Executive Summary
Week 6 of 2026 is dominated by a critical multi-country food safety crisis involving cereulide toxin contamination of infant formula products that poses moderate risk to infants across the EU/EEA and globally. Belgium has confirmed five cases through laboratory testing of faecal samples, while France, Spain, Denmark, and the United Kingdom are investigating additional suspected cases following consumption of recalled products. The root cause has been identified as contaminated arachidonic acid oil used as an ingredient across multiple manufacturers and product lines. Respiratory virus circulation remains elevated throughout Europe, with influenza activity widespread and respiratory syncytial virus continuing to increase primarily among children under five years of age. In Bulgaria, gastroenteritis cases increased 29.4% week-over-week, while year-to-date acute viral hepatitis surveillance shows cases 146% higher than the corresponding period in 2025, maintaining a concerning trend observed throughout early 2026. India reported two confirmed Nipah virus disease cases among healthcare workers in West Bengal, triggering enhanced surveillance and contact tracing for 196 individuals. Emerging vector control research from Singapore demonstrated highly effective dengue suppression using sterile Wolbachia-infected male mosquitoes.
Non-Communicable Disease and Healthcare System Developments
Breakthrough Gene Therapy for Fatal Neurodegenerative Disease
Phase 1-2 trial results published in the New England Journal of Medicine demonstrate preliminary efficacy of AAV9-delivered gene therapy for type II GM1 gangliosidosis, a fatal lysosomal storage disorder caused by β-galactosidase deficiency. GM1 gangliosidosis results from biallelic pathogenic variants in the GLB1 gene and leads to progressive neurodegeneration with accumulation of GM1 ganglioside in lysosomes. The disease manifests in three clinical forms based on age of onset, with type II presenting in late infancy or early childhood and characterized by progressive motor and cognitive decline, typically proving fatal within the first decade of life.
The trial enrolled nine children with type II GM1 gangliosidosis who received a single intravenous infusion of adeno-associated virus serotype 9 encoding human β-galactosidase along with immunosuppression. Over a three-year observation period, all participants demonstrated increased cerebrospinal fluid β-galactosidase activity and decreased GM1 ganglioside concentrations, suggesting biological target engagement. Neuroimaging revealed patterns consistent with reduced cerebral atrophy rates and favorable myelination changes compared to baseline. Clinical assessments showed stabilization of expressive communication and gross motor function, though fine motor and receptive communication scores declined. The median Clinical Global Impression-Improvement score was 3 (minimal improvement) at two years and 4 (no change) at three years, comparing favorably to historical controls who show progressive deterioration.
Safety concerns emerged during the trial, with 124 adverse events recorded over three years, 30 of which were deemed possibly, probably, or definitely related to gene therapy. All nine participants experienced elevated serum aspartate and alanine aminotransferase levels that returned to baseline by 18 months. One participant required hospitalization for severe vomiting attributed to the therapy. The findings suggest that AAV9-mediated gene delivery can achieve biochemical correction and may slow disease progression in some domains, though significant adverse events and incomplete clinical benefit indicate the need for further optimization. This represents the first demonstration of potential therapeutic benefit in this universally fatal condition and establishes proof-of-concept for gene therapy approaches to lysosomal storage disorders affecting the central nervous system.
Novel Dengue Vector Control Technology Demonstrates High Efficacy
A cluster-randomized trial conducted in Singapore has validated a novel approach to dengue control using repeated release of male Aedes aegypti mosquitoes infected with the wAlbB strain of Wolbachia pipientis bacteria. The intervention exploits cytoplasmic incompatibility whereby wild-type female mosquitoes that mate with Wolbachia-infected males produce nonviable offspring, potentially suppressing mosquito populations and reducing dengue virus transmission. Dengue represents a major public health threat across tropical and subtropical regions, with Aedes aegypti serving as the primary vector. Singapore, despite intensive traditional vector control efforts, experiences recurrent dengue outbreaks with substantial morbidity.
The trial divided 15 geographic population clusters into intervention clusters (393,236 residents) receiving deployments of Wolbachia-infected males and control clusters (331,192 residents) receiving no deployments. Adult wild-type Aedes aegypti populations were suppressed across intervention clusters, with average mosquito abundance decreasing from 0.18 at baseline to 0.041 from three months post-intervention through the 24-month trial period, compared to 0.277 in control clusters. In the intention-to-treat analysis examining outcomes at six months or more post-intervention, 6% of residents in intervention clusters tested positive for dengue (354 of 5,722 tests) compared to 21% in control clusters (1,519 of 7,080 tests). The protective efficacy of the intervention, calculated as (1 − odds ratio) × 100, ranged from 71% to 72% with three to twelve months or more of Wolbachia mosquito exposure, represented by odds ratios of 0.28 to 0.29.
