Age Is a Critical Risk Factor for Severe Fever with Thrombocytopenia Syndrome

Abstract

BackgroundSevere Fever with Thrombocytopenia Syndrome (SFTS) is an emerging infectious disease in East Asia. SFTS is a tick borne hemorrhagic fever caused by SFTSV, a new bunyavirus named after the syndrome. We investigated the epidemiology of SFTS in Laizhou County, Shandong Province, China.MethodsWe collected serum specimens of all patients who were clinically diagnosed as suspected SFTS cases in 2010 and 2011 in Laizhou County. The patients' serum specimens were tested for SFTSV by real time fluorescence quantitative PCR (RT-qPCR). We collected 1,060 serum specimens from healthy human volunteers by random sampling in Laizhou County in 2011. Healthy persons' serum specimens were tested for specific SFTSV IgG antibody by ELISA.Results71 SFTS cases were diagnosed in Laizhou County in 2010 and 2011, which resulted in the incidence rate of 4.1/100,000 annually. The patients ranged from 15 years old to 87 years old and the median age of the patients were 59 years old. The incidence rate of SFTS was significantly higher in patients over 40 years old and fatal cases only occurred in patients over 50 years old. 3.3% (35/1,060) of healthy people were positive to SFTSV IgG antibody. The SFTSV antibody positive rate was not significantly different among people at different age groups.ConclusionOur results revealed that seroprevalence of SFTSV in healthy people in Laizhou County was not significantly different among age groups, but SFTS patients were mainly elderly people, suggesting that age is the critical risk factor or determinant for SFTS morbidity and mortality.

Presence of Antibodies against Severe Fever with Thrombocytopenia Syndrome Virus in Non-Endemic Areas of China

“…Furthermore, we found that the rate of SFTSV-IgG seropositivity was consistent among male and female tea pluckers, but was much higher among men than women for all participants. Ding et al showed that age is a critical risk factor for SFTS morbidity and mortality (17). In our study, we found that age is also a risk factor for SFTSV infection.…”

“…We used an enzyme-linked immunosorbent assay kit obtained from the National Institute for Viral Disease Control and Prevention and followed its instructions to test for SFTSV-specific immunoglobulin G (IgG) antibodies in sera samples (17,18). A sample of 100μl (1μl sera diluted in 100μl total sample) was added to each well and incubated at 37°C for 40 min.…”

Neutralizing antibodies to Severe Fever with Thrombocytopenia Syndrome Virus in general population, Shandong Province, China

“…These results suggested that age and occupation were potential risk factors of SFTSV infection in general population of Penglai County. The positive rate in this study was similar to the reported percentage (3.3%) recorded in Shandong Province 14 . However, it was much higher than that reported in Jiangsu (0.44%), lower than that in Shanxi (4.7%) 15,16 .…”

Severe fever with thrombocytopenia syndrome and its pathogen SFTSV

“…Recently SFTSV RNA has been detected from rodents and Asian house shrews in China [44].These data demonstrated that the domesticated animals, rodents and shrews have been widely infected by SFTSV in the endemic areas and they may act as amplifying hosts of SFTSV and play a major role in SFTSV transmitting. Approximately 1%e3% rural population in endemic area in China was infected with SFTSV [37e39, 45]. The SFTSV antibody positive rate was not significantly different among people at different age groups, but hospitalized SFTS patients were mainly middle and old aged populations and death mainly occurred in people old than 50 years old, suggesting age is a critical risk factor for severe disease and death of SFTS [45].…”

“…Approximately 1%e3% rural population in endemic area in China was infected with SFTSV [37e39, 45]. The SFTSV antibody positive rate was not significantly different among people at different age groups, but hospitalized SFTS patients were mainly middle and old aged populations and death mainly occurred in people old than 50 years old, suggesting age is a critical risk factor for severe disease and death of SFTS [45]. Clusters of SFTS cases have been reported in several provinces in China [1,46e50], suggesting a human-to-human transmission model of the disease.…”