Research and analysis

Outbreaks under monitoring: week 18 (week ending 3 May 2026)

Updated 8 May 2026

Disease or pathogen	Avian influenza A(H5N1)
Location	Bangladesh
Status	New
Reporting date	29 April 2026
Summary	On 29 April 2026, the World Health Organization (WHO) shared information regarding a fatal human case of avian influenza A(H5N1) infection in Chattogram Division, Bangladesh. The case was a child with no known comorbidities who experienced symptom onset on 21 January 2026. The case was hospitalised a week later before being admitted to intensive care on 31 January 2026 and succumbing to illness on 1 February 2026. The Bangladesh Institute of Epidemiology, Disease Control and Research confirmed samples from the case tested positive for avian influenza A(H5N1) clade 2.3.2.1a, a similar clade to those reported to be circulating in local poultry since 2011. The case had exposure to household poultry which had died prior to the case’s symptom onset. Laboratory testing of poultry in the case’s community and household freezer tested positive for avian influenza A(H5). This is the first reported human case of avian influenza A(H5) in Bangladesh in 2026. During 2025, 4 cases were reported .
Further information	Avian influenza: managing human exposures to incidents in birds or animals NaTHNaC country information page: Bangladesh

Disease or pathogen	Severe fever with thrombocytopaenia syndrome (SFTS)
Location	Japan and South Korea
Status	Update
Reporting date	28 April to 3 May 2026
Summary	On 28 April 2026,  Japan’s Institute for Health Security reported 16 confirmed cases of SFTS across 10 prefectures in 2026, up to 19 April. The highest number of cases have been reported from Saga (3 cases) and Oita (3 cases) prefectures. During 2025, 191 cases were reported across Japan. As of 3 May 2026, South Korea’s Disease Control and Prevention Agency has reported 3 confirmed cases of SFTS in 2026. All cases have been identified as locally acquired from Gangwon, Ulsan, and Gyeongnam regions. During 2025, 280 cases were reported across South Korea, representing the highest annual number of reported cases in over a decade. The SFTS virus is not found in the UK, and no travel-associated cases have been reported in the UK to date.
Further information	Severe fever with thrombocytopaenia syndrome (SFTS): epidemiology, outbreaks and guidance. NaTHNaC country information page: Japan and South Korea

Disease or pathogen	Crimean-Congo haemorrhagic fever (CCHF)
Location	Iraq and Turkey
Status	New
Reporting date	29 April to 1 May 2026
Summary	On 29 April 2026, media (in Turkish) reported 2 human cases of CCHF in Tokat, Turkey. Both individuals had a history of tick exposure. Following hospitalisation, their clinical condition has reportedly improved. On 1 May 2026, media (in Arabic) reported 16 cases of CCHF, including 2 associated deaths, in Dhi Qar governorate, Iraq, since the start of 2026. In response, authorities have intensified awareness campaigns on transmission pathways of CCHF. Iraq and Turkey report cases of CCHF annually. CCHF is not present in the UK, nor are there any identified established populations of Hyalomma ticks, the principal vectors of CCHF virus. Confirmed CCHF cases have been imported into the UK, including one fatal case in 2012 and one in 2014.
Further information	Crimean-Congo haemorrhagic fever: origins, reservoirs, transmission and guidelines HAIRS risk assessment: Crimean-Congo haemorrhagic fever NaTHNaC country information page: Iraq and Turkey

Disease or pathogen	Poliovirus
Location	Australia
Status	New
Reporting date	1 May 2026
Summary	On 1 May 2026, the Australian Centre for Disease Control reported an environmental detection of circulating vaccine-derived poliovirus type 2 from a wastewater sample in Perth, Western Australia. In Australia, children are vaccinated using the inactivated poliovirus vaccine which does not cause vaccine-derived poliovirus. In response, authorities have organised follow-up weekly wastewater testing and surveillance for any related clinical signals. In 2026, up to 26 March, 2 unrelated environmental detections of vaccine-derived poliovirus type 2 have been identified in sewage samples taken in London, UK. As part of routine surveillance, single or very brief detections of ‘vaccine-like’ polioviruses are detected in UK sewage samples each year. These one-off or brief detections do not require any public health action.
Further information	Polio: guidance, vaccination, data and analysis NaTHNaC country information page: Australia

