Exploring the drivers of Crimean-Congo hemorrhagic fever in Southern Iraq

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Objectives Crimean-Congo Haemorrhagic Fever (CCHF) is a zoonotic viral tick-borne disease, which has seen a resurgence in Iraq in recent years, and this study aimed to explore environmental and socioeconomic drivers of this resurgence in southeastern Iraq. Methods We used weekly CCHF case data by province and demographic strata (sex, children, adults, older adults) and performed initial covariate exploration using Pearson correlation and penalised feature screening (LASSO, Elastic Net). We fitted generalised additive mixed models (GAMs; negative binomial) with cyclic seasonality and region‑level random effects to a subset of the best performing covariates. Residual temporal autocorrelation was assessed and AR(1) mixed‑effects refits were attempted until a best-fit model was identified. Results As anticipated, land-use and many socioeconomic covariates showed strong correlations in initial covariate exploration, and similar patterns were observed among humidity, temperature and precipitation. The main model (total cases) explained ~80% deviance, showing strong seasonality and spatial heterogeneity. The self‑calibrated Palmer Drought Severity Index and counts of incoming internally displaced persons were the most stable predictors. Conclusions In southeastern Iraq, CCHF risk was seasonal and spatially heterogeneous and environmental and socioeconomic contexts likely modulate outbreaks and resurgence.