Spatial epidemiological determinants of severe fever with thrombocytopenia syndrome in Miyazaki, Japan: a GWLR modeling study

Abstract

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.

Serological and molecular survey of tick‐borne zoonotic pathogens including severe fever with thrombocytopenia syndrome virus in wild boars in Miyazaki Prefecture, Japan

“…These findings highlight not only the importance of differential diagnosis, but also the potential necessity of raising predictive public awareness of SFTS, especially in areas where no SFTS cases have been reported but other TBDs have been reported. In addition to known risk factors associated with SFTSV infection, such as occupational and geographical risks identified in previous studies (Ding et al., 2014 ; Liang et al., 2014 ; Yasuo & Nishiura, 2019 ), further studies on the distributional overlap of different TBD‐causing pathogens will provide valuable insights into the ecology of SFTSV from the aspect of potential transmission opportunities.…”

“…Miyazaki Prefecture, located in the southwest coastal area of Japan, is one of the hotspots for SFTS‐related death, with the largest reported case number, accounting for 14% (72 of 517) of all cases in Japan. These cases were found throughout this prefecture, especially along the boundary between the mountainous area and the plain (Yasuo & Nishiura, 2019 ). Miyazaki Prefecture is also an endemic area for other tick‐borne diseases (TBDs), including Japanese spotted fever and scrub typhus (Tsutsugamushi disease) caused by Rickettsia japonica (Rj) and Orientia tsutsugamushi (Ot), respectively (Mahara, 1997 ; Matsui et al., 2009 ).…”

“…These cases were found throughout this prefecture, especially along the boundary between the mountainous area and the plain (Yasuo & Nishiura, 2019). Miyazaki Prefecture is also an endemic area for other tick-borne diseases (TBDs), including Japanese spotted fever and scrub typhus (Tsutsugamushi disease) caused by Rickettsia japonica (Rj) and…”

Vectors, Hosts, and the Possible Risk Factors Associated with Severe Fever with Thrombocytopenia Syndrome

“…The SFTS epidemic curve revealed that 83.7% cases occurred between May and July [ 58 ], which is consistent with local agricultural activities and the seasonal abundance of ticks. One study showed that the risk of SFTS was high in geographic areas where the farmland area begins to diminish and at midlevel altitudes [ 61 ].…”