BACKGROUND:
In January 2025, Edo State, Nigeria, exceeded its epidemic threshold for Lassa fever, reporting 76 confirmed cases across hotspot local government areas (LGAs) including Etsako West, Esan West, and Esan North-East. Despite recurrent outbreaks, evidence on individual-level risk factors remains limited. We investigated to describe the epidemiology of the outbreak and identify risk factors for infection.

METHODS:
We conducted a 1:3 unmatched case-control study. A case was defined as an RT-PCR-positive Lassa fever patient residing in Edo State during January 2025. Controls were residents of the same locality without Lassa fever infection. We collected data using structured questionnaires covering sociodemographic, environmental, and behavioural exposures. Logistic regression was performed to determine associations between exposures and infection.

RESULTS:
A total of 28 cases and 84 controls were enrolled. The mean age was 32.5 years (SD ±15.0), with no significant age or gender differences between groups. A single case of Lassa fever was detected among healthcare worker and the overall case fatality rate was 14.5%. Contact with a sick person within 21 days prior to illness onset was strongly associated with Lassa fever infection (adjusted OR = 23.2; 95% CI: 6.4–83.9). Other exposures—including rodent presence, improper food storage, poor hand hygiene, and water source—did not show statistically significant associations.

CONCLUSIONS:
Close contact with infected individuals was the primary risk factor for Lassa fever transmission in Edo State during this outbreak. The low case rate among healthcare workers and moderate case fatality rate suggests improvements in infection prevention and control practices. Strengthening contact tracing, public education, and targeted interventions in endemic LGAs remain critical for outbreak response.