Disease or pathogen	Swine influenza
Location	Brazil and China
Status	New
Reporting date	29 April 2026
Summary	On 29 April 2026, WHO shared information regarding recently reported human cases of swine influenza A(H1N1)v and A(H1N2)v in China, and A(H3N2)v in Brazil. On 3 February 2026, China notified WHO of a confirmed human case of influenza A(H1N2)v infection in Yunnan province. The case is a child who experienced symptom onset of mild illness on 20 January 2026 and tested positive on 2 February 2026. Prior to illness onset, the case reported exposure to domestic pigs. On 20 March 2026, a confirmed human case of influenza A(H1N1)v infection was also reported in Yunnan province. The case involved a child who experienced symptom onset on 30 January 2026 and was hospitalised on 2 February 2026 with pneumonia. The child recovered within a few days. Prior to illness onset, the case reported exposure to domestic pigs. This case is not epidemiologically linked to the swine influenza A(H1N2)v case also reported in Yunnan Province. On 26 January 2026, Brazil notified WHO of a confirmed human case of influenza A(H3N2)v infection in Mato Grosso do Sul State. The case is a child who developed influenza-like symptoms on 1 September 2025, sought medical care on 2 September 2025, and tested positive on 12 September 2025. The case had no known comorbidities or recent travel history and received vaccination during the last seasonal influenza campaign. Epidemiological investigations identified the case to be a student at an agricultural school where pigs and laying hens are raised, however, the students had no recent direct contact with pigs. The case had contact with classmates experiencing influenza-like symptoms during the same period. No additional human cases of infection with influenza A(H3N2)v were detected in association with this case. The public health risk from current known influenza A viruses detected at the human-animal interface is assessed as low by WHO. Sustained human-to-human transmission of these viruses is currently considered unlikely.
Further information	Influenza A(H1N2)v: guidance for affected members of the public Influenza (avian and other zoonotic) NaTHNaC country information page: Brazil and China

The following signal relates to an ongoing outbreak, with data current to 6 May 2026.

Disease or pathogen	Andes hantavirus
Location	Argentina
Status	New
Reporting date	2 May 2026
Summary	On 2 May 2026, WHO was notified of a cluster of severe respiratory illness aboard a cruise ship carrying 147 passengers and crew from various countries. On 2 May 2026, laboratory testing of samples taken from a case confirmed hantavirus infection; this was later confirmed to be Andes hantavirus. The cruise ship departed from Ushuaia, Argentina, on 1 April 2026, and travelled across the South Atlantic, with stops in Antarctica, South Georgia, Nightingale Island, Tristan da Cunha, Saint Helena, and Ascension Island. On 4 May 2026, the ship anchored along the coast of Cape Verde (in Portuguese). As of 6 May 2026, 8 cases (3 confirmed and 5 suspected), including 3 deaths  have been reported. The index case experienced symptom onset on 6 April 2026 while onboard the ship and later died. This case, and a second case had travelled together around South America, including Argentina, prior to boarding the cruise ship on 1 April 2026. The second case disembarked the boat and experienced clinical deterioration during a flight to Johannesburg, South Africa, on 25 April 2026, where they later died. According to WHO, the outbreak is being managed through a coordinated international response, including the organisation of epidemiological investigations, case isolation and care, and medical evacuation. In response, WHO currently assesses the risk of this event to the global population to be low. Although rodent-associated hantavirus infections occur in the UK, there is no risk of Andes hantavirus infection in the UK. It is possible that rare, travel-associated infections may be seen in the UK in travellers returning from Argentina and Chile, although none have been reported to date. Human to human transmission is also known to be rare, although possible.
Further information	Andes hantavirus: epidemiology, outbreaks and guidance Hantaviruses: characteristics, diagnosis and epidemiology HAIRS risk assessment: hantavirus NaTHNaC country information page: Argentina