This trial provides rigorous evidence that sterile insect technique using Wolbachia-infected males can achieve substantial suppression of Aedes aegypti populations and dramatic reductions in dengue infection risk in a real-world urban setting. The approach represents a fundamentally different paradigm from traditional vector control methods such as insecticide application or source reduction, offering potential advantages including species specificity, absence of chemical residues, and reduced likelihood of insecticide resistance development. The sustained effectiveness observed over 24 months suggests the method can provide durable protection when releases are maintained. These findings have significant implications for dengue control strategies globally, particularly in urban tropical settings where traditional methods have proven insufficient to prevent epidemic transmission.
Infectious Diseases: Global Perspective
Respiratory and Droplet Transmission
Nipah Virus Disease Outbreak Among Healthcare Workers in India
India reported two laboratory-confirmed cases of Nipah virus disease among healthcare workers in North 24 Parganas district, West Bengal State, representing the country’s first Nipah cases since 2025 when four cases (two fatal) were reported from Kerala. The confirmed cases are nurses aged 20-30 years, one male and one female, working at the same private hospital in Barasat. Both developed symptoms typical of severe Nipah infection in late December 2025 and were admitted to hospital in early January 2026. Diagnosis was confirmed at the National Institute for Virology in Pune on 13 January 2026 using real-time polymerase chain reaction and enzyme-linked immunosorbent assay testing. As of 21 January 2026, one patient showed clinical improvement while the other remained under critical care. Media reports suggest five total cases in the outbreak, though only two have been officially confirmed.
Nipah virus (Henipavirus nipahense) belongs to the family Paramyxoviridae and was first identified during a 1999 outbreak in Malaysia and Singapore. The virus maintains a natural reservoir in Pteropus fruit bats and can transmit to humans through direct contact with infected animals, consumption of food contaminated by bat excreta (particularly raw date palm sap), or person-to-person transmission through close contact with infected individuals or contaminated materials. The incubation period typically ranges from four to 14 days, with clinical manifestations varying from mild symptoms including fever, headache, muscle pain, and nausea to severe presentations with acute respiratory distress syndrome and encephalitis. Case fatality rates in previous outbreaks have ranged from 40% to 75%, with survivors sometimes experiencing persistent neurological sequelae. West Bengal previously experienced Nipah outbreaks in 2001 (Siliguri) and 2007 (Nadia district).
Public health authorities in India implemented comprehensive response measures including enhanced surveillance, laboratory testing capacity expansion, field investigations, and contact tracing. A total of 196 contacts were identified and tested negative for Nipah virus as of 27 January 2026, with no additional cases reported to date according to the Indian Ministry of Health and Family Welfare. Investigation into the source of exposure is ongoing, with media reporting that both nurses had attended to a patient with Nipah-like symptoms at their hospital, though this has not been confirmed through official sources. One nurse reportedly traveled to a village in Nadia district near the Bangladesh border and may have consumed raw date palm sap, a known transmission route when contaminated by bat saliva. Neighboring countries including Thailand, Nepal, and Cambodia initiated precautionary measures including information campaigns and screening for passengers arriving from India at airports, reflecting regional concern about potential cross-border transmission.
The likelihood of exposure to and infection with Nipah virus for EU/EEA citizens traveling to or residing in India remains very low given the limited number of infections and geographic containment of cases to date. However, the occurrence of healthcare-associated transmission demonstrates the continued risk Nipah poses as a high-consequence pathogen with pandemic potential. The virus’s high case fatality rate, capacity for person-to-person transmission in healthcare settings, absence of specific antiviral therapies or licensed vaccines, and wide geographic distribution of natural bat reservoirs across South and Southeast Asia necessitate sustained vigilance. Healthcare systems must maintain preparedness for potential imported cases, with emphasis on early recognition, appropriate infection prevention and control measures including respiratory precautions, and prompt notification to public health authorities.
