Projecting long-term excess risks of major infectious diseases associated with future extreme weather events in Thailand

Climate change is postulated to impact infectious disease transmission, yet few studies have characterised the excess risks of infectious diseases associated with extreme weather events. To address this, we conducted a study estimating and projecting the impacts of extreme heat and precipitation on the incidence of major infectious diseases in Thailand. We developed, fitted and validated an analytical framework to model province-level disease cases and their relationship with extreme weather indicators based on historical data. We used generalised additive models to delineate the relationship between monthly extreme heat days, standardised precipitation index and incidence rates of seven infectious diseases (dengue, malaria, Japanese encephalitis, melioidosis, leptospirosis, pneumonia, influenza) across Thailand's provinces. Disease-specific models were fitted to historical surveillance data and used to project future disease incidence across 4 Shared Socioeconomic Pathways (SSP) based on MIROC6 climate projections. Historically, extreme heat was associated with an increase in all infectious disease incidences except malaria and leptospirosis. We projected that dengue risk declines in most future climate change scenarios, except SSP245 where extreme heat drives a significant rise in Northern and Central Thailand from 2021-2060. Nationwide dengue risk is expected to decrease by 24.9% (95%CI:9.68%,40.0%) during future periods of extreme weather from 2061-2080 compared to historical baselines. Influenced by heat and dry weather in Northeastern and Central regions, influenza risk is expected to increase under SSP245 in 2021-2060, then decrease with extreme precipitation. Influenza risk in Nakhon Ratchasima is expected to increase by 36.8% (95%CI:9.83%,63.8%) in 2021-2040 under SSP245. Localised public health interventions are necessary to address climate change impacts.