Investigation of Lassa Fever outbreak in Grand Bassa County, Liberia, 2021

Introduction: Lassa fever is an African viral haemorrhagic infection spread by contaminated rodent urine or feces. Every year, Lassa fever kills 5,000 individuals in West Africa. Three counties are known in Liberia to have Lassa fever. Cases are growing in previously disease-free areas, with a 56% fatality rate. Lassa fever was detected by a private health facility and reported to the Grand Bassa County Health Team through the district team on March 6, 2021. The County Surveillance Office organized a joint (District, County, and a resident of the Ghana Field Epidemiology and Laboratory Training Program (GFELTP)) rapid response team to investigate with aimed to confirm the outbreak, describe its magnitude and implement control and preventive measures. Methods: The investigation covered March to June 2021 in Grand Bassa County District. Stakeholders were consulted. Patients were interviewed, and their records checked. The standardized Lassa fever case definition was used to identify cases. Data was collected using the case investigation forms electronically by Kobo Collect and filling hard copy investigation forms. Data collected from cases were demographic data, date of onset of illness, signs and symptoms, travel history and exposure to animals or infected persons. A case search in the community and contact tracing revealed more cases. Cases were listed, and demographic and clinical data collected and summarized using proportions and frequencies. The communities were analyzed for environmental risk factors and blood samples were collected for Real-Time Polymerase Chain Reaction Testing (RT-PCR). Results: The index case was a 38-year-old female who was a resident of MIE Field camp located in Compound #3)with symptoms onset on the 1 March, 2021. She had a persistent high fever which did not resolve with anti-malarial and antibiotics. Three additional confirmed cases were detected through community case search. The district attack rate was 0.008 per 100,000, and the case fatality rate was 25% (1/4). The cases ages ranged from 24 to 55 years with a mean age of 45.5. Two (50%) were females. Overgrown weeds were seen close to residential areas, and the environmental hygiene was poor. Conclusion: An outbreak of Lassa fever in Grand Bassa County affected four residents in District #3, killing one. Community leaders were engaged and an organized cleanup exercises was conducted. Timely risk communication, rodent control, and environmental management helped control the outbreak. Healthcare workers should be periodically trained on the early detection of infectious diseases such as Lassa fever.