Epidemiological News: Week 25, 2026

Week 25 of 2026 (15–21 June) is dominated by an escalation in the Bundibugyo virus Ebola disease outbreak in the Democratic Republic of the Congo, where confirmed cases rose from 676 to 896 over the reporting period—a 220-case increase attributed substantially to clearance of a diagnostic testing backlog—while the case fatality ratio held near 26% and the outbreak’s geographic footprint expanded to 33 of 104 health zones across Ituri, North Kivu, and South Kivu. Uganda’s linked outbreak has shown no new cases since 5 June, suggesting the imported chain there may be approaching containment even as the DRC epicentre continues to grow. A new avian influenza A(H9N2) human case in Hong Kong, confirmed by whole-genome sequencing as an avian-origin virus with no household transmission, adds to the global avian influenza landscape, alongside WOAH notifications of a first-ever H5N1 detection in Australian wild birds and continuing New World screwworm spread in Mexico and the United States. In the non-communicable disease domain, two large randomised trials (JAMA, NEJM) returned null results for sodium bicarbonate in cardiac arrest and critical illness, while a major Lancet analysis of 23 years of English mortality data attributed a 100% reduction in cervical cancer deaths among HPV-vaccinated women aged 20–24. In Bulgaria, gonorrhea notifications resumed sharply (eight cases, up from zero in Week 24), sustaining a 177% year-to-date excess over 2025, while the ongoing measles outbreak added 22 cases via regional surveillance, concentrated as before in Vratsa, Pleven, and Lovech districts; acute viral hepatitis, campylobacteriosis, and urogenital chlamydial infection all continued to track substantially above their 2025 baselines, even as scarlet fever and pertussis remained well below last year’s levels.
English
Author

Kostadin Kostadinov

Published

June 24, 2026

Non-Communicable Disease and Healthcare System Developments

Recent Research Highlights: Sodium Bicarbonate in Acute Care

Two independent randomised trials published this period converge on a consistent null finding for sodium bicarbonate administration in critically ill adults, a clinically significant result given the drug’s continued widespread empirical use. The Danish in-hospital cardiac arrest trial (JAMA), enrolling 779 evaluable patients with in-hospital cardiac arrest across 21 hospitals, found sustained return of spontaneous circulation in 39% of patients receiving sodium bicarbonate versus 37% receiving placebo (risk ratio 1.05, 95% CI 0.88–1.24)—a difference well within the bounds of chance. Thirty-day survival favoured the bicarbonate arm numerically (12% versus 9.1%) but the confidence interval was wide and compatible with no effect (risk ratio 1.25, 95% CI 0.84–1.88), and alkalosis and hypernatremia occurred more frequently with bicarbonate, reinforcing a recognised harm profile without a compensating benefit signal. The companion SODa-BIC trial (NEJM), a pragmatic adaptive trial spanning 55 intensive care units across seven countries and enrolling 500 patients with metabolic acidosis on vasopressors, similarly found no reduction in major adverse kidney events at 30 days (40.2% bicarbonate versus 39.4% placebo; adjusted difference 1.2 percentage points, 95% CI −7.1 to 9.4) and no mortality benefit (25.4% versus 24.0%). Taken together, these trials—conducted in markedly different clinical populations (in-hospital arrest versus vasopressor-dependent metabolic acidosis)—provide convergent, well-powered evidence against routine sodium bicarbonate administration in either setting, and should inform resuscitation and intensive care protocols that have historically included bicarbonate as a default intervention for acidemia correction.

