Incidence of human granulocytic anaplasmosis in returning travellers with fever

Background Although tick-borne pathogens have been reported as an important cause of imported fever, the incidence of Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis (HGA), in travellers is unknown. Methods We conducted a prospective cohort study to investigate the aetiologies of fever in returning travellers (November 2017—July 2019). Polymerase chain reaction for msp2 gene amplification and indirect immunofluorescence assay for A. phagocitophilum were performed in all returning travellers with undifferentiated non-malarial fever. Results Among 141 travellers included, 8 patients were diagnosed with probable or confirmed HGA. The overall incidence rate of HGA was 19.9 cases/1000 person—week of travel. The main destination of travel was Asia, accounting for 62.5% patients with HGA. Co-infections were found in 37.5% of patients with HGA. Conclusions Diagnosis of HGA and empirical treatment with doxycycline should be considered in travellers with fever.