Fecal-Oral Transmission
Critical Multi-Country Food-Borne Incident: Cereulide Toxin in Infant Formula
A multi-country food safety crisis emerged following detection of cereulide, the emetic toxin produced by Bacillus cereus, in infant nutrition products manufactured by multiple companies and distributed globally. The contamination was traced to arachidonic acid oil, an omega-6 fatty acid supplement routinely added to infant formula, which became contaminated during production. Cereulide is a cyclic dodecadepsipeptide toxin notable for extreme heat stability, acid resistance, and protease resistance, enabling it to survive standard food processing conditions including pasteurization and sterilization. Following ingestion, the toxin acts on mitochondria causing cellular dysfunction and manifests clinically with rapid-onset nausea and vomiting, typically within one to five hours post-consumption.
The precautionary recall was initiated in December 2025 and expanded in January 2026 as the scope of contamination became apparent, affecting numerous batches, products, and brands distributed across EU/EEA Member States and countries worldwide. Multiple European food safety authorities issued recalls reported under RASFF notifications 2025.9962, 2026.0027, 2026.0173, 2026.0179, 2026.0196, 2026.0509, 2026.0347, 2026.0407, 2026.0663, 2026.0542, 2026.0598, 2026.0177, and 2026.0647. Belgium reported five infants with cereulide-positive faecal samples, representing the only laboratory-confirmed cases to date as cereulide toxin analysis in biological specimens is not routinely available in clinical microbiology laboratories. All five Belgian cases had consumed recalled infant formula and experienced favorable clinical outcomes. Of the infant formula products consumed by these cases, three of five samples tested positive for cereulide; the remaining two samples may not undergo testing.
France reported 11 hospitalized infants investigated by Regional Health Agencies, all of whom recovered and returned home. Of these 11 cases, five consumed recalled infant formula while six could not be confirmed as having consumed implicated products. Notably, winter-related gastroenteritis is currently active in France, and five of the 11 hospitalized children received differential diagnoses explaining their gastrointestinal symptoms. Two unexplained infant deaths were notified in France and are under medicolegal investigation per routine protocols; approximately 300 unexplained infant deaths occur annually in France. Both deceased infants had consumed recalled infant formula, though no causal link has been established between formula consumption and these deaths. Spain reported eight cases with vomiting, five requiring hospitalization, all with history of consumption of potentially affected products, though none were laboratory-confirmed. Denmark’s food safety authority received reports of infants developing diarrhea following consumption of recalled products, but no confirmed or probable cases have been identified as samples were not investigated for toxin presence. The United Kingdom reported 36 cases with gastrointestinal symptoms following consumption of implicated batches distributed across England (24 cases), Scotland (7), Wales (3), Northern Ireland (1), and Crown Dependencies (1), with testing of recalled formula confirming cereulide presence.
The recalled products’ wide distribution creates moderate to high likelihood of exposure for infants consuming formula in affected regions. Impact of exposure and symptom development is low to moderate depending on infant age, with neonates and young infants less than six months potentially more vulnerable to dehydration and electrolyte disturbances. The overall risk to children under one year in the EU/EEA is assessed as moderate for this incident. However, as contaminated products have been identified and recalled, current exposure likelihood is decreasing, correspondingly reducing overall risk. The European Food Safety Authority, upon request from the European Commission, established an acute reference dose for cereulide in infants and estimated cereulide concentrations in infant formula of potential safety concern on 2 February 2026, providing guidance to risk managers for determining when products should be withdrawn as precautionary public health measures.
ECDC and EFSA are jointly developing a Rapid Outbreak Assessment to support Member States in managing this incident, with publication planned for 19 February 2026. Member States are encouraged to share case information and investigation details through the EpiPulse event system and to collaborate closely with national food safety authorities when suspected cases are identified to investigate potential links to recalled formula batches. Consumers are advised to follow instructions from national food safety authorities, and parents, guardians, and caregivers possessing affected products should not feed them to infants and young children. This incident highlights vulnerabilities in global infant nutrition supply chains and the challenges of detecting and responding to contamination with unusual toxins not routinely screened in food safety testing programs.
Contact and Sexual Transmission
Chikungunya Case Without Travel History in Bulgaria
Bulgaria reported one confirmed case of chikungunya during Week 6, representing an increase of one case compared to the previous week and bringing the year-to-date total to three cases compared to zero during the same period in 2025. The case was laboratory confirmed though clinical and epidemiological details were not provided in surveillance reports. Chikungunya virus is an alphavirus transmitted primarily by Aedes aegypti and Aedes albopictus mosquitoes, causing acute febrile illness characterized by high fever and severe, often debilitating polyarthralgia. Joint pain may persist for weeks to months, occasionally progressing to chronic arthritis. The virus is endemic in tropical and subtropical regions of Africa, Asia, and the Americas, with Aedes albopictus established in multiple European countries including Bulgaria, creating theoretical potential for autochthonous transmission during warmer months.