HPV Vaccination and Cervical Cancer Mortality — England, 2001–2024

A population-based analysis published in The Lancet provides what its authors describe as the first robust national-level evidence that high-coverage HPV vaccination is associated with a substantial reduction in cervical cancer mortality, extending prior incidence-based findings into mortality outcomes. Using English national mortality data for women aged 20–34 years from 2001 to 2024, linked to birth-cohort vaccination coverage records, the analysis found that among women aged 20–24 in 2020–2024—who had received the vaccine at age 12–13 with 88–90% coverage—zero cervical cancer deaths occurred against 23.1 expected based on historical rates, corresponding to a 100% mortality reduction (95% CI 84–100%). Earlier birth cohorts offered vaccination later (up to age 18, with lower coverage of 63–87%) showed smaller but still substantial reductions: 80% in women aged 20–24 in 2015–2019 and 69% in those aged 25–29 in 2020–2024. Across the analysis period, HPV vaccination is estimated to have averted approximately 199.6 cervical cancer deaths (95% CI 125.0–274.2) in England. The gradient by vaccination age and coverage—larger mortality reductions in cohorts vaccinated earlier and at higher coverage—is mechanistically coherent with HPV natural history, in which vaccination before sexual debut prevents the initial high-risk HPV infections that drive the decades-long progression to invasive cancer, and provides observational but methodologically robust support for the WHO cervical cancer elimination target. The finding carries direct relevance for Bulgaria’s own HPV immunisation programme, where coverage has historically lagged the EU/EEA average, underscoring the long-term mortality cost of incomplete catch-up vaccination among adolescent cohorts.


Infectious Diseases: Global Perspective

Contact and Bloodborne Transmission

Ebola Disease Outbreak (Bundibugyo Virus) — Democratic Republic of the Congo and Uganda

The Bundibugyo virus disease (BVD) outbreak in the Democratic Republic of the Congo registered its largest single-period increase since WHO’s 17 May declaration of a Public Health Emergency of International Concern. According to WHO’s 19 June Disease Outbreak News, cumulative confirmed cases in DRC rose from 676 as of 13 June to 896 as of 17 June—an increase of 220 cases and 96 deaths in four days—bringing the cumulative total to 232 deaths (case fatality ratio 26%, almost certainly an underestimate given that many pre-declaration deaths remain under investigation). WHO attributes a substantial portion of this increase to expanded laboratory testing capacity clearing a backlog of previously collected, unprocessed samples, meaning the apparent acceleration partly reflects improved case ascertainment rather than purely new transmission; nonetheless, the outbreak’s geographic footprint has also genuinely expanded, with 33 of 104 health zones now affected across Ituri (21/36), North Kivu (11/35), and South Kivu (1/34) provinces, including two newly reporting zones (Fataki and Musienene) identified in mid-June. Ituri remains the epicentre, accounting for 91.1% of confirmed cases (817 of 896) with a province-specific CFR of 22.7%, concentrated in Bunia (247 cases), Rwampara (195), Mongbwalu (189), and Nyankunde (68) health zones. Contact tracing follow-up stood at 70.8% in Ituri and 70.5% in North Kivu as of 17 June—below the threshold generally considered adequate for outbreak control—against a backdrop of active armed conflict and population displacement that WHO explicitly identifies as constraining response access and elevating the risk of undetected transmission chains. ECDC’s most recent assessment (18 June) places the cumulative DRC count slightly lower, at 875 confirmed cases and 202 deaths as of 16 June, reflecting the one-to-two-day reporting lag characteristic of WHO–ECDC cross-referencing during a rapidly evolving event; both sources agree on the trajectory and the underlying drivers.

In Uganda, by contrast, the linked outbreak shows early signs of containment: the cumulative case count stood at 19 confirmed cases (two deaths) and one probable case (one death) as of 18 June, unchanged in new-case terms since 5 June—now a fortnight without a new confirmed case. Of the 19 confirmed cases, 14 were directly travel-linked to DRC and five represented secondary transmission among contacts and healthcare workers, with no documented community transmission to date; cases remain confined to Kampala and Wakiso districts, both within the Kampala Metropolitan Area. Of 826 listed contacts, 694 have completed their 21-day follow-up period without developing disease, a reassuring proportion that supports the assessment of a contained, travel-associated cluster rather than sustained local transmission. One Ugandan case with travel history to the United Arab Emirates, arriving 24 May, has been the subject of coordinated risk assessment between WHO and UAE authorities; no Ebola cases have been detected in the UAE to date, an important point of reassurance given the case’s air-travel link, though it also illustrates the outbreak’s continued potential for wider geographic reach via international travel corridors. Several symptomatic travellers from affected areas have been tested in both EU/EEA and non-EU/EEA countries during this reporting period, all returning negative results.

