intermittent or chronic arthritis (particularly affecting large joints, especially the knee), chronic encephalomyelitis, or acrodermatitis chronica atrophicans (progressive skin changes predominantly on extensor surfaces of extremities).
Diagnosis in early disease relies primarily on recognition of erythema migrans in the appropriate epidemiological context (tick exposure in endemic area), as serology is often negative in early disease. For later manifestations, two-tier serological testing (screening ELISA or immunofluorescence assay followed by confirmatory Western blot) is standard. However, serology cannot distinguish active from past infection, and positive results in asymptomatic individuals are common in endemic areas, necessitating careful clinical correlation.
Treatment with appropriate antibiotics (doxycycline, amoxicillin, or cefuroxime for early disease; longer courses or intravenous ceftriaxone for neurological or cardiac involvement) is highly effective when initiated promptly. Prevention focuses on tick bite avoidance through protective clothing, use of repellents, environmental modifications to reduce tick habitat in residential areas, and prompt tick removal when bites occur (as transmission typically requires 36-48 hours of tick attachment).
The stable incidence of Lyme borreliosis in Bulgaria (373 cases year-to-date through week 47) during the current year suggests consistent surveillance and reporting. November represents the tail end of the tick activity season in Bulgaria, with peak transmission typically occurring in late spring and summer. The cases reported in week 47 likely represent a combination of late-season infections (as ticks can be active into late autumn during periods of mild weather) and delayed reporting of earlier infections.
Crimean-Congo Hemorrhagic Fever
Week 47 recorded one confirmed case of Crimean-Congo hemorrhagic fever (CCHF) in Bulgaria, unchanged from the previous week. Year-to-date through week 47, only this single case has been registered, compared to one case during the same period in 2024.
Crimean-Congo hemorrhagic fever, caused by CCHF virus (a nairovirus in the family Bunyaviridae), represents one of Bulgaria’s most serious endemic infectious diseases due to its high case fatality rate. The virus is maintained in nature through a tick-vertebrate-tick cycle, with Hyalomma ticks serving as both vectors and reservoirs. Multiple Hyalomma species can transmit the virus, and these ticks have a wide geographic distribution across Africa, Asia, Eastern Europe, and the Middle East.
Human infection occurs through tick bites, crushing infected ticks, contact with blood or tissues of infected livestock (particularly during slaughtering or veterinary procedures), or nosocomial transmission through contact with blood or body fluids of infected patients. Occupational groups at elevated risk include agricultural workers, veterinarians, slaughterhouse workers, and healthcare workers caring for CCHF patients.
Following an incubation period of 1-3 days after tick bite (or 5-6 days after contact with infected blood or tissues), illness begins abruptly with fever, myalgia, headache, and gastrointestinal symptoms. Within 3-5 days, hemorrhagic manifestations develop, including petechiae, ecchymoses, epistaxis, hematemesis, melena, and bleeding from mucous membranes and venipuncture sites. Hepatomegaly, tachycardia, and lymphadenopathy are common. Severe disease progresses to hepatic failure, pulmonary failure, disseminated intravascular coagulation, and shock. Case fatality rates range from 10-40% in various outbreak series, with death typically occurring during the second week of illness.
Diagnosis requires specialized laboratory testing including RT-PCR for viral RNA, ELISA for IgM and IgG antibodies, and viral isolation (requiring BSL-4 containment). Treatment is primarily supportive, focusing on fluid and electrolyte management, blood product replacement, and management of complications. Ribavirin has been used empirically in some patients, though evidence of efficacy is limited. Strict infection control measures are essential in healthcare settings to prevent nosocomial transmission, including isolation of patients, use of personal protective equipment, and safe handling of blood and body fluids.
Bulgaria has endemic CCHF transmission, with sporadic cases reported annually, primarily during the tick activity season (April-October). The single case reported in 2025 represents a relatively low incidence year, similar to 2024. However, even single cases warrant serious public health attention given the disease’s severity. Case investigation should include identification of the likely exposure source (tick bite vs. occupational exposure), contact tracing to identify individuals who may have had contact with patient blood or body fluids, and implementation of infection control measures in healthcare facilities that cared for the patient.
