Impact of Daily Average Temperature on Annual Incidence of Scrub Typhus for Predicting

Abstract

Background: Scrub typhus is an acute febrile infectious disease. It is one of the most prevalent vector borne disease and occurs most frequently from October to December in Korea. The incidence of scrub typhus in Korea has shown rapidly increasing trend last decades and over 10,000 cases were reported in 2013. Weather variables are potential predictors of scrub typhus incidence. Predicting annual incidence of scrub typhus before autumn facilitates early public health responses to minimize morbidity. This study explored the impact of daily average temperature on the outbreak of scrub typhus in Korea. Methods: Analysis was performed using data on monthly weather variables and notified annual cases of scrub typhus in 68 cities, Korea from 2001 to 2008. Cities are categorized according to average annual incidence from 2001 to 2008 (High incidence area: average annual incidence >30 cases/100,000 persons, medium incidence area: 10-30 cases/100,000 persons, low incidence area: 0-10 cases/100,000 persons). A Poisson generalized estimating equations (GEE) model was used to estimate the impact of daily average temperature in the summer season on annual incidence of scrub typhus. Results: For high incidence area, medium incidence area and low incidence area, the average incidence per year was increased by 31% [95% confidence interval (CI): 15, 49%], 37% [95% CI: 22, 54%] and 28% [95% CI: 11, 48%] for a 1 degrees C increase in daily average temperature in August after controlling for potential confounding effects of precipitation and humidity. Daily average temperature, precipitation and humidity of other months like June, July in summer season did not impact on annual incidence for predicting. Conclusions: These findings suggest that daily average temperature in August have a considerable impact on annual incidence of scrub typhus in Korea for predicting before coming of autumn as outbreak season.