[Meteorological factors and related lag effects on scrub typhus in southwestern Yunnan]

Objective: To analyze the influence and related lag effects of meteorological factors on scrub typhus (ST) in southwestern Yunnan, to provide a reference for the corresponding prevention and treatment measures. Methods: Data on ST and meteorology in Yunnan province from 2007 to 2018 were collected. A distributed lag nonlinear model was conducted to study the cumulative lag effects of temperature, relative humidity, and rainfall on ST. Results: From 2007-2018, a total of 19 975 ST cases were reported in southwestern Yunnan. Weekly mean temperature, mean relative humidity, and the risk of ST all showed J-shaped curves. The cumulative risk of ST increased with mean temperature >23 ℃, mean relative humidity >80%, and cumulative rainfall between 20 and 60 mm or over 100 mm, weekly. Taking the median value as the reference, higher temperature (22.27 ℃, 23.45 ℃), relative humidity (80.14%, 84.38%) and rainfall (37.17 mm, 74.42 mm) all increased the risk of disease while lower temperature (11.22 ℃,14.83 ℃), relative humidity (53.18%,65.36%) and rainfall (0.00 mm,0.55 mm) showed opposite effects. The temperature-lag effect lasted for 10 and 16 weeks, respectively, with ST's risk the highest during the week of exposure. Humidity-lag effects usually last for 10 and 17 weeks. The lag effect of rainfall lasted for 25 weeks, while the disease's risk was the highest in the 4^th week. Conclusion: Factors as temperature, relative humidity, and precipitation showed nonlinear and lag effects on ST. High temperature, high relative humidity, and an appropriate amount of rainfalls increase the risk of ST. The authorities of public health should implement effective prevention and control measures according to meteorological conditions.