Prevention of CCHF requires multi-faceted approaches including personal protective measures to avoid tick bites (particularly for individuals working in or visiting tick-infested areas), use of appropriate personal protective equipment and safe work practices for those handling livestock or working in slaughterhouses, and rigorous infection control in healthcare settings. Public health education targeted to high-risk occupational groups is particularly important in endemic areas like Bulgaria.
Fecal-Oral Transmission
Salmonellosis
Bulgaria registered 16 confirmed cases of salmonellosis during week 47, representing a 12-case increase from the previous week. Year-to-date through week 47, 638 cases have been registered, compared to 882 cases during the same period in 2024—a decrease of 244 cases or 28%.
Salmonellosis, caused by non-typhoidal Salmonella species (particularly S. enteritidis and S. typhimurium), remains one of the most common bacterial foodborne infections globally. Transmission occurs primarily through consumption of contaminated food products, particularly undercooked poultry, eggs, unpasteurized dairy products, and produce contaminated through contact with animal feces or contaminated water. The infectious dose varies from fewer than 100 organisms for some virulent strains to over one million for less virulent strains, depending on bacterial strain virulence, food vehicle (high-fat foods may protect bacteria through the stomach’s acidic environment), and host factors.
Following an incubation period of 6-72 hours (typically 12-36 hours), illness begins with nausea, vomiting, abdominal cramps, and diarrhea (which may be bloody). Fever is common. In uncomplicated cases, illness is self-limited, resolving within 4-7 days. However, complications can occur, particularly in young children, elderly individuals, and immunocompromised persons. These complications include bacteremia (which can lead to focal infections such as osteomyelitis, endocarditis, or meningitis), severe dehydration requiring hospitalization, and post-infectious complications including reactive arthritis.
The 28% decrease in salmonellosis cases in 2025 compared to 2024 may reflect multiple factors including improved food safety practices, changes in food production and distribution, shifts in dietary patterns, or enhanced hygiene practices. However, the 12-case increase in week 47 compared to week 46 deserves attention to determine whether this represents a cluster or small outbreak requiring investigation.
Most salmonellosis cases do not require antibiotic treatment, as illness is self-limited and antibiotic use can prolong carriage and contribute to antimicrobial resistance. Treatment is supportive, focusing on hydration and electrolyte replacement. Antibiotics are reserved for patients with severe illness, those at high risk for invasive disease, and those with documented bacteremia or focal infections.
Prevention of salmonellosis requires multi-level interventions including farm-level biosecurity measures to reduce Salmonella colonization of food animals, food processing controls to minimize contamination, safe food handling and preparation practices (thorough cooking, avoiding cross-contamination, proper refrigeration), and in outbreak settings, identification and recall of contaminated products.
Gastroenteritis and Enterocolitis
Week 47 recorded 173 cases of gastroenteritis and enterocolitis in Bulgaria, representing a 26-case increase from the previous week. Cases included 68 possible, 94 probable, and 11 confirmed. Year-to-date through week 47, 8,679 cases have been registered, compared to 9,228 cases during the same period in 2024—a decrease of 549 cases or 6%.
This broad diagnostic category encompasses acute gastrointestinal infections of diverse etiologies including viral (norovirus, rotavirus, adenovirus, astrovirus), bacterial (in addition to those reported in specific categories like salmonellosis and campylobacteriosis), and parasitic pathogens. The category serves as a catch-all for clinically apparent gastroenteritis where specific etiology is not determined or where pathogens fall outside more specific surveillance categories.
The clinical presentation varies based on causative agent but typically includes some combination of diarrhea, vomiting, abdominal pain, fever, and malaise. Viral gastroenteritis, particularly norovirus, tends to have explosive onset with prominent vomiting, while bacterial gastroenteritis more often features fever and bloody diarrhea. Duration ranges from 24-48 hours for many viral etiologies to a week or more for some bacterial causes.
The public health significance of this surveillance category lies primarily in its utility for detecting outbreaks or unusual patterns of gastrointestinal disease that may not be captured through more specific diagnostic categories. The 6% decrease compared to 2024 and the relatively modest weekly case counts suggest stable endemic circulation without major outbreak activity. However, clusters of cases in specific settings (childcare facilities, schools, nursing homes, hospitals) warrant investigation even when overall population-level incidence is stable.
