Characteristics of Lassa Fever Outbreak in Ondo State, Nigeria, Year 2019

Abstract

Background: Lassa fever (LF) is an acute viral haemorrhagic illness of a 2–21-day incubation period that occurs in West Africa. It is endemic in Nigeria and peaks during the first 12 weeks of the year. On January 22, 2019, the Nigeria Centre for Disease Control (NCDC) declared an outbreak of LF following an upsurge of LF cases in the country. A total of 213 confirmed cases including 41 deaths were reported from sixteen states including Ondo State. A multi-sectoral national rapid-response-team (RRT) was deployed to Ondo State to characterise the outbreak, assess its determinants, and institute control measures. Methods: An Emergency Operations Center (EOC) was activated to coordinate activities. We defined a suspected case as anyone with one or more of the following symptoms: malaise, fever, headache, sore throat, cough, vomiting and either history of contact with rodents, or a probable or confirmed LF case in the past 21 days, or any person with inexplicable bleeding between January 1, 2019, to February 26, 2019, in Ondo State. A confirmed case was any suspected case with laboratory confirmation. We conducted active case search, collected data using the LF case investigation form and reviewed the existing line list. We conducted contact tracing in hospitals and affected Local Government Areas (LGA). Data was analysed using and Epi info 7.0. Results: We identified 287 LF suspected cases in 6 LGAs; 118 were confirmed with 21 deaths (case fatality rate: 17.8%). The mean age was 39.2 ±20 years with a male-to-female ratio of 1.3:1. Of the 1,269 contacts line-listed, 20 became symptomatic, while 14 (70.0%) were confirmed positive. The secondary attack rate was 1.1%. Conclusion: The confirmed cases were more of primary cases, hence the need to focus more on reducing rodent-to-human transmission of LF. We recommend continuous education on community and health facility infection prevention control, contact tracing and enforcement of environmental sanitation measures across the state to mitigate future outbreaks