Clinical and Epidemiologic Findings from Enhanced Monkeypox Surveillance in Tshuapa Province, Democratic Republic of the Congo During 2011–2015

Background: Monkeypox is an emerging zoonosis endemic to Central and Western Africa. Increasing incidence and travel-associated cases worldwide call for renewed efforts to understand its epidemiologic and clinical characteristics.Methods: We analyzed case investigation forms obtained from enhanced surveillance in Tshuapa Province, Democratic Republic of the Congo, during 2011–2015. Infections were confirmed by real-time PCR. We evaluated differences in cumulative incidence, exposure histories, and clinical presentation of confirmed cases by sex and age group.Findings: 1,057 laboratory confirmed cases were reported. Average annual incidence was 14·1 per 100,000 (95% CI: 13·3–15·0), more than twice that reported in the 1980s. Incidence was higher in males (incidence rate ratio: 1·21, 95% CI 1·07–1·37), except among persons aged 20–29 years (incidence rate ratio males: females: 0·70, 95% CI: 0·51–0·95). Females with monkeypox aged 20–29 years also reported a high frequency of exposures (26·2%) to people with monkeypox-like symptoms. The age group with highest incidence was among 10–19-year-old males, a cohort that accounted for the highest proportion of animal exposures (37·5%). Incidence was significantly lower among those presumed to have received smallpox vaccination versus those presumed unvaccinated. No differences were observed by age group in lesion count by body site, median lesion count, or lesion severity score.Interpretation: Our study reveals potential waning immunity to monkeypox given discontinuation of smallpox vaccination and an increasing proportion of cases attributed to human exposures. Cases were widely distributed across age and sex and suggest frequent exposures that follow socio-cultural norms.Funding Statement: This study was funded by the U.S. Centers for Disease Control and Prevention.Declaration of Interests: None to declare.Ethics Approval Statement: Surveillance was conducted in accordance with Congolese national guidelines. The activity was determined non-research by a CDC human subjects advisor.