Prevention of gastroenteritis focuses on hand hygiene (particularly after toilet use and before food handling), safe food preparation practices, clean water supplies, appropriate exclusion of symptomatic individuals from food handling and childcare activities, and environmental cleaning and disinfection in settings where outbreaks occur. For viral gastroenteritis, bleach-based disinfectants are preferred over alcohol-based products, as norovirus and other enteric viruses are resistant to alcohol disinfection.
Escherichiosis (E. coli Infections)
Bulgaria registered six confirmed cases of escherichiosis during week 47, representing a two-case increase from the previous week. Year-to-date through week 47, 293 cases have been registered, compared to 339 cases during the same period in 2024—a decrease of 46 cases or 14%.
This category typically encompasses infections caused by diarrheagenic E. coli, including enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAEC), and Shiga toxin-producing E. coli (STEC, also known as verotoxigenic E. coli or VTEC). Each pathotype has distinct virulence mechanisms and clinical presentations.
STEC/VTEC, particularly serotype O157:H7 and other Shiga toxin-producing strains, warrants special attention due to its potential for severe complications including hemolytic uremic syndrome (HUS)—a triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure that occurs in approximately 5-10% of STEC infections, primarily affecting young children. HUS is the leading cause of acute renal failure in children in developed countries and can result in chronic renal impairment, hypertension, and other long-term sequelae.
STEC transmission occurs primarily through consumption of undercooked ground beef, unpasteurized dairy products, contaminated produce (particularly leafy greens), and contaminated water. Person-to-person transmission can occur, particularly in childcare settings. Cattle serve as the primary reservoir, with shedding in feces leading to environmental contamination.
Other pathotypes of diarrheagenic E. coli cause various clinical syndromes. ETEC is a common cause of travelers’ diarrhea, producing heat-labile and/or heat-stable enterotoxins that cause profuse watery diarrhea. EPEC causes persistent diarrhea particularly in young children in developing countries. EIEC causes dysentery-like illness with invasive disease of the colonic mucosa. EAEC is increasingly recognized as causing persistent diarrhea in both children and adults.
The diagnostic category of “escherichiosis” in Bulgarian surveillance presumably encompasses these various E. coli infections, though specific breakdown by pathotype would provide more actionable epidemiological information. The 14% decrease compared to 2024 suggests no major outbreak activity, though continued surveillance remains important to detect clusters that might indicate foodborne or waterborne outbreaks requiring public health intervention.
Treatment for most E. coli gastroenteritis is supportive. Notably, antibiotic treatment of STEC infections is contraindicated, as some studies suggest antibiotics may increase risk of HUS, possibly by inducing bacterial lysis and release of Shiga toxin. For other E. coli pathotypes, antibiotics may be considered in severe cases, though supportive care with hydration remains the mainstay of management.
Campylobacteriosis
Bulgaria registered 16 confirmed cases of campylobacteriosis during week 47, representing a two-case increase from the previous week. Year-to-date through week 47, 437 cases have been registered, compared to 307 cases during the same period in 2024—an increase of 130 cases or 42%.
Campylobacteriosis, caused primarily by Campylobacter jejuni and less commonly C. coli, is one of the most common bacterial causes of gastroenteritis globally. In many developed countries, campylobacteriosis has surpassed salmonellosis as the most frequently reported bacterial enteric infection. Transmission occurs primarily through consumption of undercooked poultry (the predominant source), unpasteurized milk, contaminated water, and contact with infected animals (particularly puppies and kittens with diarrhea).
Following an incubation period of 2-5 days, illness begins with prodromal symptoms of fever, headache, and myalgia, followed within 24 hours by abdominal pain (often severe and cramping) and diarrhea, which is frequently bloody. Illness typically resolves within a week without treatment, though symptoms can persist longer in some cases.
Complications, while uncommon, include bacteremia (particularly in immunocompromised individuals), post-infectious irritable bowel syndrome, reactive arthritis, and Guillain-Barré syndrome—an acute inflammatory demyelinating polyneuropathy that represents the most serious complication of campylobacteriosis. Approximately 30-40% of Guillain-Barré syndrome cases are preceded by Campylobacter infection, with cross-reactivity between antibodies to Campylobacter lipo-oligosaccharides and gangliosides on neural tissue hypothesized to mediate pathogenesis.
