Epidemiology of Lassa Fever in Kaduna State, Nigeria: Insights from the 2024 Outbreak

Introduction: Lassa fever outbreaks cause 10,000 deaths annually in West Africa. Nigeria has seen a steady rise in documented cases and deaths from Lassa fever since 2016. The largest outbreak in Nigeria was in 2018, with 1,893 cases and 106 deaths. LF is endemic in some Nigeria states. It occurs all year round with high number of cases seen occurring during the dry season between November to April. Primary infection occurs when Lassa virus-infected rodents come into contact and are exposed to their excreta, blood, or meat. Incubation takes 2 to 21 days. Symptoms are difficult to distinguish from malaria, typhoid, dengue, yellow fever, and other viral hemorrhagic fevers. Clinical manifestations range from asymptomatic to mild to severe fulminant disease. Ribavirin can improve outcomes. Overall mortality is between 1% and 15%. We reviewed the Lassa fever outbreak in Kaduna State, Nigeria, occurring between February and March 2024. Methods: We conducted a secondary data analysis of the surveillance data from the Kaduna state line list and laboratory confirmations during the outbreak period. We abstracted sociodemographic data recorded using the Surveillance Outbreak Response and Management System (SORMAS). Treatment with ribavirin, patient outcome (alive/dead), and laboratory results were also extracted. We managed the data using SPPS version 23.0. Results: Eighty-seven suspected cases were identified and investigated; with most within the ages of 20-29 years and mean age 32.5 ±17.6 years. There were 15 laboratory confirmed cases and 11 deaths (case fatality rate: 73.3%). Kaduna South LGA recorded the highest number of cases, accounting for 46.7% of the total. We observed no statistically significant association between occupation, sex, age, and mortality risk. However, certain age groups were disproportionately affected, with the highest burden of illness among in 20-29 years (CFR = 26.7%), as well as among females (67%), with 4 out of 11 deaths were healthcare workers (HCWs). The use of ribavirin treatment did not have a significant impact on mortality rates during this outbreak. Conclusion: The outbreak highlighted the persistent public health challenges posed by LF in Nigeria. Notably, (HCWs) emerged as a vulnerable population. There is a need to implement targeted interventions for the most affected age group, strengthen protective measures for HCWs. It is also important to improve surveillance in high-incidence LGAs, reassess ribavirin's efficacy, prioritizing community awareness among high reporting LGAs, and conduct research to understand the high CFR.