Aims Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease caused by the SFTS virus; primary manifestations are fever, thrombocytopenia, leukopenia and gastrointestinal symptoms. Before an aetiological diagnosis is made, SFTS patients can undergo bone marrow examination due to cytopenias. Although several studies have reported on bone marrow examination in SFTS patients, most do not provide adequate details. Bone marrow findings in SFTS patients were investigated in this study.

Methods An observational study was conducted in SFTS patients who were hospitalised between 2013 and 2014 in two university hospitals in South Korea. Patients were included in the study if SFTS was confirmed by real-time PCR for the SFTS virus and a bone marrow examination was conducted. The morphologic findings of the bone marrow samples were reviewed.

Results Three cases met the study inclusion criteria. One patient died of multiple organ failure. Haemophagocytosis was evident in the bone marrow samples of all three patients. Histiocytic hyperplasia and haemophagocytosis were more pronounced in the fatal case. One patient was diagnosed as having haemophagocytic lymphohistiocytosis.

Conclusions Haemophagocytosis in the bone marrow of SFTS patients may be common. In SFTS endemic areas, SFTS should be one of the differential diagnoses of fever of unknown origin with haemophagocytosis in the bone marrow.