Clinically, BVD shares the general Ebola disease presentation—an incubation period of two to 21 days, followed by non-specific early symptoms (fever, fatigue, myalgia, headache, sore throat) that progress to gastrointestinal symptoms, organ dysfunction, and, in a subset of cases, haemorrhagic manifestations—but carries case fatality ratios that have historically varied more widely between BVD outbreaks (30% in Uganda 2007, 50% in DRC 2012) than is typical for Zaire ebolavirus. As previously documented in this report series, Bundibugyo virus—genomically distinct from the more familiar Zaire ebolavirus, against which both a licensed vaccine and monoclonal antibody therapeutics exist—has no licensed vaccine or specific antiviral treatment, a gap that continues to constrain outbreak response options to case isolation, contact tracing, safe burial practices, and infection prevention and control, with transmission amplified wherever these IPC measures are inadequate, including within healthcare settings. ECDC maintains its assessment that the likelihood of infection for EU/EEA residents is low for those travelling to or living in affected areas and very low for the general EU/EEA population, while explicitly noting that the true outbreak size in DRC is probably larger than currently reported, given persistent contact-tracing gaps and the constrained operational environment of an active conflict zone with substantial population displacement. ECDC additionally assesses the overall risk of Bundibugyo virus transmission through substances of human origin (blood, tissue, and cell donations) in the EU/EEA as very low, and continues to advise against screening of returning travellers from DRC or Uganda as an effective importation-prevention measure, citing the lessons of the 2013–2016 West African Ebola epidemic; priority is instead placed on equipping travellers with clear post-arrival symptom guidance. Since 19 May, the EU Health Task Force has deployed ECDC experts on rotation to Africa CDC headquarters in Addis Ababa, with a further group of three ECDC and two member state experts deployed on 15 June to Kinshasa and Kampala to assess exit screening strategies at points of entry, and a risk communication and community engagement expert deployed on 16 June to the WHO country office in Juba, South Sudan, reflecting concern about onward spread risk into neighbouring countries.

Respiratory and Droplet Transmission

Avian Influenza A(H9N2) — Hong Kong

Whole-genome sequencing confirmed on 15 June that a child in Hong Kong’s Sha Tin District, hospitalised since 10 June with mild fever and diarrhoea, is infected with low-pathogenic avian influenza A(H9N2) virus showing no significant genetic variation from previously characterised strains—that is, no markers suggestive of enhanced mammalian adaptation or transmissibility. The patient, with no known comorbidities, had no travel history during the incubation period and is classified as a locally acquired, market-associated infection: exposure is attributed to two visits to a live poultry shop, where environmental sampling subsequently identified A(H9) virus on a metal tray beneath a chicken cage. All six household contacts and shop staff remain asymptomatic, and no additional cases have been identified through contact follow-up, indicating an isolated zoonotic spillover event without onward transmission. Avian influenza A(H9N2), endemic in poultry across parts of Asia, has produced 207 cumulative human cases and two deaths globally since 1998 (CFR approximately 1%), almost exclusively following direct or market-associated contact with infected birds; sustained human-to-human transmission has never been documented. ECDC assesses the risk to EU/EEA human health as very low, consistent with the absence of any sustained transmissibility marker in this isolate and the case’s clear point-source poultry market exposure.

Vector-Borne and Zoonotic Transmission — WOAH Animal Disease Notifications

Two World Organisation for Animal Health (WOAH) notifications carry direct relevance beyond routine veterinary surveillance. Australia reported its first-ever detection of highly pathogenic avian influenza A(H5N1) in wild birds on 15 June, representing the introduction of this globally dominant clade into a continent that had, until this point, remained one of the few largely unaffected by the current H5N1 panzootic; given H5N1’s established capacity for spillover into mammalian species (including, rarely, humans), first detections in previously unaffected geographies warrant monitoring even where, as here, the initial notification concerns wild birds rather than poultry or livestock. Separately, New World screwworm (Cochliomyia hominivorax)—a myiasis-causing parasitic fly historically eradicated from North America through a decades-long sterile-insect release programme—continues its documented northward spread, with the United States reporting recurrence on 2 June 2026 and Mexico reporting two further first-occurrence notifications in April and June 2026. This progressive re-establishment in the southern United States and Mexico, following the species’ return to Central America in recent years, represents a genuine reversal of a major 20th-century eradication achievement with direct livestock and, less commonly, human health implications, and is being tracked by USDA and Mexican agricultural authorities as a re-emerging threat distinct from the routine background of avian influenza and African swine fever notifications that otherwise dominate the WOAH weekly disease event list.


