Risk Factors for Bunyavirus-Associated Severe Fever with Thrombocytopenia Syndrome: A Community-Based Case-Control Study.

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by a novel bunyavirus. Previous studies about risk factors for SFTSV infection have yielded inconsistent results, and behavior factors have not been fully clarified. METHODS: A community-based, 1:4 matched case-control study was carried out to investigate the risk factors for SFTS in China. Cases of SFTS were defined as laboratory-confirmed cases that tested positive for real-time PCR (RT-PCR) for severe fever with thrombocytopenia syndrome bunyavirus (SFTSV) or positive for IgM antibodies against SFTSV. Controls of four neighborhood subjects were selected by matching for sex, age, and occupation. Standardized questionnaires were used to collect detailed information about their demographics and risk factors for SFTSV infection. RESULTS: A total of 334 subjects participated in the study including 69 cases and 265 controls. The median age of the cases was 59.5 years, 55.1% were male, and 87.0% were farmers. No differences in demographics were observed between cases and controls. In the final multivariate analysis, tick bites two weeks prior to disease onset (OR = 8.04, 95%CI 3.34-19.37) and the presence of weeds and shrubs around the house (OR = 3.46, 95%CI 0.96-12.46) were found to be risk factors for SFTSV infection; taking preventative measures during outdoor activities (OR = 0.12, 95%CI 0.01-1.01) provided greater protection from SFTSV infection. CONCLUSIONS: Our results further confirm that SFTSV is transmitted by tick bites and prove that preventative measures that reduce exposure to ticks can prevent SFTSV infection. More efforts should be directed toward health education and behavior change for high-risk populations, especially outdoor workers, in SFTS endemic areas.

A family cluster of infections by a newly recognized bunyavirus in eastern China, 2007: further evidence of person-to-person transmission.

BACKGROUND: Seven persons in one family living in eastern China developed fever and thrombocytopenia during May 2007, but the initial investigation failed to identify an infectious etiology. In December 2009, a novel bunyavirus (designated severe fever with thrombocytopenia syndrome bunyavirus [SFTSV]) was identified as the cause of illness in patients with similar clinical manifestations in China. We reexamined this family cluster for SFTSV infection. METHODS: We analyzed epidemiological and clinical data for the index patient and 6 secondary patients. We tested stored blood specimens from the 6 secondary patients using real time reverse transcription polymerase chain reaction (RT-PCR), viral culture, genetic sequencing, micro-neutralization assay (MNA), and indirect immunofluorescence assay (IFA). RESULTS: An 80-year-old woman with fever, leucopenia, and thrombocytopenia died on 27 April 2007. Between 3 and 7 May 2007, another 6 patients from her family were admitted to a local county hospital with fever and other similar symptoms. Serum specimens collected in 2007 from these 6 patients were positive for SFTS viral RNA through RT-PCR and for antibody to SFTSV through MNA and IFA. SFTSV was isolated from 1 preserved serum specimen. The only shared characteristic between secondary patients was personal contact with the index patient; none reported exposure to suspected animals or vectors. CONCLUSIONS: Clinical and laboratory evidence confirmed that the patients of fever and thrombocytopenia occurring in a family cluster in eastern China in 2007 were caused by a newly recognized bunyavirus, SFTSV. Epidemiological investigation strongly suggests that infection of secondary patients was transmitted to family members by personal contact.