Detection of SFTS virus RNA and antibodies in severe fever with thrombocytopenia syndrome surveillance cases in endemic areas of China

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is a newly identified severe infectious disease caused by SFTS phlebovirus (SFTSV). SFTS monitoring has been carried out since 2010 in mainland China. We analysed the detection results of SFTSV RNA and antibody in SFTS surveillance cases to provide basic data for SFTS diagnosis. METHODS: This study was conducted in Shandong Province. Sera of SFTS surveillance cases were collected to detect SFTSV RNA and antibody by real-time RT-PCR and enzyme-linked immunosorbent assay, respectively. Detection rates were calculated. SPSS 18.0 (Chicago, IL, USA) was used for statistical analysis to compare the detection rates of SFTSV RNA and antibodies among different sera groups. RESULTS: A total of 374 SFTS surveillance cases were enrolled. Overall, 93.3% (349/374) of the sera samples were collected within 2 weeks after onset, and 6.7% (25/374) were collected between 15 days and 45 days. Of these, 183 (48.9%) were positive for SFTSV RNA. The SFTSV RNA-positive rate peaked (52.2%) in samples collected ≤7 days after onset and then showed a decreasing trend. The detection rate of SFTSV-specific IgM antibody was 30.5% (46/151) and was highest in samples collected between 8 and 14 days (43.3%, 26/60). The positive rate of SFTSV-specific IgG antibody (17.9%, 27/151) showed an increasing trend with the specimen collection time. In total, 74.8% (113/151) of sera samples had the same SFTSV RNA and IgM antibody detection results. However, 23.2% (29/125) of SFTSV RNA-negative cases were IgM antibody-positive, and 8.6% (9/105) of IgM antibody-negative cases were SFTSV RNA-positive. CONCLUSIONS: SFTSV RNA detection was preferred for SFTSV infection during disease surveillance. For highly suspected SFTS cases, IgM antibody is suggested to make a comprehensive judgement.