Infectious Diseases: European Union/European Economic Area

Vector-Borne Transmission

Seasonal West Nile Virus Surveillance — Season Onset

ECDC’s weekly seasonal West Nile virus (WNV) surveillance report, now active for the 2026 transmission season, recorded three human cases from two countries as of 17 June: Italy and North Macedonia. This represents the formal start of the EU/EEA’s WNV reporting season, against which subsequent weeks’ case accumulation should be benchmarked; ECDC explicitly assesses that seasonal weather conditions are currently favourable for Culex mosquito-borne transmission and anticipates rising case counts through the coming weeks, consistent with the typical June–October transmission window for WNV in southern and southeastern Europe. WNV, a flavivirus maintained in a bird–mosquito enzootic cycle with humans as incidental dead-end hosts, causes asymptomatic or mild febrile illness in the large majority of infections, with neuroinvasive disease (meningitis, encephalitis, or acute flaccid paralysis) in less than 1% of infections, disproportionately among individuals over 60 years of age or immunocompromised. WNV is also notifiable under EU blood-safety directives, which require 28-day donor deferral following travel from an active transmission risk area; this regulatory mechanism makes the weekly ECDC risk-area map directly operationally relevant to national blood establishments, including in Bulgaria, where no autochthonous WNV cases have yet been reported in 2026 (noted in the national section below) but where the country’s documented history of WNV circulation means the early-season EU/EEA picture should inform heightened vigilance as the season progresses.

One Health: Animal Disease Events in the European Region

Several WOAH notifications from EU/EEA member states this period illustrate the continuing, largely background circulation of multiple zoonotic and livestock pathogens rather than a discrete new threat. Croatia reported the first occurrence of peste des petits ruminants virus in the country (notified 19 June, with onset retrospectively dated to December 2025), marking the entry of this small-ruminant morbillivirus—of no direct human health relevance but of substantial agricultural and food-security significance—into a previously unaffected EU member state. Ireland reported its first occurrence of bluetongue virus serotype 3 in the country, alongside recurrence of H5N1 highly pathogenic avian influenza, while African swine fever continued its persistent recurrence pattern across Poland, Romania, Estonia, Latvia, Croatia, and Hungary, reflecting the entrenched endemic circulation of this swine pathogen in central and eastern Europe that has characterised WOAH reporting throughout 2026. None of these events carry direct human health implications under current epidemiological understanding, but they are flagged here under the One Health framework given their relevance to agricultural biosecurity policy and, in the case of avian influenza, their contribution to the broader reservoir from which sporadic human spillover events (such as the Hong Kong A(H9N2) case discussed above) ultimately arise.


Infectious Diseases: Bulgaria

Respiratory and Droplet Transmission

Measles

Regional ZRZ/NCOZA surveillance recorded 22 measles cases in Week 25, a reporting-architecture figure that—as established throughout this report series—is not captured in the NCIPD national operational analysis, which shows no measles entries for the week. District attribution from the regional table shows continued concentration in the established outbreak core: Vratsa (8 cases), Pleven (7), Lovech (3), Ruse (2), and Sofia-grad (1), with one case not individually attributable in the published breakdown. This pattern sustains the geographic distribution documented in ECDC’s most recent monthly measles monitoring (Weeks 23–24), which identified Vratsa, Pleven, and Lovech as accounting for 93% of Bulgaria’s cumulative 2026 outbreak caseload, with Bulgaria ranking second among EU/EEA reporting countries by total case count. The appearance of cases in Ruse, a Danube-border district outside the three-district outbreak core, merits continued attention as a potential marker of geographic spread beyond the established northwestern/north-central focus, consistent with this report series’ standing practice of flagging geographic expansion as a significant signal independent of week-to-week case count trends. As previously detailed, measles (Morbillivirus hominis) transmits via the respiratory/airborne route with an R₀ of 12–18, the highest of any common human pathogen, requiring sustained two-dose MMR coverage above 95% to interrupt transmission; the documented predominance of unvaccinated cases in the outbreak to date indicates the underlying immunity gap in the affected districts remains the principal driver of continued transmission, and case-based investigation with targeted catch-up immunisation in Vratsa, Pleven, and Lovech—now extending to neighbouring districts—remains the priority response measure.

