Impact of symptomatic comorbidities on heatstroke outcomes: A retrospective nationwide cohort study.

With global temperatures rising due to climate change, heatstroke is emerging as a public health concern, particularly among older adults. The population of Japan is aging, with heatstroke causing frequent hospitalizations and deaths. This study investigated the impact of symptomatic comorbidities, including cardiovascular, pulmonary, and renal disorders, on prognosis of heatstroke. Data were collected from 2,373 adult patients diagnosed with heat-related illnesses during 2017–2021 across multiple centers in Japan. Among them, 608 patients (25.6%) had at least one comorbidity. Patients were compared based on the presence and number of comorbidities. Statistical analyses, including logistic regression and Kaplan–Meier survival curves after propensity-score matching, were performed to evaluate the relationship between comorbidities and in-hospital mortality. The results showed significantly higher in-hospital mortality among patients with comorbidities compared to those without (15.3% vs. 10.9%, p = 0.005). Although mortality was higher in those with multiple comorbidities, the difference was not statistically significant. Respiratory comorbidities emerged as a significant risk factor for heatstroke-related mortality (odds ratio = 2.93, 95% CI = 1.53 – 5.61). Survival analysis further demonstrated a lower survival probability in patients with comorbidities, suggesting that symptomatic comorbidities, particularly respiratory diseases, notably influenced heatstroke outcomes and require focused preventive strategies.