Epidemiologic Features and Environmental Risk Factors of Severe Fever with Thrombocytopenia Syndrome, Xinyang, China

Abstract

BackgroundSevere fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease discovered in rural areas of Central China in 2009, caused by a novel bunyavirus, SFTS virus (SFTSV). The disease usually presents as fever, thrombocytopenia, and leukocytopenia, with case-fatality rates ranging from 2.5% to 30%. Haemaphysalis longicornis was suspected to be the most likely vector of SFTSV. By the end of 2012, the disease had expanded to 13 provinces of China. SFTS patients have been reported in Japan and South Korea, and a disease similar to SFTS has been reported in the United States.Methodology/Principal FindingsWe characterized the epidemiologic features of 504 confirmed SFTS cases in Xinyang Region, the most severely SFTS-afflicted region in China from 2011 to 2012, and assessed the environmental risk factors. All cases occurred during March to November, with the epidemic peaking from May to July. The patients' ages ranged from 7 to 87 years (median 61 years), and the annual incidence increased with age (χ2 test for trend, P<0.001). The female-to-male ratio of cases was 1.58, and 97.0% of the cases were farmers who resided in the southern and western parts of the region. The Poisson regression analysis revealed that the spatial variations of SFTS incidence were significantly associated with the shrub, forest, and rain-fed cropland areas.ConclusionsThe distribution of SFTS showed highly significant temporal and spatial heterogeneity in Xinyang Region, with the majority of SFTS cases being elderly farmers who resided in the southern and western parts of the region, mostly acquiring infection between May and July when H. longicornis is highly active. The shrub, rain-fed, and rain-fed cropland areas were associated with high risk for this disease.

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

“…SFTS cases are mainly distributed among farmers living in mountainous or hilly rural areas (19). So far, more than two-thirds of the provinces in mainland China have reported cases of SFTS.…”

Spatial Analysis of Severe Fever with Thrombocytopenia Syndrome Virus in China Using a Geographically Weighted Logistic Regression Model

“…One such study used a Poisson regression analysis to show that the spatial variations in the incidence of SFTS were significantly associated with shrub, forest and rain-fed cropland areas in the Xinyang region of the Henan province in China [18]. Another study conducted spatial scan statistics and multivariate model of SFTS in China using the surveillance data from 2010 to 2013, and they detected three hot spots of SFTS in China and identified independent risk factors of the distribution of SFTS [50].…”

“…Moreover, many studies showed that tick-borne diseases like Lyme disease, rickettsiosis and tick-borne encephalitis have a strong association with environmental factors [25,26,27]. Considering that the majority of patients of confirmed SFTS cases lived in rural areas and were employed in agriculture [8,18], we hypothesize SFTS might be influenced by environmental factors and anthropogenic factors. Our study has two major objectives: (1) to identify the factors of SFTSV based on data from seven provinces with SFTSV cover and other provinces that had no reported cases; (2) to predict high-risk areas in China.…”

“…The epidemiology, clinical signs and pathogenesis of SFTS have been widely studied [18,19,20,21,22], and over 200 individual nucleotide sequences of SFTSV have been submitted to GenBank. However, the transmission of SFTSV remains an important and yet unexplained process.…”

Vertebrate Host Susceptibility to Heartland Virus

“…Infection with this virus shows a case-fatality rate of ≈12% in humans ( 5 , 6 ). Severe disease progression of patients infected with SFTSV has further been associated with increased cytokine and chemokine responses ( 7 ) and increased viremias throughout the course of disease ( 6 ).…”