Crimean-Congo hemorrhagic fever in Türkiye, 2017-2024: evolving epidemiology and implications for surveillance

Crimean-Congo hemorrhagic fever (CCHF) is a severe tick-borne viral disease endemic in parts of Asia, Europe, and Africa. Türkiye reports the highest number of cases in the WHO European Region and maintains a comprehensive national surveillance system. This study aimed to characterize the demographic, temporal, and geographic patterns of CCHF and examine the influence of climatic and ecological factors on disease dynamics.

We analyzed national surveillance data from the Ministry of Health of Türkiye for 2017-2024, including all individuals diagnosed with CCHF (ICD-10 code A98.0). Data were obtained from Türkiye's national digital health infrastructure (e-Nabız), which integrates real-time reporting from all levels of the healthcare system-including primary care centers, secondary and tertiary hospitals, university hospitals, and private facilities-providing nationwide coverage of reported CCHF cases. The primary outcome was the annual number of CCHF cases identified through national surveillance. Secondary outcomes included mortality, demographic characteristics (age, sex, and province of residence), and temporal distribution by month and year of diagnosis. We also evaluated the performance of a previously validated forecasting model incorporating climatic, ecological, and livestock-related covariates.

A total of 7776 CCHF cases were reported between 2017 and 2024, with peak incidence observed in 2021. Men accounted for 63.8% of cases, the mean patient age was 45.3 years, and the overall case-fatality rate was 4.8%. Cases were concentrated in endemic regions of northeastern Central Anatolia, Eastern Anatolia, and the southern Black Sea region, with clear seasonal peaks during spring and summer. Forecasts from a previously validated model closely approximated observed annual case counts, including 931 predicted versus 918 observed cases in 2024, although larger derivations occurred during the COVID-19 pandemic period, specifically in 2021 (972 predicted vs 1314 observed cases).

Integrating ecological and contextual drivers into surveillance and forecasting frameworks can strengthen early warning capacity for CCHF. As tick habitats expand and the risk of CCHF emerges in parts of southern Europe, Türkiye's national surveillance experience provides valuable insights for anticipating and responding to evolving transmission dynamics.