Background: With rising temperatures and an aging population, understanding how to prevent heat-related illness among older adults will be increasingly crucial. Despite biological plausibility, no study to date has investigated whether fine particulate matter air pollution (PM2.5) contributes to the risk of hospitalization with a diagnosis code indicating heat-related illness, referred to as heat-related hospitalization. This study aims to fill this gap by investigating the independent and combined effects of temperature and PM2.5 on heat-related hospitalization risk. Methods: We identified Medicare fee-for-service beneficiaries in the contiguous United States who experienced a heat-related hospitalization between 2008 and 2016. Using a case-crossover design and Bayesian conditional logistic regression, we characterized the associations of temperature and PM2.5 with heat-related hospitalization. We then estimated the relative excess risk due to interaction to quantify the additive interaction of simultaneous exposure to heat and PM2.5. Results: We observed 112,969 heat-related hospitalizations. Fixing PM2.5 at the case day median, the odds ratio for increasing temperature from its case day median to the 95th percentile was 1.05 (95% CI: 1.03, 1.06). Fixing temperature at the case day median, the odds ratio for increasing PM2.5 from its median to the 95th percentile was 1.01 (95% CI: 0.99, 1.04). The relative excess risk due to interaction for simultaneous median-to-95th percentile increases in temperature and PM2.5 was 0.03 (95% CI: 0.01, 0.06). Conclusions: Our study is the first to observe synergism between temperature and PM2.5 associated with the risk of heat-related hospitalization. These findings highlight the importance of considering air pollution in effective public health and clinical interventions to prevent heat-related illness.

翻译：背景：随着气温上升和人口老龄化，了解如何预防老年人热相关疾病将日益重要。尽管存在生物学合理性，但迄今为止尚无研究探讨细颗粒物空气污染（PM2.5）是否会增加诊断为热相关疾病的住院风险（即热相关住院）。本研究旨在通过探究温度和PM2.5对热相关住院风险的独立及联合效应来填补这一空白。方法：我们识别了2008年至2016年间美国本土地区经历热相关住院的医疗保险按服务付费受益人。采用病例交叉设计和贝叶斯条件逻辑回归，我们刻画了温度与PM2.5同热相关住院之间的关联。随后，我们通过估计交互作用导致的相对超额风险来量化同时暴露于高温与PM2.5的相加交互作用。结果：我们共观察到112,969例热相关住院事件。将PM2.5固定在病例日中位数水平时，温度从病例日中位数上升至第95百分位数的比值比为1.05（95% CI: 1.03, 1.06）。将温度固定在病例日中位数水平时，PM2.5从中位数上升至第95百分位数的比值比为1.01（95% CI: 0.99, 1.04）。温度与PM2.5同时从中位数上升至第95百分位数时，交互作用导致的相对超额风险为0.03（95% CI: 0.01, 0.06）。结论：本研究首次观察到温度与PM2.5在热相关住院风险中存在协同作用。这些发现强调了在制定有效的公共卫生和临床干预措施以预防热相关疾病时，考虑空气污染因素的重要性。