Exposure to ambient high temperature and increased risk of hospitalisation for non-infectious bowel diseases during 2000-2019: a case-crossover study in 1816 Brazilian cities.

Objectives: Although human intestine is sensitive to high ambient temperature, the heat-related morbidity burden remains rarely explored. This study quantified the association between high ambient temperature and non-infectious bowel disease (NBD) hospitalisations in Brazil during 2000-2019-a country experiencing substantial threats both from global warming and NBDs.

Methods: Daily data on weather and NBD hospitalisations were collected from 1816 cities. A time-stratified case-crossover design was used to assess the effect size of ambient temperature during the hot season. Stratified analysis by regions, population subgroups and disease types was performed.

Results: For each 5℃ increase in mean daily temperature, the cumulative OR of NBD hospitalisation over lag 0-3 days was 1.042 (95% CI 1.031 to 1.054) at the national level, reaching the maximum in the northeast and the minimum in the southeast. Assuming a causal relationship, ambient heat exposure explained 12.09% (95% CI 8.69% to 15.09%) of the total hospitalisations. The effect size was the highest in the youth, with no significant gender difference observed. Inflammation-related and function-related NBDs showed significantly higher susceptibility compared with other types of NBDs. The cumulative effect of ambient high temperature attenuated over the 20 years and from early to late hot season, suggesting both long-term and intraseasonal adaptations to heat.

Conclusions: The spatial, temporal and demographic variations in the strength of association should be considered for the development of health preventive strategies towards extreme ambient heat.