The occurrence of a chikungunya case in February, outside the typical mosquito activity season in Bulgaria, strongly suggests travel-associated acquisition rather than local transmission. The absence of epidemiological details in the surveillance report precludes definitive determination of exposure source. However, the detection underscores the importance of considering arboviral infections in travelers returning from endemic regions presenting with acute febrile illness and arthralgia, even during winter months. Healthcare providers should maintain awareness of travel-associated arboviral diseases and ensure appropriate diagnostic testing. The presence of competent vectors in Bulgaria and other European countries necessitates continued surveillance for potential autochthonous transmission during mosquito activity seasons, though the risk remains low under current climatic and vectorial conditions.
Infectious Diseases: European Union/European Economic Area
Respiratory and Droplet Transmission
Respiratory Virus Epidemiology: Influenza Season Progression and RSV Surge
Respiratory virus circulation across the EU/EEA remains elevated during Week 6, with the number of people experiencing respiratory illness symptoms continuing to increase since the start of 2026, indicating widespread transmission. The 2025-26 influenza season, which began unusually early in November 2025, shows heterogeneous progression across the region, with some countries reporting peaked activity while others appear to be approaching their epidemic peaks. This seasonal timing represents the earliest sustained influenza activity observed in recent years.
Influenza virus detection rates remain high across sentinel surveillance networks, with influenza A continuing to dominate. Both A(H1N1)pdm09 and A(H3N2) viruses are co-circulating, though relative proportions vary by country and week. Influenza B detections remain sporadic and at low levels. Age-stratified surveillance data indicate that children aged 5-14 years represent the primary demographic group driving community transmission, with increases observed both in mild illness presentations in primary care settings and more severe disease requiring hospitalization. Despite overall hospitalization rates decreasing compared to early January 2026, adults aged 65 years and over continue to account for the majority of hospital admissions, intensive care unit admissions, and deaths attributable to influenza. This age-stratified disease burden pattern is consistent with historical influenza epidemiology, wherein infection rates are highest among school-age children while severe outcomes concentrate among elderly adults and individuals with underlying medical conditions.
Early estimates of seasonal influenza vaccine effectiveness for the 2025-26 season published by ECDC on 19 December 2025 show concordance with estimates for A(H3N2) viruses published by other countries, suggesting the vaccine formulation provides moderate protection against circulating strains. However, vaccine uptake remains suboptimal in many EU/EEA countries, particularly among high-risk populations who would benefit most from protection against severe outcomes. Given the early season onset and current high circulation levels, ECDC continues to urge eligible individuals to receive influenza vaccination without delay, as substantial seasonal activity persists and vaccination remains beneficial even after season onset.
Respiratory syncytial virus circulation is elevated and continues to increase across the EU/EEA, representing a continuation of trends observed in recent weeks. The current RSV season began later than the previous two seasons, with activity typically peaking in late autumn or early winter. Children under five years of age are disproportionately affected by RSV infection and account for most hospitalizations. RSV characteristically causes bronchiolitis in infants, presenting with cough, wheezing, tachypnea, and respiratory distress. Young infants, particularly those under six months, premature infants, and children with underlying cardiac or pulmonary conditions face highest risk for severe disease requiring hospitalization and supplemental oxygen. The concurrent elevation of both influenza and RSV activity places strain on pediatric healthcare services, with some countries reporting capacity challenges in pediatric wards and pediatric intensive care units.
SARS-CoV-2 circulation remains low across all age groups throughout the EU/EEA. The number of hospitalisations attributable to COVID-19 is currently limited compared to influenza and RSV. Variant surveillance based on limited sequencing data from five EU/EEA countries for weeks 2-3 of 2026 shows XFG remains the dominant variant at 47.6% median proportion, with NB.1.8.1 at 23.1% and newly designated variant under monitoring BA.3.2 at 6.7%. The variant of interest BA.2.86 represents 0.0% of sequenced samples. Low overall SARS-CoV-2 transmission, reduced reporting, and limited testing volumes constrain accurate assessment of variant dynamics.
EuroMOMO reports substantially elevated levels of all-cause mortality during Week 6, primarily driven by increased mortality in several countries in age groups above 65 years. This elevation is consistent with the combined burden of circulating respiratory viruses, particularly influenza, and seasonal factors affecting elderly populations during winter months. The mortality signal underscores the public health importance of interventions to protect vulnerable populations during periods of high respiratory virus transmission.