The 42% increase in campylobacteriosis cases in Bulgaria compared to 2024 is notable and contrasts with the decreased incidence observed for several other foodborne infections including salmonellosis. This pattern may reflect several factors including increased diagnostic testing and reporting, true increases in disease incidence related to changes in food production or consumption patterns, or differential outbreak activity.
Most campylobacteriosis cases do not require antibiotic treatment, as illness is self-limited. Antibiotics are considered for severe cases, immunocompromised individuals, and those with prolonged illness. Macrolides (particularly azithromycin) are generally preferred, though fluoroquinolones may be used in some settings, recognizing that fluoroquinolone resistance in Campylobacter is widespread in many regions due to fluoroquinolone use in poultry production.
Prevention focuses on safe food handling (particularly thorough cooking of poultry, preventing cross-contamination in kitchens), consumption of pasteurized dairy products, clean water supplies, and hand hygiene after contact with animals and before food preparation. At the regulatory level, interventions targeting reduction of Campylobacter colonization in poultry flocks and contamination of poultry carcasses during processing can reduce human disease burden.
Rotavirus Gastroenteritis
Week 47 recorded 13 confirmed cases of rotavirus gastroenteritis in Bulgaria, representing a six-case decrease from the previous week. Year-to-date through week 47, 681 cases have been registered, compared to 751 cases during the same period in 2024—a decrease of 70 cases or 9%.
Rotavirus is the leading cause of severe dehydrating diarrhea in children worldwide, particularly affecting infants and children under five years of age. Prior to vaccine introduction, rotavirus infected nearly every child by age five, causing substantial morbidity through dehydration, healthcare utilization, and parental work loss, and mortality particularly in developing countries with limited access to rehydration therapy.
Transmission occurs fecal-orally through direct person-to-person contact, contaminated surfaces and fomites, and possibly through respiratory droplets. The virus is extremely stable in the environment and highly infectious, with inocula as low as 10-100 viral particles capable of causing infection. Following an incubation period of 1-3 days, illness begins with vomiting, followed by profuse watery diarrhea lasting 3-8 days. Fever is common. Dehydration can develop rapidly, particularly in young infants.
Bulgaria’s rotavirus vaccination policy and coverage rates significantly influence disease epidemiology. Where high vaccination coverage is achieved with either RotaTeq or Rotarix vaccines (the two WHO-prequalified rotavirus vaccines), dramatic reductions in rotavirus hospitalizations and emergency department visits have been documented, with herd immunity effects protecting even unvaccinated individuals through reduced community transmission.
The 9% decrease in cases compared to 2024 may reflect increasing vaccination coverage if Bulgaria has recently enhanced its rotavirus immunization programs, though other factors including natural year-to-year variation and possibly impacts of COVID-19 pandemic-related behavioral changes on transmission of enteric pathogens may also contribute.
Treatment is supportive, focusing on rehydration (oral rehydration solution preferred; intravenous fluids for severe dehydration). Zinc supplementation may modestly reduce diarrhea duration and severity. Prevention relies primarily on vaccination, with rotavirus vaccines recommended by WHO for inclusion in all national immunization programs. Additional preventive measures include hand hygiene, though rotavirus’s environmental stability and high infectivity limit the effectiveness of hygiene measures alone in preventing transmission.
Contact and Direct Transmission
HIV Infection
Bulgaria registered two confirmed cases of HIV infection during week 47, representing a three-case decrease from the previous week. Year-to-date through week 47, 274 cases have been registered, compared to 254 cases during the same period in 2024—an increase of 20 cases or 8%.
This modest increase in HIV diagnoses compared to the previous year warrants attention as part of ongoing HIV surveillance and prevention efforts. HIV epidemiology varies substantially across European countries, with different predominant transmission routes (men who have sex with men, injecting drug use, heterosexual transmission) and epidemic characteristics.
