Abstract
BackgroundCases of severe fever with thrombocytopenia syndrome (SFTS) have increasingly been observed in Miyazaki, southwest Japan. It is critical to identify and elucidate the risk factors of infection at community level. In the present study, we aimed to identify areas with a high risk of SFTS virus infection using a geospatial dataset of SFTS cases in Miyazaki.MethodsUsing 10 × 10-km mesh data and a geographically weighted logistic regression (GWLR) model, we examined the statistical associations between environmental variables and spatial variation in the risk of SFTS. We collected geospatial and population census data as well as forest and agriculture mesh information. Altitude and farmland were selected as two specific variables for predicting the presence of SFTS cases in a given mesh area.ResultsUsing GWLR, the area under the receiver operating characteristic curve (AUC) was estimated at 73.9%, outperforming the classical logistic regression model (72.4%). The sensitivity and specificity of the GWLR model were estimated at 90.9 and 58.7%, respectively. We identified altitude (odds ratio (OR) = 0.996, 95% confidence interval (CI): 0.994–0.999 per one-meter elevation) and farmland (OR = 0.999, 95% CI: 0.998–1.000 per % increase) as useful negative predictors of SFTS cases in Miyazaki.ConclusionsOur study findings revealed that the risk of SFTS is high in geographic areas where farmland area begins to diminish and at mid-level altitudes. Our findings can help to improve the efficiency of ecological and animal surveillance in high-risk areas. Using finer geographic resolution, such surveillance can help raise awareness among local residents in areas with a high risk of SFTS.
Highlights
Cases of severe fever with thrombocytopenia syndrome (SFTS) have increasingly been observed in Miyazaki, southwest Japan
We examined the area under the receiver operating characteristic (ROC) curve (AUC), along with the positive predictive value (PPV) and negative predictive value (NPV)
An SFTS case was observed for the first time in 2017 only in mesh units overlapping with Takaharu town, which had no previously reported cases; otherwise, all mesh areas had at least one reported case prior to 2017
Summary
Cases of severe fever with thrombocytopenia syndrome (SFTS) have increasingly been observed in Miyazaki, southwest Japan. We aimed to identify areas with a high risk of SFTS virus infection using a geospatial dataset of SFTS cases in Miyazaki. Severe fever with thrombocytopenia syndrome (SFTS) is a fatal tick-borne viral disease that involves thrombocytopenia, caused by the SFTS virus (SFTSV), a phlebovirus in the order Bunyavirales [1, 2]. The frequency and geographic areas at risk of tick-borne infectious diseases are known to have expanded in North America, possibly caused by ecological changes of tick abundance that are possibly induced by climate change [18]. The case fatality risk (CFR) among confirmed cases was about 30% in 2013 [4]; since both the CFR and absolute number of deaths have steadily decreased in Japan (e.g., of a total 72 cases in 2018, 3 deaths occurred, with a CFR about 5%) [24]
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