ABO Blood Groups and Clinical Outcomes in Crimean-Congo Hemorrhagic Fever: Insights From a Large Turkish Cohort.

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne viral disease in which host-related factors contributing to disease susceptibility and clinical outcomes remain incompletely understood. We aimed to evaluate the impact of ABO and Rh blood groups on susceptibility and prognosis in patients with CCHF and to investigate their relationship with epidemiological characteristics in a large real-world cohort. This retrospective study included 1143 adult patients with PCR-confirmed CCHF who were followed at our center between April 2015 and September 2024. ABO and Rh blood groups were determined using the Hitachi ElecSys 2010 Rack system, and hematological, biochemical, and coagulation parameters were evaluated simultaneously with CCHF PCR testing at hospital admission. Clinical outcomes, viral load, epidemiological characteristics, disease severity according to the Severity Grading Score (SGS), and laboratory findings were compared among blood groups. In addition, multivariable logistic regression analysis was performed to identify independent predictors of in-hospital mortality. Of the 1143 patients, 732 (64.0%) were male and 411 (36.0%) were female; 548 patients had blood group A, 353 group O, 154 group B, and 88 group AB. Overall in-hospital mortality was 8.5% (97/1143). No significant differences were observed among ABO or Rh blood groups regarding in-hospital mortality, intensive care unit (ICU) requirement, viral load, or reported tick exposure. Although no deaths or ICU admissions occurred in the AB Rh-negative subgroup, this subgroup comprised only 13 patients. Significant differences were identified only in amylase and lipase levels among blood groups, whereas SGS, ferritin, interleukin-6, and other laboratory parameters were comparable. In the multivariate analysis, ABO and Rh blood groups were also not independently associated with in-hospital mortality. These findings suggest that ABO and Rh blood groups are not associated with clinically meaningful differences in disease severity or prognosis in patients with CCHF. Further multicenter prospective studies are warranted to validate these findings.