Fecal-Oral Transmission
Norovirus Outbreak at Winter Olympic Games
The organizing committee for the Milano Cortina 2026 Winter Olympic Games reported a norovirus outbreak among the Finnish female ice hockey team at the Olympic Village on 4 February 2026. Norovirus is the most common cause of acute gastroenteritis worldwide and notorious for causing outbreaks in closed or semi-closed settings including cruise ships, hotels, hospitals, schools, and sporting event venues. The virus is extremely contagious, with very low infectious dose (10-100 viral particles), multiple transmission routes including person-to-person contact, contaminated food and water, and environmental surfaces, and environmental stability allowing prolonged survival on surfaces. Clinical illness typically begins 12-48 hours post-exposure with sudden onset of nausea, projectile vomiting, watery diarrhea, and abdominal cramps, generally self-limiting within 24-72 hours though dehydration may occur, particularly in young children and elderly adults.
The source of infection remains under investigation. Finnish health authorities confirmed that disease control measures are in place including isolation of cases, quarantine of close contacts, and physical distancing protocols. These interventions align with established norovirus outbreak management principles emphasizing rapid case identification and isolation, thorough environmental disinfection with appropriate agents (quaternary ammonium compounds are ineffective; chlorine-based disinfectants or other EPA-registered products with demonstrated norovirus efficacy are required), exclusion of ill individuals from food handling and competition for at least 48 hours after symptom resolution, and emphasis on hand hygiene, though alcohol-based hand sanitizers have limited efficacy against norovirus and handwashing with soap and water is preferable.
ECDC initiated monitoring of communicable disease events associated with the Winter Olympic Games on 2 February 2026 and continues surveillance through close collaboration with Italian National Institute of Health (Istituto Superiore di Sanità). The Games, taking place from 4-22 February 2026 with venues spanning Northern Italy including Milan, Cortina d’Ampezzo, Valtellina, Val di Fiemme, and Anterselva, are expected to attract more than one million cumulative attendees. Mass gathering events create elevated risk for communicable disease transmission due to crowding, international travel bringing together populations with varying immunity profiles and pathogen exposures, shared facilities, and potential strain on local public health and healthcare systems. The probability of EU/EEA citizens acquiring communicable diseases during the Winter Olympics remains low if general preventive measures are applied, including vaccination according to national schedules, hand and respiratory hygiene, appropriate food handling, self-isolation when symptomatic, and seeking prompt medical attention if needed.
Mpox: Evolution of Clade I Transmission Patterns
The global mpox epidemiological situation continues to evolve, with both clade I and clade II circulating. On the African continent, the five countries reporting most confirmed and suspected clade I cases in 2025 were Democratic Republic of the Congo, Uganda, Burundi, Kenya, and Zambia. According to WHO, during the past six weeks ending 1 February 2026, most confirmed clade I cases were reported by DRC and Madagascar (253 and 196 cases, respectively). Madagascar reported confirmed mpox clade Ib cases for the first time in December 2025, with confirmed cases subsequently reported from eight regions and suspected cases from 20 of 24 regions. Comoros reported four clade Ib cases imported from Madagascar in January 2026. Overall, a decreasing trend in clade I mpox cases has been reported from Africa since May 2025, though week-to-week fluctuations occur.
In the EU/EEA, travel-associated or locally-acquired clade I cases have been reported by Sweden (2024), Germany (2024-2025), Belgium (2024-2025), France, Ireland, Italy, and Spain (2025), Greece (October 2025), Romania (December 2025), and Czechia (January 2026). Since October 2025, a new transmission pattern has emerged with Italy, the Netherlands, Portugal, and Spain reporting mpox clade I in men without travel history. In the Netherlands and Spain, these were men reporting sexual contact with other males. The United States reported three clade I cases in California without travel history, with phylogenetic analysis indicating the sequences cluster with a previously reported travel-associated case, and epidemiological investigation indicating possible ongoing transmission among gay, bisexual, and other men who have sex with men and their social networks.
Confirmed limited secondary transmission of clade I within households has been reported in the EU/EEA primarily among household contacts since 2024 by Germany, Belgium, and Ireland. Outside the EU/EEA and Africa, secondary transmission has been reported in the United Kingdom, China, Qatar, and Australia, with the number of secondary cases remaining low (range 1-6 cases per event). Based on available information, all transmission events resulted from close contact with no deaths reported. ECDC updated its classification of transmission patterns on 3 February 2026, categorizing countries as having either “community transmission” or “travel-associated cases or limited transmission” based on epidemiological data adequacy and observed transmission patterns. Countries with community transmission include Burundi, Central African Republic, Congo, DRC, Ethiopia, Kenya, Madagascar, Malawi, Mozambique, Rwanda, Tanzania, Uganda, United Arab Emirates, and Zambia.
