Seroprevalence and risk factors for Crimean-Congo hemorrhagic fever virus exposure among febrile patients in northern Tanzania.

Background: Crimean-Congo hemorrhagic fever is a tick-borne zoonotic disease that may be severe and is present in many African countries. We aimed to understand the seroprevalence and risk for Crimean-Congo hemorrhagic fever virus in Tanzania by testing archived serum samples from patients enrolled in a prospective cohort study.

Methods: We prospectively enrolled febrile inpatients and outpatients from 2012 through 2014 at two referral hospitals in northern Tanzania. Archived serum samples were tested for Crimean-Congo hemorrhagic fever virus antibodies initially by a Luminex assay screen followed by confirmation with immunofluorescence assay. Evidence of exposure to Crimean-Congo hemorrhagic fever virus was defined as antibody detection by Luminex and confirmed by immunofluorescence assay. Questionnaire data were used to construct logistic regression models to understand factors associated with prior exposure to Crimean-Congo hemorrhagic fever virus. Domains of predictor variables included sociodemographics, livestock-rearing activities, and environmental factors.

Results: Of 735 participants included, antibodies to Crimean-Congo hemorrhagic fever virus nucleocapsid protein were detected by Luminex assay in 23 (3.1%) and confirmed by immunofluorescence assay in 13 (1.8%). In multivariable logistic regression, prior exposure to Crimean-Congo hemorrhagic fever virus was associated with self-report of milking livestock in the past month (adjusted OR [aOR]: 12.6, 95% CI 1.6-99.8) and natural log increase in goat density (head/km²; aOR: 1.7, 95% CI: 1.1-2.7).

Conclusions: We show serologic evidence of prior exposure to Crimean-Congo hemorrhagic fever virus among humans in northern Tanzania. Similar to other settings, our results suggest that exposure is closely linked to livestock activities. Additional research is warranted to understand reservoirs and modes of transmission of Crimean-Congo hemorrhagic fever virus to humans in northern Tanzania.