Conference abstract

Risk factors for yellow fever transmission during an outbreak in Masaka, Rukungiri and Kalangala, Uganda, April 2016

Pan African Medical Journal - Conference Proceedings. 2017:6(10).20 Dec 2017.
doi: 10.11604/pamj-cp.2017.6.10.492

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Keywords: Yellow fever, aedes mosquitoes, disease outbreaks, forest

Risk factors for yellow fever transmission during an outbreak in Masaka, Rukungiri and Kalangala, Uganda, April 2016

Leocadia Kwagonza1,&, Ben Masiira1, Daniel Kadobera1, Alex Riolexus Ario1, Bao-Ping Zhu2

1Uganda Public Health Fellowship Program, Kampala, Uganda, 2US Centres for Disease Control and Prevention, Kampala, Uganda

&Corresponding author
Leocadia Kwagonza, Uganda Public Health Fellowship Program, Kampala, Uganda


Introduction: on March 28, 2016 a cluster of deaths resulting from jaundice and hemorrhagic symptoms occurred in Masaka, Central Uganda. We investigated this outbreak to determine the nature of disease, identify risk factors, and recommend control and prevention measures.

Methods: we defined a suspected case person as an onset in the residents of Masaka, Rukungiri and Kalangala districts from January 2016 onwards of fever not responding to malaria treatment, plus ≥2 of the following: Abdominal pain/diarrhea, headache, jaundice, unexplained bleeding. A confirmed case was a suspected case with positive IgM or PCR tests for yellow fever. We conducted medical records, reviews and active community case findings. In a case control study we compared potential exposures between 32 case persons and 128 asymptomatic controls matched by age, sex and village. We also conducted entomological studies and environmental assessments.

Results: we identified 32 cases (7 confirmed). The overall attack rate (AR, per 100,000) was 0.48 overall (6.4 Masaka, 3.1 Rukungiri and 1.9 Kalangala); the case fatality rate was 22% (7/32). Men (AR = 1.2/10,000) and persons aged 30-39 years (AR = 4.0/10,000) were most affected. 20 (63%) of 32 case persons and 35 (27%) of 128 control persons cultivated in forest areas (ORM-H = 4.3; 95% CI = 1.9 - 9.7); 23 (71%) of 32 case persons and 32 (25%) 128 control persons cultivate in swampy areas (ORM-H = 7.5; 95% CI = 2.0 -18). No one interviewed during this investigation was vaccinated against yellow fever. Sylvatic monkeys and Aedes mosquitoes were identified in the nearby forest areas.

Conclusion: this was a sylvatic yellow fever outbreak that occurred in a susceptible population, likely transmitted by mosquito bites during cultivation in forest and swampy areas. We recommended yellow fever vaccination in affected districts and enhanced yellow fever surveillance in neighboring districts. The outbreak stopped following the vaccination.