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.

[Study on potential risks of schistosomiasis transmission in Grand Canal West water diversion route of eastern route project of South-to-North Water Diversion Project].

OBJECTIVE: To understand the potential risks of Oncomelania hupensis diffusion and schistosomiasis transmission in the Grand Canal west water diversion route of the eastern route project of the South-to-North Water Diversion Project. METHODS: The engineering layout from Nanyun west floodgate to Hongze Lake, the aquaculture along Hongze Lake, and the data of hydrology and transferred water were investigated. The investigations on Oncomelania hupensis and schistosomiasis were carried out in the surveillance sites of Jinbao Channel and Hongze Lake. The possibilities of snail spreading and schistosomiasis transmission were researched. RESULTS: Oncomelania snails lacked their breeding environment and ecological condition in the Hongze Lake region. The engineering facilities of the Jinhu and Hongze pumping stations went against the snail spreading. The water levels at all steps decreased gradually from Hongze Lake to Jinbao Channel. Therefore, the pumping stations were necessary when the water transferred to Hongze Lake. The multi-year average diverted water volume reached 2.558 billion cubic meters a year in the Jinbao Channel. Of the total diverted water volume, there was 75% of the volume in drought years. The Oncomelania snails were not found in the surveillance sites of the Jinbao Channel and the Hongze Lake region from 2008 to 2011. A total of 3 088 residents were examined with the serology tests and the positive rate was 0.29% in 2008. Totally 4 758 overwater flow people were examined with the serology tests and the positive rate was 2.42% from 2008 to 2011. The serum positive rate was higher in the overwater flow people than that in the residents (chi2 = 0.083, P < 0.01). The stool examinations were all negative in the above mentioned serum positive people. CONCLUSIONS: The Hongze Lake area has still no Oncomelania snail breeding and schistosomiasis endemic so far. There are also no schistosomiasis re-prevalent signs in the Jinbao Channel area where schistosomiasis was once prevalent. The Oncomelania snail breeding and diffusion, and schistosomiasis endemic are unlikely to appear in the Grand Canal west water diversion route of the eastern route project of the South-to-North Water Diversion and Hongze Lake area.