Several factors may contribute to changes in reported HIV case counts, including true changes in incidence (new infections), changes in testing rates or testing strategies, migration patterns affecting the population at risk, and changes in reporting practices. The categorization as new HIV diagnoses in surveillance systems typically includes both recent and long-standing infections that are newly diagnosed, distinguishing them from incident infections (true new acquisitions of infection).
From a public health perspective, the number of new HIV diagnoses reflects both HIV incidence and testing coverage. Increases in diagnosis numbers may represent either increasing incidence (concerning) or increasing testing uptake (potentially positive, as it brings more people into care). Detailed epidemiological analysis examining transmission categories, CD4 counts at diagnosis (as surrogate for timing of infection and late diagnosis), viral sequences (to identify transmission clusters), and testing patterns is essential to interpret trends appropriately.
Sexually Transmitted Infections - Syphilis, Congenital Syphilis, Gonorrhea, Chlamydia
Bulgaria’s surveillance data for sexually transmitted infections (STIs) show mixed patterns. Syphilis cases numbered nine in week 47 (representing a five-case decrease from week 46), with 332 cases year-to-date compared to 299 in 2024 (an 11% increase). Congenital syphilis recorded no cases in week 47 (down one from week 46), with 34 cases year-to-date compared to 13 in 2024 (a 161% increase). Gonorrhea cases numbered two in week 47 (unchanged from week 46), with 109 cases year-to-date compared to 84 in 2024 (a 30% increase). Urogenital chlamydia infection recorded one case in week 47 (down one from week 46), with 170 cases year-to-date compared to 98 in 2024 (a 73% increase).
The pattern across these STIs shows concerning increases compared to 2024, with particularly dramatic rises in congenital syphilis (161%), chlamydia (73%), and substantial increases in gonorrhea (30%) and syphilis (11%). These increases align with broader European and global trends of rising STI incidence following decades of declining rates, likely driven by multiple factors including changes in sexual behavior, reduced fear of HIV/AIDS with effective treatment availability, decreased condom use, substance use facilitating risk behaviors, and possibly increased testing and reporting.
The 161% increase in congenital syphilis cases is particularly alarming, as congenital syphilis is entirely preventable through routine prenatal screening and treatment of syphilis-infected pregnant women. Congenital syphilis can result in stillbirth, neonatal death, and serious sequelae in surviving infants including skeletal abnormalities, neurological impairment, and multiorgan disease. Every case of congenital syphilis represents a failure of the healthcare system to screen and treat the mother during pregnancy.
This dramatic increase in congenital syphilis suggests gaps in Bulgaria’s prenatal care system that require urgent attention. Potential contributing factors include inadequate prenatal care attendance, failure to screen pregnant women for syphilis, delayed diagnosis or treatment initiation, treatment failure due to inappropriate regimens or adherence problems, or reinfection of treated women before delivery. Public health response should include review of prenatal screening protocols, ensuring all pregnant women receive screening early in pregnancy (with repeat screening in third trimester for high-risk women), prompt treatment with benzathine penicillin G for diagnosed cases, partner notification and treatment, and addressing barriers to prenatal care access.
The increases in other STIs reflect the urgent need for comprehensive sexual health services including accessible STI testing, prompt treatment, partner notification and treatment, sexual health education, and promotion of condom use and other preventive measures. The rise in gonorrhea is particularly concerning given increasing antimicrobial resistance in Neisseria gonorrhoeae, with resistance to fluoroquinolones widespread, resistance to azithromycin increasing, and emerging resistance to extended-spectrum cephalosporins (the last remaining first-line treatment options) documented in some regions.
For chlamydia, the 73% increase may partly reflect expanded testing, as chlamydia is often asymptomatic and many cases historically went undiagnosed. However, true increases in incidence likely also contribute. Untreated chlamydia can lead to serious reproductive health consequences including pelvic inflammatory disease, ectopic pregnancy, and infertility in women, and epididymitis and reactive arthritis in men.
From a public health perspective, STI control requires multi-component strategies including promotion of safer sexual practices, accessible testing services (including expansion of self-testing where appropriate), prompt treatment using antimicrobial stewardship principles to preserve effectiveness of existing treatments, partner notification and treatment, targeted interventions for populations at disproportionate risk, and continued surveillance including antimicrobial resistance monitoring.