Research and analysis

Outbreaks under monitoring: week 37 (week ending 14 September 2025)

Updated 18 September 2025

Disease or pathogen	Dengue
Location	Samoa
Reporting date	9 September 2025
Summary	On 17 April 2025, the Samoa Ministry of Health declared a dengue fever outbreak following a substantial increase in the number of recorded dengue cases. Between 1 January and 31 August 2025, 12,025 clinically diagnosed dengue cases (including 3,630 confirmed cases) and 6 deaths have been reported in Samoa. 73% of cases have been reported in children aged under 15 years. This is an increase of 1,043 clinically diagnosed dengue cases (including 251 confirmed cases) since the last report on 26 August 2025. There is no current evidence of local transmission of dengue virus in the United Kingdom (UK) and there is no evidence of established populations of the mosquito responsible for dengue transmission. Most reported UK cases have been related to travel abroad.
Further information	Dengue fever: guidance, data and analysis Travel-associated infections reports NaTHNaC country information page: Samoa

Disease or pathogen	Ebola virus disease
Location	Democratic Republic of the Congo (DRC)
Reporting date	4 to 14 September 2025
Summary	On 4 September 2025, the DRC’s Ministry of Health reported an outbreak [in French] of Ebola virus disease (EVD) in Bulape health zone, Kasai Province. This is the sixteenth EVD outbreak reported in the DRC. As of 14 September 2025, 65 EVD cases (including 25 confirmed and 40 suspected cases) and 24 deaths (case fatality rate of 36.9%) have been reported from Bulape health zone, Kasai Province. On 14 September 2025, the World Health Organization (WHO) reported that the vaccination of frontline health workers and contacts of EVD cases has begun in Bulape health zone. According to the WHO, 400 doses of the Ervebo vaccine from the country’s stockpile of 2,000 doses have been delivered to Bulape health zone and will be administered through a ring vaccination strategy. On 14 September 2025, media reported that treatment using Ebanga [in French], a monoclonal antibody medication, has commenced in Bulape health zone. WHO assesses the public health risk of this outbreak as high at the national level, moderate at the regional level and low at the global level. Imported cases of Ebola disease (EBOD) are very rare in the UK. Four confirmed cases of EBOD, and no deaths, have been previously reported in the UK. The last reported confirmed case of EBOD in the UK was in 2014
Further information	Ebola: overview, history, origins and transmission Ebola virus disease: clinical management and guidance Ebola and Marburg haemorrhagic fevers: outbreaks and case locations NaTHNaC country information page: Democratic Republic of the Congo.

Disease or pathogen	Legionella
Location	Canada
Reporting date	9 September 2025
Summary	On 8 July 2025, the Middlesex-London Health Unit declared an outbreak of legionnaires’ disease in London, Ontario, Canada. Between 1 January and 9 September 2025, 105 cases of Legionnaires’ disease (including 5 deaths) have been reported in the ongoing outbreak. The cases reported in this outbreak represent 41.8% of all Legionnaires’ disease cases recorded in Ontario between 1 January and 10 September 2025 (249 cases). In the UK, reported Legionnaires’ disease cases follow a seasonal pattern, with a peak number typically reported between June and October. Between 2017 and 2023, 3,276 cases of Legionnaires’ disease were reported in the UK. In 2023, 212 of 604 confirmed Legionella exposures (35.1%) were related to travel abroad.
Further information	Legionnaires’ disease: guidance, data and analysis NaTHNaC country information page: Canada

For more information on the background and methods used in this report, see Outbreaks under monitoring: background and methodology.