Retrospective Multicenter Study of Human Granulocytic Anaplasmosis, France, 2012-2024

Human granulocytic anaplasmosis (HGA), caused by Anaplasma phagocytophilum transmitted through tick bites, remains poorly documented in France. We conducted a retrospective, multicenter study of cases in Alsace during 2012-2024, including 39 HGA episodes in 38 patients PCR positive for A. phagocytophilum. Most (63.2%) patients were men, median age was 60.5 years, and 76.3% lived in rural areas. A tick bite was reported in 61.6% of cases. Frequent symptoms included fever (97.4%), fatigue (61.5%), and headache (61.5%). Laboratory findings showed elevated C-reactive protein (100%), thrombocytopenia (94.9%), leukopenia (59.0%), and cytolysis (66.7%). One patient had secondary hemophagocytic lymphohistiocytosis. Most (87.2%) patients were hospitalized; none required intensive care unit admission. Doxycycline was administered in 29 cases, and all patients recovered. HGA should be considered in febrile patients with recent tick exposure and cytopenia. Although often benign, rare severe HGA forms can occur and justify increased clinical awareness, especially in A. phagocytophilum-endemic areas.