Human babesiosis in Alsace

•Our study is the largest study of human babesiosis performed in Europe. It highlights that symptomatic infections are more common than expected, occurring primarily in immunocompetent individuals. It seems relevant to research babesiosis in patients presenting with febrile flu-like illness using blood smear and then PCR and/or several serological tests (seroconversion) in case of negative blood smear. Human babesiosis is a rare parasitic anthropozoonosis transmitted to humans by tick bites. Fifty-six cases of human babesiosis have been recorded in Europe. Two cases of babesiosis were reported in Alsace, France, in 2009. We performed a retrospective observational descriptive study to assess the epidemiology of the disease in Alsace. Patients were included if they had a positive serology result for Babesia and/or a positive blood smear and/or a positive PCR result. The tests were performed in the microbiology laboratories of the university hospitals of Strasbourg, the civil hospitals of Colmar, and the hospital of Mulhouse between January 1, 2005 and December 31, 2015. Included patients were divided into three groups: definite case group (positive PCR or positive blood smear or seroconversion), possible case group (positive serology results without seroconversion with a compatible clinical picture and without other confirmed diagnoses), and incompatible case group (positive serology results without seroconversion, without compatible clinical picture and/or with other confirmed diagnoses). The compatible clinical picture was defined by the presence of flu-like symptoms and fever (≥38°C). Fifty-one patients had at least one positive result. Three cases were excluded (missing files). There were six definite cases, 12 possible cases, and 30 incompatible cases. All patients in the definite case group were immunocompetent. No deaths occurred. Human babesiosis is probably underdiagnosed due to its non-specific symptoms, lack of awareness about the disease, and the difficulty in making a diagnosis. La babésiose humaine est une anthropozoonose parasitaire rare transmise à l’homme par piqûre de tique infectée. En Europe, on comptabilise 56 cas de babésiose humaine. En 2009, deux cas de babésiose ont été rapportés en Alsace (France). Nous avons réalisé une étude descriptive observationnelle rétrospective pour définir l’épidémiologie de la babésiose en Alsace. Les patients ont été inclus s’ils avaient une sérologie positive à B. divergens et/ou un frottis sanguin posit