Resurgence and Seasonal Dynamics of Crimean-Congo Haemorrhagic Fever in Iraq: A Retrospective Analysis of the 2021 to 2024 Epidemic Wave

Abstract Objective Crimean-Congo haemorrhagic fever (CCHF) represents a critical zoonotic threat with expanding endemicity across the Middle East. Following decades of occurrence, Iraq experienced an unprecedented resurgence, Iraq experienced an unprecedented resurgence of CCHF between 2021 and 2024. We characterised the epidemiological dynamics, spatiotemporal patterns, and case fatality trends of this resurgence to inform targeted public health interventions. Methods and Design We conducted a retrospective analysis of laboratory-confirmed CCHF cases reported to the World Health Organization (WHO) Iraq office in Sulaymaniyah during June 2021- May 2024. Data on case demographics, geographic distribution, seasonal trends, and mortality outcomes were extracted from the national surveillance database. Descriptive epidemiological analyses were performed using SPSS v27.0, with temporal patterns visualised through heat mapping and weekly case distribution analyses. Case fatality rates (CER) were calculated as the proportion of deaths among confirmed cases per epidemiological week. Results A total of 1,089 laboratory-confirmed CCHF cases were identified over the 36-month surveillance period, with marked interannual variation. Following relatively limited transmission in 2021 (n=45), cases increased substantially in 2022 (n=250), culminating in an epidemic peak in 2023 (n=587 cases in July alone). Geographic analysis revealed a distinct latitudinal gradient, with southern governorates (Dhi Qar, Basra, Maysan) accounting for 79.2% (n=86/109) of 2023 cases, compared to minimal burden in northern regions (n=4; 3.7%). Seasonal analysis demonstrated consistent spring-summer amplification, with 78% of annual cases occurring between April and August. The overall CFR was 8.3% (range: 3.2 – 14.7%), with temporal clustering of fatal cases coinciding with epidemic peaks. A temporal decline was observed in early 2024, through persistent spring transmission (n=50, April-May 2024) indicates sustained enzootic circulation. Conclusion The 2021-2024 period represents the most significant CCHF epidemic wave in Iraq's surveillance history, characterised by southern geographic concentration and pronounced seasonality. These findings underscore the urgent need for vector control programs, livestock surveillance, and healthcare capacity strengthening in high-burden regions. Integration of CCHF surveillance with a One Health framework is essential to mitigate future epidemic potential in Iraq and the broader Middle East region.