Background Cases 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. Methods Using 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. Results Using 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. Conclusions Our 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. Electronic supplementary material The online version of this article (10.1186/s12879-019-4111-3) contains supplementary material, which is available to authorized users.

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A 58‐year‐old woman presenting with 3‐week‐prolonged fever was referred to our department. Her present history and physical examination results were unremarkable. Her activated partial thromboplastin time (APTT) was prolonged. Upon further investigation, anticardiolipin/beta2‐glycoprotein I complex antibodies (CL‐β2GPI) were detected, occasionally associated with syphilis. On day 14 of her fourth visit as an outpatient, serological tests confirmed the diagnosis, with newly appeared roseola on her palms and soles. She was in the transitional phase to secondary syphilis. Four months later, after successful treatment, her APTT was normalized with CL‐β2GPI negative. Syphilis should be considered in patients with APTT prolongation.

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