Occupational related heat stress exposure and heat-related symptoms among sugarcane workers in Thailand

Abstract Objective Thai sugarcane workers often work in very hot, humid conditions. This study investigated the effect of heat stress exposure on heat-related symptoms and severe heat-related symptoms associated with heat stroke in Thai sugarcane workers. Methods Sugarcane workers in Nakhon Sawan Province, Thailand, recruited during cooler and hotter months of 2023 provided information on demographics, health behaviours, working conditions, and 21 heat-related symptoms, including 8 severe heat-related symptoms. Environmental heat was assessed using Wet-Bulb Globe Temperature (WBGT). Full shift time-weighted average effective WBGTs (WBGT eff -FS-TWA) were estimated and adjusted for clothing to represent heat stress exposure. Associations between heat stress exposure and symptom counts were examined using generalised negative binomial regression, adjusting for available confounders. Generalised binary logistic regression assessed associations between heat stress exposure and having ≥ 10 heat-related symptoms or ≥ 3 severe heat-related symptoms. Results The mean measured WBGT was 28.9 ± 2.6 °C. The mean WBGT eff -FS-TWA was 31.3 ± 2.8 °C, with more than 40% exposed to 32.0–34.0 °C. Of the 295 participants (165 males, 130 females), there were no significant gender differences observed in the risk of heat-related symptoms. Ninety-eight percent experienced ≥ 1 heat-related symptom, and 74% reported ≥ 1 severe heat-related symptom. Relative risk (RR (95%CI)) for the number of heat-related symptoms was 1.10 (1.08, 1.13) per 1 °C increase in WBGT eff -FS-TWA, whereas for severe heat-related symptoms, the RR was 1.19 (1.14, 1.24). Odds ratio (OR) for ≥ 10 heat-related symptoms was 1.50 (1.29, 1.75) per 1 °C; for ≥ 3 severe heat-related symptoms OR was 1.49 (1.30, 1.72). Conclusion Sugarcane workers in Thailand report very high prevalence of heat-related symptoms. The number of reported heat-related and severe heat-related symptoms increases significantly as temperature increases. These results highlight the urgent need to protect sugarcane and other agricultural workers from excessive heat stress.