# Spatiotemporal evolution and impacts of environment on scrub typhus in northern China, 2006–2019

## TL;DR

This study examines how scrub typhus cases in Shandong, China, changed over time and how environmental factors influenced their spread.

## Contribution

The study identifies key environmental factors influencing scrub typhus and highlights humidex as a useful indicator for predicting outbreaks.

## Key findings

- Scrub typhus cases peaked in 2014 and were concentrated in Linyi and Rizhao cities.
- Environmental factors like vegetation, land relief, and humidex strongly correlate with scrub typhus distribution.
- Humidex is a better composite indicator than individual meteorological variables for predicting scrub typhus incidence.

## Abstract

Scrub typhus is a significant public health issue with a global distribution. In northern China, Shandong Province is a major endemic area, but its spatiotemporal patterns and influencing factors remain unclear.

This study collected data on scrub typhus in Shandong Province from the Infectious Disease Reporting System of the Shandong Center for Disease Control and Prevention between 2006 and 2019. Spatiotemporal evolution analysis combined joinpoint regression, spatiotemporal cluster analysis and standard deviation ellipse. GeoDetector was used to identify the impacts of socioeconomic and natural factors on spatial distribution of scrub typhus. Generalised additive model was applied to explore associations with meteorological variables.

9397 scrub typhus cases were reported in Shandong Province from 2006 to 2019, with an average annual incidence of 0.68 / 100 000, peaking in 2014 (1.53 / 100 000). Cases were concentrated from September to November. Spatiotemporal cluster was mainly in Linyi and Rizhao cities in southern Shandong. The centre of gravity of scrub typhus gradually shifted southeast, and moved back from 2015 to 2019. Nighttime light (q = 0.223), normalised difference vegetation index (q = 0.197), relief degree of land surface (q = 0.230), grassland (q = 0.320), and water (q = 0.180) were all related with scrub typhus, with q indicating the explanatory power of each factor on the spatial distribution of the disease. The strongest relative risks between monthly incidence of scrub typhus and temperature, humidity, precipitation and humidex were 1.528 (lag3), 1.175 (lag3), 1.013 (lag1), and 1.279 (lag3), respectively.

Scrub typhus in Shandong Province was mainly concentrated in Linyi and Rizhao cities. The occurrence of scrub typhus is influenced by various environmental factors. Humidex is a better composite indicator to reflect the impacts of meteorological factors on scrub typhus in northern China. These findings provide scientific evidence to guide prevention and control strategies for scrub typhus. Limitations include potential underreporting in surveillance data and the absence of vector and host information.