Epidemiological and etiological investigation of a rare family cluster caused by severe fever with thrombocytopenia syndrome in Anhui Province in 2023.

Background: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease discovered in the 21st century. Human-to-human transmission of the disease has been documented, but the mechanisms of transmission require further investigation.

Methods: Epidemiological investigations and genetic analyses of the patients were conducted, and a retrospective cohort study was performed to analyze potential risk factors for person-to-person transmission.

Results: According to epidemiologic investigations, 14 secondary cases had a clear history of exposure to blood and body fluids, and 3 secondary cases may have been exposed to aerosols in a poorly ventilated environment. Risk factor assessment revealed that the risk of SFTS was 6.778 times higher [RR = 6.778, 95%CI = 1.570-29.354] among those who had direct blood contact with the indicated patient compared to those who did not, and exposure to bloody secretions from the corpse was associated with a 12.800 times higher risk for SFTS [RR = 12.800, 95%CI = 1.479-110.789] compared to contact with the blood, bloody fluids, or secretions of living patients.

Conclusions: Contact with the blood of a deceased individual during funeral rites was associated with secondary cases of SFTS. The cluster outbreak is suspected to be due to person-to-person transmission of SFTSV, likely through direct contact with the blood of an SFTS patient, while the spread of aerosols in enclosed environments is also an undeniable mode of transmission.