ECDC’s assessment considers the risk of clade Ib infection moderate for men who have sex with men and low for the general population in the EU/EEA, reflecting current evidence and considerable uncertainties around transmissibility and severity of clade Ib infection relative to clade IIb. The detection of autochthonous transmission among men who have sex with men indicates the virus is following transmission patterns similar to clade IIb, which has circulated at low levels in sexual networks in countries worldwide since 2022. Primary preventive vaccination strategies should prioritize gay, bisexual, and transgender people and men who have sex with men at higher risk of exposure based on epidemiological or behavioral criteria, alongside individuals at risk of occupational exposure. Post-exposure preventive vaccination should target close contacts of cases. Healthcare providers should maintain awareness of mpox as a possible diagnosis in patients presenting with characteristic rash, particularly those with epidemiological risk factors.
Infectious Diseases: Bulgaria
Fecal-Oral Transmission
Gastroenteritis Surge Continues Post-Holiday Period
Bulgaria reported 143 cases of gastroenteritis and enterocolitis during Week 6, representing a 42-case increase (29.4% week-over-week growth) compared to the 101 cases reported in Week 5. Of the 143 cases, 57 were classified as possible, 77 as probable, and 9 as confirmed through laboratory testing. This substantial increase extends the post-holiday acceleration in gastrointestinal disease activity observed since early January 2026. Year-to-date through Week 6, Bulgaria has registered 793 gastroenteritis cases compared to 778 during the same period in 2025, representing a modest 1.9% increase that does not fully capture the sharp week-over-week acceleration observed in recent weeks.
Acute gastroenteritis encompasses a spectrum of etiologies including viral pathogens (norovirus, rotavirus, adenovirus, sapovirus, astrovirus), bacterial agents (Salmonella, Campylobacter, Shigella, pathogenic Escherichia coli, Yersinia), and parasitic organisms (Giardia, Cryptosporidium). In temperate climates during winter months, viral etiologies predominate, with norovirus responsible for the majority of epidemic gastroenteritis in all age groups. Norovirus exhibits peak activity during cooler months, thrives in closed or semi-closed settings, demonstrates extreme contagiousness with infectious doses as low as 10-100 viral particles, and spreads through person-to-person contact, contaminated food and water, and environmental surfaces. Clinical presentation typically includes sudden onset of nausea, vomiting, watery diarrhea, and abdominal cramps, with illness generally self-limiting within 24-72 hours, though dehydration may necessitate medical attention, particularly among young children, elderly adults, and immunocompromised individuals.
The 29.4% week-over-week increase likely reflects multiple contributing factors. Post-holiday transmission following increased social mixing during New Year celebrations and Orthodox Christmas (celebrated 7 January in Bulgaria) creates conditions for respiratory and enteric pathogen transmission. Return to school and workplace settings after holiday breaks facilitates introduction of pathogens into households and communities. Winter conditions favor persistence of enteric viruses in the environment and on surfaces. Additionally, reporting patterns may reflect healthcare-seeking behavior changes as routine medical services resume full capacity following holiday periods.
Public health authorities should emphasize prevention measures during periods of elevated gastroenteritis transmission. Hand hygiene with soap and water (alcohol-based sanitizers have limited efficacy against norovirus) represents the single most important preventive measure. Proper food handling and preparation, thorough cleaning and disinfection of environmental surfaces using chlorine-based or other appropriate disinfectants, exclusion of symptomatic individuals from food handling and childcare/healthcare settings for at least 48 hours after symptom resolution, and prompt medical attention for individuals developing signs of dehydration (decreased urine output, lethargy, dry mucous membranes) are critical. Healthcare facilities should maintain vigilance for potential norovirus outbreaks and implement appropriate infection prevention and control measures including contact precautions for affected patients.
