Dengue fever outbreak in Mogadishu, Somalia 2011: Co-circulation of three dengue virus serotypes

Abstract

Background: In June 2011 an acute febrile illness (AFI) outbreak, with three deaths, was reported among African Union Mission in Somalia (AMISOM) peacekeepers in Mogadishu. All were negative for malaria by blood smear. An initial set of samples (n = 122) were sent to CDC-Kenya/Kenyan Medical Research Institute (CDC/KEMRI) laboratories to test for various viral hemorrhagic fevers by RT-PCR. A majority (82%) were positive for dengue virus (DENV). Methods & Materials: CDC-Kenya and CDC-Uganda subsequently supported AMISOM to implement an enhanced hospitalbased dengue fever surveillance system in two military hospitals in Mogadishu. Case defiantion: all patients with axillary temperature > 380C Results: During June-August 2011,134 (94%) of 143 blood samples from AFI cases were tested by RT-PCR and MAC-ELISA. Of these, 62% were positive for DENV by RT-PCR, 18% (n = 24) had a positive sole anti-DENV MAC-ELISA and 20% had a negative RT-PCR and MAC-ELISA. All specimens had negative malaria smear or RDT. Infections of DENV-1, DENV-2, DENV-3 and co-infections of DENV- 1/2 and DENV-2/3 sero-types were identified in 37%, 7%, 25%, 1%and 25%, respectively. Of the confirmed cases (n = 107; 75%), median age was 32 years (range 20-49), majority (96%) were male and 60% were hospitalized (median length of stay = 3.5 days). Of the hospitalized patients, 87% had leucopenia (WBC< 3.5x103 cells) and 83% thrombocytopenic (platelet count < 100x103 cells). Except for a high proportion of hemorrhagic manifestations (n = 14, 13%), frequency of other clinical findings (fever, headache, joint pains, vomiting and body pains) (>60%) was consistent as with other settings. Conclusion: Co-circulation of multiple dengue sero-types and possible repeated secondary heterotypic dengue infections may be responsible for a high proportion of severe forms of dengue, including death. The extent of severe dengue infection, co-circulation of three dengue serotypes and co-infection with multiple dengue sero-types has not been previously documented in African. Despite the limited scope of this study given the hospital-based design it appears the intensity of dengue fever transmission, severity of dengue in this setting appears under-reported especially in the civilian population. Given the frequent rotations of peacekeepers from Somalia, the potential of dengue viruses' importation to many African countries where the vectors exist is real.