Co-Endemic Zoonoses, Divergent Dynamics: A Comparative Spatiotemporal Analysis of Crimean-Congo Hemorrhagic Fever and Brucellosis with Implications for Integrated Surveillance.

Abstract

Co-endemic zoonoses may occur in the same broad geographic settings but not necessarily the same communities or time periods. This study investigated whether Crimean-Congo hemorrhagic fever (CCHF) and brucellosis exhibit convergent or divergent spatiotemporal patterns across geographic scales in a livestock-dependent, CCHF-endemic province of Türkiye. This retrospective study analyzed confirmed human CCHF and brucellosis cases reported to the national infectious disease surveillance system between 2011 and 2024. Temporal analyses, kernel density estimation, settlement-level random labeling, and within- and cross-disease Knox tests were performed. Among the 611 eligible cases, CCHF (n = 442; 72.3%) and brucellosis (n = 116; 19.0%) accounted for 91.3%. CCHF was strongly seasonal, with 99.3% of cases occurring between April and September, whereas brucellosis occurred throughout the year. Although broad density surfaces partially overlapped, same-settlement co-occurrence was substantially lower than expected (O/E = 0.37; p < 0.001) and remained so in the sensitivity analysis (O/E = 0.74; p = 0.001). Cross-disease analysis showed no evidence that CCHF and brucellosis occurred closer together in both space and time than expected. Annualized CCHF concentration peaked in 2020-2021, whereas brucellosis peaked in 2022-2024. Integrated surveillance may use shared regional infrastructure, but interventions should be tailored to disease-specific settlements, transmission pathways, and periods of risk.