Increasing trend of Lassa fever outbreak in Nigeria: The more you look, the more you see

Abstract

Background: Lassa fever (LF) is an acute viral hemorrhagic fever endemic in Nigeria. The bane of endemicity of LF has reached an unprecedented proportion in recent years; with each yearly outbreak bigger in cases, deaths and spread, compared to the previous years. A critical review of the increase and associated factors are presented in this paper. Methods and materials: This study is based on desk review, analysis of secondary data, review of surveillance indicators and Key Informant Interviews (KII) with members of the National Lassa Fever Technical Working Group at the Nigeria Centre for Disease Control. Case definition for suspected and confirmed cases of Lassa fever were interpreted as contained in the National IDSR Guideline. Prevalence, Case Fatality Rate (CFR) and Timeliness of report were computed and compared across the three years. Results: The study observed that reliable Lassa fever data was unavailable at the national level before 2017. However, in 2017, 1022 suspected cases were identified in 19 states and 322 tested positive for Lassa fever. Between 2017 and 2018, states have received training and tools on Lassa fever surveillance, state surveillance and response structure had been standardized and preparedness assessment were carried out. Case detection started early in 2018 and by December, 3498 suspects were identified representing about three-fold increase over previous year, and 633 cases tested positive. With further strengthening of the surveillance system in 2019, a total of 4099 suspected cases were identified with 739 confirmed for weeks 1–41, 2019. Similarly, deaths among cases increased from 127 (39.4% CFR) to 171 (27% CFR) to 154 (20.8% CFR) over the same time period. Conclusion: The period between 2016 and 2019 signify the improvement of the surveillance system for infectious diseases in Nigeria. The result can be translated to mean increase in number of cases of Lassa fever detection. The percent increase from 2018 to 2019 is 17% and this would continue to reduce until we reach an equilibrium. Only until this happens can we speculate on the burden of LF or we can also conduct a sero-prevalence study to determine the true burden of the infectious disease.