Contact and Sexual Transmission

Gonorrhea

Gonorrhea notifications resumed sharply in Week 25 with eight confirmed cases, following a single week (Week 24) with no reported cases—an eight-case increase that, while derived from small absolute numbers, restores the trajectory of sustained excess that has characterised this indicator throughout 2026. The year-to-date cumulative total reached 119 cases by Week 25, a 177% excess over the 43 cases recorded in the same period of 2025, continuing to represent the most pronounced year-over-year deviation among nationally tracked sexually transmitted infections. As previously noted in this report series, routine Bulgarian gonorrhea surveillance does not capture antimicrobial susceptibility data, a limitation of particular consequence given the global emergence of extensively drug-resistant Neisseria gonorrhoeae strains and the resulting risk that treatment failures could go undetected within current national surveillance architecture.

Urogenital Chlamydial Infection

Urogenital chlamydial infection registered eight cases in Week 25 (a three-case, 60% increase from Week 24), with the year-to-date cumulative total of 172 cases now 139% above the 72 cases recorded in the same period of 2025. Chlamydia trachomatis remains the most frequently reported bacterial sexually transmitted infection across the EU/EEA and is commonly asymptomatic, particularly in women, producing a structural undercount in passive surveillance systems irrespective of true transmission intensity; the sustained, large excess documented across 2026 to date most plausibly reflects some combination of genuine increased transmission and improved case ascertainment, a combination that cannot be disentangled using routine notification data alone but which, given its persistence across more than twenty consecutive weeks of this report series, warrants continued monitoring as a structural rather than transient feature of the 2026 surveillance year.

Acute Viral Hepatitis (ABCDEN)

Acute viral hepatitis ABCDEN registered 31 cases in Week 25 (an 11-case, 26% decrease from the 42 cases reported in Week 24), the first substantial single-week decline after two consecutive weeks of increase. Despite this decline, the year-to-date cumulative total of 905 cases remains 55% above the 585 cases recorded in the same period of 2025, sustaining what continues to be the most consistent and largest-magnitude surveillance excess documented in this report series across 2026. The single-week decline should not be interpreted as a reversal of the underlying trend given the persistence and scale of the cumulative excess; as previously noted, the aggregate ABCDEN reporting category precludes serotype-specific attribution, which continues to constrain the ability to distinguish faecal-oral hepatitis A dynamics from bloodborne hepatitis B/C transmission—each implying a substantially different public health response—and the magnitude of this now five-month sustained excess continues to justify formal epidemiological review with serotype disaggregation of confirmed cases.

Vector-Borne Transmission

Campylobacteriosis

Campylobacteriosis registered nine cases in Week 25 (a one-case decrease from Week 24), with the year-to-date cumulative total of 269 cases now 63% above the 165 cases recorded in the same period of 2025. This sustained year-over-year excess, evident consistently across the 2026 surveillance year to date, is consistent with Campylobacter’s established seasonal peak in late spring and summer, when warmer temperatures favour environmental persistence and food-handling-associated transmission; the magnitude of the excess relative to 2025, however, exceeds what would be expected from seasonality alone and may reflect either a genuine increase in foodborne exposure (commonly undercooked poultry or contaminated water) or improved laboratory ascertainment, neither of which can be distinguished from aggregate notification counts. Unlike salmonellosis, which has tracked closely with its 2025 baseline throughout the year, campylobacteriosis has now sustained a substantial excess for several consecutive months, a divergence between the two principal bacterial gastroenteritis pathogens under national surveillance that merits separate epidemiological characterisation rather than being subsumed within a generic foodborne-illness narrative; the absence of routine serotyping or source-attribution data in Bulgarian notification surveillance, however, limits further interpretation of whether this reflects a specific point-source exposure pathway or a broader shift in poultry-associated food safety practices.