Lassa fever epidemiology and predictors of mortality in Ebonyi State, Nigeria - A five-year retrospective analysis from 2019 to 2023

Lassa fever (LF) is a viral disease that is widespread throughout West Africa, with significant global health consequences. Nigeria bears the highest burden (1309 confirmed cases in 2024) of LF among all endemic countries. Within Nigeria, Ebonyi State bears a high burden of cases. Clinical observations suggest that there may be an increase in the geographic spread and case fatality rate of LF across the State. Ebonyi State case-based data on confirmed cases from 2019 to 2023 collated on the Nigeria Centre for Disease Control and Prevention (NCDC) Surveillance, Outbreak Response Management and Analysis System (SORMAS) platform were analyzed. Descriptive statistics, spatial distribution and time series analysis were performed. Multivariate logistic regression analysis was used to identify predictors of LF mortality and factors associated with PCR positivity. A total of 1,624 suspected cases were reported, 1,343 and 273 were laboratory negative and positive respectively, while 8 probable cases were reported. The yearly number of cases remained stable throughout the study period. Out of the 273 confirmed, 107 died from LF, resulting in a case fatality rate (CFR) of 39.2%. CFR increased non-significantly over time, ranging from 28.6% to 55.8%. Variations in geographic distribution were observed; in 2019 ten local government areas (LGAs) were affected compared to twelve in 2020. A higher incidence was observed between January and March annually. Age above 44 years, bleeding and seizures were significant predictors of mortality. Lower incidence of cases was consistently reported in the Southern LGAs. PCR positivity was associated with individuals who reside in Ebonyi LGA and who have had contact with confirmed cases. The increase in CFR and identification of high-burden areas will help shape policies, allocate resources and provide actionable intervention strategies to combat LF in the State.