Respiratory and Droplet Transmission
Varicella Remains Elevated; Scarlet Fever Activity Continues
Varicella cases totaled 563 during Week 6, representing a minimal increase of 5 cases (0.9%) compared to Week 5. Of the 563 cases, 75 were classified as possible, 440 as probable, and 48 as confirmed. Year-to-date through Week 6, Bulgaria has registered 3,448 varicella cases compared to 3,970 during the same period in 2025, representing a 13.1% decrease (522 fewer cases). Despite this year-over-year reduction, current weekly case counts remain elevated and consistent with typical late-winter varicella transmission patterns. Varicella (chickenpox), caused by varicella-zoster virus, is highly contagious with secondary attack rates exceeding 90% among susceptible household contacts. Transmission occurs through respiratory droplets and aerosols from respiratory secretions and through direct contact with vesicular fluid from skin lesions. The incubation period ranges from 10-21 days (typically 14-16 days), with infectivity beginning 1-2 days before rash onset and continuing until all lesions have crusted over, usually 5-7 days after rash appearance.
Scarlet fever, caused by Group A Streptococcus (Streptococcus pyogenes) producing erythrogenic toxins, was reported in 63 cases during Week 6, representing a slight decrease of 3 cases (4.5%) compared to Week 5. Of the 63 cases, 14 were classified as possible, 22 as probable, and 27 as confirmed. Year-to-date through Week 6, Bulgaria has registered 342 scarlet fever cases compared to 558 during the same period in 2025, representing a substantial 38.7% decrease (216 fewer cases). This marked reduction continues favorable trends observed throughout early 2026 and may reflect multiple factors including natural fluctuations in Group A Streptococcus strain circulation, possible effects of increased antibiotic use during the respiratory virus season treating bacterial complications or co-infections, changes in healthcare-seeking behavior, or reporting variations.
Scarlet fever presents with sudden onset of fever, sore throat, headache, and characteristic sandpaper-textured erythematous rash that typically begins on the chest and abdomen before spreading to extremities, with circumoral pallor and strawberry tongue as distinctive features. The disease predominantly affects children aged 5-15 years and transmits through respiratory droplets and direct contact with respiratory secretions. While generally self-limiting with appropriate antibiotic therapy, Group A Streptococcus can cause suppurative complications including peritonsillar abscess, cervical lymphadenitis, otitis media, and sinusitis, as well as non-suppurative post-infectious complications including acute rheumatic fever (which can lead to chronic rheumatic heart disease) and acute post-streptococcal glomerulonephritis. The decline in scarlet fever cases is epidemiologically favorable, though continued surveillance remains important given the potential for serious complications and the periodicity of invasive Group A Streptococcus infections.
Respiratory and Droplet Transmission
COVID-19 Activity Declines; Pertussis Remains Suppressed
COVID-19 cases decreased substantially during Week 6, with 22 confirmed cases reported representing a 38.9% decline (14 fewer cases) compared to the 36 cases reported in Week 5. All reported cases were laboratory-confirmed through PCR or rapid antigen testing. Year-to-date through Week 6, Bulgaria has registered 237 COVID-19 cases compared to 192 during the same period in 2025, representing a 23.4% increase (45 additional cases). However, this year-over-year comparison should be interpreted cautiously given dramatically reduced testing volumes, changes in testing indications focusing primarily on hospitalized patients and high-risk individuals, and evolution of surveillance systems from comprehensive case detection toward sentinel monitoring during the endemic phase of SARS-CoV-2 circulation.
The 38.9% week-over-week decrease likely reflects multiple factors including genuine reduction in transmission intensity, decreased healthcare-seeking behavior for mild respiratory illness as the post-holiday period progresses, and possible shifts in testing practices. Current SARS-CoV-2 circulation across the EU/EEA remains low relative to influenza and RSV, with limited hospitalizations attributable to COVID-19. Variant surveillance data from limited sequencing across Europe shows XFG as the dominant circulating variant, with emerging variant BA.3.2 detected at low but increasing proportions in some countries. While population-level hybrid immunity (from prior infections and vaccination) provides substantial protection against severe disease, older adults, immunocompromised individuals, and those with underlying conditions remain at risk for severe outcomes and should be prioritized for vaccination, particularly with updated formulations targeting currently circulating variants.
Pertussis (whooping cough) surveillance reported zero cases during Week 6, unchanged from Week 5. Year-to-date through Week 6, Bulgaria has registered only 3 pertussis cases compared to 23 during the same period in 2025, representing an 87.0% decrease (20 fewer cases). This dramatic reduction continues the favorable trend observed throughout early 2026 and contrasts sharply with several other EU/EEA countries reporting elevated or increasing pertussis activity. Pertussis, caused by Bordetella pertussis, manifests with paroxysmal cough, inspiratory whoop, and post-tussive vomiting, with the catarrhal stage (when patients are most contagious but symptoms are mild and nonspecific) preceding the characteristic paroxysmal stage by 1-2 weeks. Infants, particularly those too young to have received complete primary vaccination series, face highest risk for severe disease including apnea, pneumonia, seizures, encephalopathy, and death.
