Modelling Household, Behavioural, and Environmental Determinants of Lassa Virus Exposure Using Formative Risk Indices

Lassa fever remains a major public health threat in West Africa, yet the household and behavioural determinants of prior Lassa virus exposure are not sufficiently understood. This study examined environmental, behavioural, and demographic factors associated with Lassa virus IgG seropositivity among residents of selected states in North-Central Nigeria. Analysis was carried out on baseline data from 958 participants enrolled in the first phase of an ongoing longitudinal cohort study, which collected information on rodent exposure, house integrity, food safety practices, and household composition. Formative indices were constructed and standardised, and logistic regression models with 1000-iteration bootstrap estimation were used to identify predictors of IgG positivity. Seroprevalence of Lassa virus IgG was 19%, while IgM positivity was 1.15%. Rodent activity around and within homes was widespread, with more than 86% of participants reporting rodent presence. Logistic regression analysis showed that rodent exposure (standardised coefficient 0.20, 95% CI 0.02–0.43) and participant age (0.20, 95% CI 0.05–0.35) were significant predictors of IgG seropositivity. Household size demonstrated a strong inverse association (−0.41, 95% CI −0.68 to −0.20). House integrity and food safety formative indices exhibited weak and non-significant effects. Model performance was acceptable (AUC 0.63; Brier score 0.148), and variance inflation factor values confirmed negligible multicollinearity. These findings emphasised the continuing role of rodent exposure and demographic factors in Lassa virus transmission risk. This implies that there is a need to strengthen community-level rodent control and household-based prevention strategies, which can help to reduce exposure.