Retrospective analysis of spatiotemporal variation of scrub typhus in Yunnan Province, 2006-2022

Abstract

Background: Scrub typhus is a life-threatening zoonotic infection. In recent years, the endemic areas of scrub typhus have been continuously expanding, and the incidence rate has been increasing. However, it remains a globally neglected disease. Yunnan Province is a major infected area, and the study of spatiotemporal and seasonal variation scrub typhus in this region is crucial for the prevention and control of the disease.

Methods/results: We collected surveillance data on scrub typhus cases in Yunnan Province from 2006 to 2022. Using methods such as spatial trend analysis, Moran's I, and retrospective temporal scan statistics, the spatial and seasonal changes of scrub typhus were analyzed. The study period recorded 71,068 reported cases of scrub typhus in Yunnan Province, with the annual incidence rate sharply increasing (P<0.001). Approximately 93.38% of cases are concentrated in June to November (P = 0.001). Nearly 98.0% of counties were affected. The center of gravity of incidence migrates in a south and west direction. The incidence of scrub typhus was positively correlated spatially, and the spatial clustering distribution was significant. The most likely spatial cluster of cases (relative risk = 14.09, P<0.001) was distributed in Lincang, Dehong, Baoshan, Banna, and Puer. Significant positive correlations between the number of scrub typhus cases and average temperature, precipitation and relative humidity.

Conclusions: In Yunnan Province, scrub typhus is widely transmitted, with an increasing incidence, and it exhibits distinct seasonal characteristics (from June to November). The center of gravity of incidence has shifted to the south and west, with higher incidence rates observed in border regions. The risk clustering regions encompass all border prefectures. This pattern is significantly correlated with climatic factors such as average temperature, precipitation, and relative humidity. The relevant departments should strengthen the monitoring of scrub typhus, formulate prevention and control strategies, and provide health education to local residents.

Fig 1. Reported cases of scrub typhus in Yunnan Province, 2006–2022.

Aggregated number of cases by year (blue bars), annual incidence rate (orange line) per 100,000 population.

Fig 2. The seasonal distribution of scrub typhus cases in Yunnan Province.

Fig 3. The geographic distribution of the annual incidence of scrub typhus in Yunnan Province during 2006 to 2022.

(The county-level map of Yunnan Province used in our study was obtained from the Chinese Academy of Sciences, Institute of Geographic Sciences and Natural Resources Research(http://www.resdc.cn/). This platform allows you to download the required base maps free of charge by registering as a user).

Fig 4. Spatial trend analysis of the incidence of scrub typhus in Yunnan Province, 2006–2022 (Green line indicates west-east direction, blue line indicates north-south direction).

Fig 5. The gravity center migration trajectory of scrub typhus in Yunnan Province from 2006 to 2022.

(The county-level map of Yunnan Province used in our study was obtained from the Chinese Academy of Sciences, Institute of Geographic Sciences and Natural Resources Research(http://www.resdc.cn/). This platform allows you to download the required base maps free of charge by registering as a user).

Fig 6. Spatiotemporal clusters of scrub typhus in Yunnan Province, 2006–2022.

Light redindicates the most likely high-risk spatiotemporal clustering area, orange indicates the secondary-risk clustering area. (The county-level map of Yunnan Province used in our study was obtained from the Chinese Academy of Sciences, Institute of Geographic Sciences and Natural Resources Research (http://www.resdc.cn/). This platform allows you to download the required base maps free of charge by registering as a user).

Fig 7. The relationship between meteorological factors and the number of scrub typhus cases in Yunnan Province, 2006–2022.