Through event-based surveillance performed throughout 2019, WHO became aware of a dengue outbreak in Mayotte, France, since July 2019. According to the local health authority (Agence Régionale de Santé) of Mayotte, dengue cases were reported since March 2019; however, the epidemic intensified during January 2020 when the number of cases increased significantly.
From the beginning of January 2020 to 17 April 2020, 3533 confirmed cases of dengue fever have been reported on the island, including 16 deaths. Of the 3533 cases, 339 were hospitalized and 21 cases were managed in intensive care units. From 23 February 2020 to 21 March 2020, six out of 17 communes in Mayotte had an incidence rate of more than 5%.
The vast majority of the dengue cases in this outbreak have been caused by dengue virus serotype 1 (DENV-1).
In the past, Mayotte has reported four dengue outbreaks, in 1993, 2010 (caused by DENV-3), and in 2013 and 2014 (caused by DENV-2), which were recorded in several communes of the main island of Mayotte and the small island of Petite-Terre. The current outbreak is the largest outbreak of dengue in Mayotte reported to date. Prior to this, the largest outbreak was recorded in 2014 with 522 laboratory confirmed cases, of which 494 cases were confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and 27 were confirmed by serologic tests. During the 2014 outbreak, only serotype DENV-2 was identified.
Public health response
Health authorities in Mayotte have implemented the following measures:
- Strengthening integrated vector control activities;
- Enhancing surveillance to identify cases;
- Updating clinical management guidelines, social mobilization and emergency risk communications.
WHO risk assessment
Mayotte Island is part of the Comoros archipelago (Mozambique Channel, southwestern Indian Ocean), which is under French administration. Since 2019, only circulation of DENV-1 has been established in Mayotte. However, epidemics caused by other serotypes are currently underway in the Indian Ocean area, making it possible for another serotype to be introduced to Mayotte. A shift in the predominant DENV serotype may result in more severe secondary dengue virus infections and severe dengue cases requiring hospitalization and good case management. A comprehensive risk communication should be developed.
Due to the presence and sufficient density of the competent vectors (Aedes albopictus and Aedes aegypti), hot and humid climate, and the current rainy season (tropical maritime climate with a hot rainy season from November to May), further upsurge in cases cannot be ruled out.
Responding to the dengue outbreak in Mayotte might be challenging due to the current coronavirus disease 2019 (COVID-19) situation and overwhelmed health care facilities. As of 18 April 2020, Mayotte reported 263 confirmed cases of COVID-19. Furthermore, it is possible that some of the population, might have difficulty accessing the health system. The population in Mayotte is young but includes vulnerable populations, such as economically disadvantaged people, racial and ethnic minorities, those who are uninsured, and individuals with chronic health conditions such as diabetes and hypertension, who often encounter barriers to accessing healthcare services.
Mayotte only has one hospital and 16 beds in the intensive care unit, and recourse to traditional medicine is also frequent. Additionally, underreporting of dengue cases cannot be excluded.
There is no specific treatment for dengue. However, timely detection of cases, identifying any warning signs of severe cases of dengue, and appropriate early case management are key elements of care to prevent deaths due to dengue. A delay in seeking medical care in severe dengue cases is often related to deaths from dengue virus disease. Outer islands should refer cases or seek help as early as possible.
Additionally, Integrated Vector Management (IVM) activities should be enhanced to remove potential breeding sites, reduce vector populations, and minimize individual exposure. This should include both larval and adult vector control strategies (i.e. environmental management and source reduction and chemical control measures). Vector control measures should be implemented at households, places of work, schools, and healthcare facilities, among others, to prevent vector-person contact.
Given that Aedes mosquitoes, the competent vector, has greater activity during the day, personal protection measures are recommended, such as wearing protective clothing that minimizes skin exposure and using repellents that can be applied to exposed skin or clothes strictly as instructed on the label. Window and door screens, and mosquito nets (impregnated or not with insecticide) can be useful to reduce vector-person contact in closed spaces during the day or night.
Community supported source reduction measures should be initiated, and vector surveillance and control implemented. During lockdown situations due to COVID-19, households should be encouraged to work together in and around their homes to remove stagnant water, reduce solid wastes and to ensure proper covering of all water storage containers. This can be done as a weekly family activity and will help lower the density of mosquitoes.
WHO does not recommend any restrictions on travel or trade to Mayotte on the basis of the information available on this outbreak.