The sustained low pertussis activity in Bulgaria may reflect multiple factors including maintenance of high routine vaccination coverage preventing sustained transmission, favorable epidemiological phase in natural pertussis cycles (which demonstrate 3-5 year periodicity), possible under-recognition or under-reporting of cases given nonspecific presentation during catarrhal stage, or reduced testing. Despite current low activity, pertussis represents an important vaccine-preventable disease requiring continued surveillance vigilance. Healthcare providers should maintain clinical suspicion for pertussis in patients presenting with prolonged cough (>2 weeks) particularly if paroxysmal, and should ensure testing of suspected cases to enable appropriate treatment, contact management, and surveillance. Vaccination programs must sustain high coverage with primary infant series and recommended booster doses during adolescence and adulthood to maintain population immunity.
Bloodborne Transmission
Contact and Sexual Transmission
Gonorrhea Shows Substantial Year-Over-Year Increase
Gonorrhea cases totaled 7 during Week 6, representing an increase of 3 cases (75.0%) compared to the 4 cases reported in Week 5. All 7 cases were laboratory-confirmed through nucleic acid amplification testing or culture. Year-to-date through Week 6, Bulgaria has registered 23 gonorrhea cases compared to 7 during the same period in 2025, representing a 228.6% increase (16 additional cases). This substantial year-over-year elevation raises concern about potential increases in unprotected sexual activity, gaps in sexually transmitted infection prevention services, or changes in screening practices that may be detecting previously undiagnosed infections.
Gonorrhea, caused by the Gram-negative diplococcus Neisseria gonorrhoeae, ranks among the most common bacterial sexually transmitted infections globally. Transmission occurs through unprotected vaginal, anal, or oral sexual contact with an infected partner, with infectivity risk per exposure depending on anatomical site (urethral, cervical, rectal, pharyngeal), sexual practices, and possibly bacterial strain characteristics. Infection manifests differently by anatomical site and sex. In males, urethral infection typically causes purulent urethral discharge and dysuria within 2-7 days post-exposure, though asymptomatic urethral infection occurs in approximately 10% of cases. In females, cervical infection frequently remains asymptomatic (up to 50% of cases) or causes nonspecific symptoms including vaginal discharge, dysuria, intermenstrual bleeding, or lower abdominal discomfort, leading to delayed diagnosis and treatment. Rectal infection, which can occur through receptive anal intercourse or autoinoculation, often remains asymptomatic though may cause anorectal discomfort, discharge, or bleeding. Pharyngeal infection, transmitted through oral sexual contact, typically remains asymptomatic and may serve as an important reservoir for ongoing transmission.
Untreated gonorrhea can lead to serious complications. In females, ascending infection causes pelvic inflammatory disease (PID) in approximately 10-20% of untreated cervical infections, manifesting with lower abdominal pain, fever, and abnormal vaginal discharge. PID can result in chronic pelvic pain, ectopic pregnancy, and tubal factor infertility. In males, epididymitis represents the most common local complication, presenting with testicular pain and swelling. Disseminated gonococcal infection, occurring in 0.5-3% of untreated cases, manifests as arthritis-dermatitis syndrome with migratory polyarthralgia, tenosynovitis, dermatitis with pustular skin lesions, and occasionally septic arthritis or, rarely, endocarditis or meningitis. Neonates born to mothers with untreated gonorrhea face risk of ophthalmia neonatorum, which can cause blindness without prompt treatment.
The 228.6% year-over-year increase in gonorrhea warrants enhanced surveillance and public health response. Detailed case investigation should characterize demographic profiles of affected individuals, geographic distribution, sexual networks, and antimicrobial susceptibility patterns of isolated strains. Particular attention should focus on antimicrobial resistance, as N. gonorrhoeae has progressively developed resistance to successive classes of antimicrobials including sulfonamides, penicillins, tetracyclines, fluoroquinolones, and, most recently, extended-spectrum cephalosporins. Current treatment recommendations in most settings rely on dual therapy combining ceftriaxone (250-500 mg intramuscularly) with azithromycin (1-2 grams orally), though resistance patterns continue to evolve. Public health interventions should emphasize sexually transmitted infection screening particularly for high-risk populations including individuals with multiple sexual partners, men who have sex with men, and young adults; promotion of consistent and correct condom use; partner notification and treatment; and linkage to comprehensive sexual health services including HIV and other STI testing.