Low case fatality during 2017 cholera outbreak in Borno State, North Eastern Nigeria

Background: Cholera is endemic in sub-Saharan Africa, especially in areas affected by natural disaster and human conflict. Northeastern Nigeria is experiencing a health crisis due to the destruction of essential amenities such as health infrastructure, sanitation facilities, water supplies, and human resources by Boko Haram insurgents. In 2017, a cholera outbreak occurred in five local government areas (LGAs) hosting internally displaced persons. The Nigeria Center for Disease Control, World Health Organization, Mdecins Sans Frontires International, and several other organizations supported disease containment. An emergency operating center (EOC) established by the State Ministry of Health (SMoH) then coordinated the outbreak response. Methods: We conducted a retrospective analysis of data extracted from the line list utilized by the SMoH to investigate outbreaks. We evaluated the outbreak by time, place, and person. Attack rate by LGA and age-specific case fatality rate (CFR) was calculated based on cases with complete records for age, sex, place of residence, date of symptom onset, and disease outcome. Results: A total of 5889 cholera cases were reported from five LGAs with an overall attack rate of 395.3/100,000 population. Among 4956 cases with documented outcome, the overall CFR was 0.87%, with CFR ranging from 0% to 6.98% by LGA. The age-specific CFR was highest among those aged ≥60 years (1.92%) and least among those aged 20-29 years at 0.3%. The epidemiological curve revealed two peaks that coincided with periods of heavy rain and flooding. Conclusion: This study reports on the largest ever documented cholera outbreak in five LGAs in Borno State. The outbreak was focused in LGA hit hardest by the destructive activities of insurgents and then spread to neighboring LGAs. The low CFR recorded in this cholera outbreak was achieved through timely detection, reporting, and response by the coordinated efforts of the EOC established by the SMoH that harmonized the outbreak response.