Epidemiological characteristics and hospital outcomes of hospitalized Lassa fever cases during the 2022-2023 outbreak in Liberia

Abstract

Background Lassa fever is an endemic and immediately notifiable disease in Liberia, and one laboratory confirmed case constitutes an outbreak. We described the epidemiological characteristics and hospital outcome of Lassa fever cases hospitalized during the 2022-2023 outbreak in Liberia. Methods A cohort study was conducted using routine Lassa fever surveillance data from the 2022-2023 outbreak in Liberia. Descriptive statistics were used to summarize the data and log binomial regression to assess the association between epidemiological characteristics and mortality. Results A total of 439 suspected Lassa fever cases were reported. The median age was 22 (interquartile range: 10-33) years and 233 (53%) were women. The median number of days between symptom onset and admission was 4 (IQR 2-7). Of the 439 cases, 416 (95%) were tested for Lassa fever and 138 were confirmed with 33% positivity rate. The majority, 290 (69%), of confirmed cases were <30 years, 78 (57%) were females, and 81 (59%) were reported during the dry season (October – March). Contact with rodents, 94 (68%), was the commonest mode of exposure. Fever, 128 (93%), malaise, 121 (88%), headache, 114 (83%) and myalgia, 114 (83%) were the most common clinical characteristics. There were 83 (19%) deaths among hospitalized suspected Lassa fever cases - 42 deaths (15%) among 278 individuals who tested negative and 41 among confirmed cases with 30% case fatality rate (CFR). The highest CFR was recorded among those aged 40-49 years, 8 (67%) and those aged≥50, 5 (63%). There was no significant association between epidemiological characteristics and Lassa fever mortality. Conclusions The outbreak highlighted a high disease burden of Lassa fever with young adults disproportionately infected, and substantial mortality, even among those who tested negative for the virus. This underscores the urgent need for preventive measures like vaccines and health education campaigns.