Spatiotemporal Dynamics of Scrub Typhus Transmission in Mainland China, 2006-2014

Background: Scrub typhus is endemic in the Asia-Pacific region including China, and the number of reported cases has increased dramatically in the past decade. However, the spatial-temporal dynamics and the potential risk factors in transmission of scrub typhus in mainland China have yet to be characterized. Objective: This study aims to explore the spatiotemporal dynamics of reported scrub typhus cases in mainland China between January 2006 and December 2014, to detect the location of high risk spatiotemporal clusters of scrub typhus cases, and identify the potential risk factors affecting the re-emergence of the disease. Method: Monthly cases of scrub typhus reported at the county level between 2006 and 2014 were obtained from the Chinese Center for Diseases Control and Prevention. Time-series analyses, spatiotemporal cluster analyses, and spatial scan statistics were used to explore the characteristics of the scrub typhus incidence. To explore the association between scrub typhus incidence and environmental variables panel Poisson regression analysis was conducted. Results: During the time period between 2006 and 2014 a total of 54,558 scrub typhus cases were reported in mainland China, which grew exponentially. The majority of cases were reported each year between July and November, with peak incidence during October every year. The spatiotemporal dynamics of scrub typhus varied over the study period with high-risk clusters identified in southwest, southern, and middle-eastern part of China. Scrub typhus incidence was positively correlated with the percentage of shrub and meteorological variables including temperature and precipitation. Conclusions: The results of this study demonstrate areas in China that could be targeted with public health interventions to mitigate the growing threat of scrub typhus in the country. Author Summary: Scrub typhus is a vector-borne disease carried by the chigger mite and is endemic in the Asia-Pacific region. Now scrub typhus causes a considerable burden on public health and the economy in China. We explored the spatiotemporal dynamics of scrub typhus cases in China between January 2006 and December 2014, and explored the potential risk factors affecting the spatial distribution of the disease. The majority of cases were reported between July and November, with peak incidence during October every year. Several high-risk clusters were identified in southwest, southern, and middle-east China. Scrub typhus incidence was positively correlated with the percentage of shrub, and temporal variation in temperature and precipitation in China.