T he Republic of Djibouti, bordered by Eritrea, Ethiopia, and Somalia, is a semiarid country in the Horn of Africa. The population comprises <900,000 persons, 70% of whom live in Djibouti, the capital city. Before 2013, malaria was hypoendemic to the country, with low levels of transmission in periruban and rural areas during December-May. Localized outbreaks occurred regularly, possibly caused by migration from surrounding countries. Most cases were caused by infection with Plasmodium falciparum (>80%) or P. vivax. Before 2013, researchers considered the Anopheles arabiensis mosquito to be the primary vector (1).The incidence of malaria had drastically decreased in the country since 2008; by 2012, this transmission level was compatible with preelimination goals (2,3). In 2013, an autochthonous outbreak of malaria occurred in Djibouti; fi eld entomologic investigations identifi ed An. stephensi mosquitoes as a new malaria vector (4). This species, a known vector of urban malaria in India and the Arabian Peninsula, has changed the epidemiologic profi le of malaria in Djibouti (5). In 2018, malaria incidence increased to 25,319 confi rmed cases (64% caused by P. falciparum and 36% by P. vivax) and >100,000 suspected cases (Appendix Figure 1, https://wwwnc.cdc.gov/EID/ article/27/6/20-4557-App1.pdf).The French Armed Forces (FAF) have served in Djibouti for decades. Service members and their families (≈2,700 persons) live in the capital. Despite malaria prevention and treatment measures described elsewhere (6), an outbreak among French military personnel occurred in February 2019; failure of early artemisinin combined therapy was documented in 1 patient.
The StudyWe collated FAF epidemiologic surveillance data on malaria cases among service members in Djibouti during 1993Djibouti during -2019; the 2019 data included cases among family members. We defi ned a malaria case as an illness resulting in a positive result on a rapid diagnostic test or thin blood smear.We conducted the fi eld investigation in the capital during February 28-March 22, 2019. We obtained a dried blood spot on fi lter paper from each patient and stored the samples in a sealed plastic pouch until processing. We extracted DNA from the samples and