How had climate variability affected the scrub typhus incidence in South Korea?

Abstract

BACKGROUND AND AIM: Climate change such as global warming unexpectedly compromised human health in particular increased incidence of infectious diseases. We aimed to investigate the long-term effects of climate variability on the scrub typhus incidence in South Korea. METHODS: Meteorological variables were conjoined with scrub typhus cases reported from 2001 to 2019 in South Korea. Generalized additive model was used to explore the non-linearity of the lagged association between meteorological variables and weekly scrub typhus incidence. Then, modified generalized linear models were used to estimate weekly incidence changes beyond the identified thresholds of mean ambient temperature and relative humidity. Further, increases in annual average temperature and the number of heatwave days were linearly regressed for scrub typhus cases from September to December. RESULTS:Mean ambient temperature and relative humidity above thresholds were linearly associated with the scrub typhus incidence with a simple lag of 15 weeks. Thresholds of mean ambient temperature and relative humidity ranged from 8.0°C to 11.6°C and from 29.7% to 65%, respectively. An increase in weekly incidence from September to December ranged from 11.2% (95% CI: 8.7, 13.8) to 35.7% (95% CI: 29.6, 42.1) per 1°C elevation in mean ambient temperature from June to August. Compared to the past 30 years’ averages, mean ambient temperature elevated and the number of annual heatwave days increased. Scrub typhus cases between September and December increased by 481 (95% CI: 377, 585) per 1°C increase in mean ambient temperature, and by 406 (95% CI: 393, 419) as the annual number of heatwave days increased. CONCLUSIONS:Mean ambient temperature elevation and relative humidity increase in the summer was associated with the increased incidence of scrub typhus in the fall. Increased annual average temperature and the number of heatwave days for the last 19 years were associated with increased scrub typhus cases in a peak period. KEYWORDS: climate change, temperature, humidity, scrub typhus, infections