Unveiling heat vulnerability of older adults: an assessment of emergency hospital admissions in Switzerland.

Background Older adults are highly vulnerable to heat, yet how individual characteristics modulate its effects remains unclear. We assessed heat-related emergency hospital admission (EHA) risk across subpopulations of older adults receiving home care services in Switzerland (2019-2022).Methods We analysed patient-level EHA data linked to daily maximum temperature by MedStat regions of residence. We employed a case time series design with quasi-Poisson regression and distributed lag non-linear models to examine heat-related EHA risk, stratifying by individual characteristics, including sociodemographic factors, pre-existing health conditions, primary diagnosis, and levels of dependency and social interaction.Results The overall heat-related EHA risk was 1.12 (95% confidence interval (CI): 1.04-1.20) (at 99th percentile vs minimum temperature percentile risk). Males (1.16; 1.04-1.29) generally showed higher heat-related EHA risk than females (1.09; 0.98-1.20), except among those aged ≥85 years (females 1.16; 1.00-1.34 vs males 1.06; 0.90-1.26). Regarding functional capacity, females requiring assistance with daily tasks had an increased heat-related EHA risk, whereas males showed the opposite trend, with higher risk among those who were independent. Sex-specific analyses revealed that anxiety and dementia/Alzheimer's disease were risk factors for females, whereas cancer, chronic obstructive pulmonary disease, and coronary heart disease were risk factors for males. Joint stratification by pre-existing health conditions and primary diagnosis showed that individuals with pre-existing cancer had higher risks of admission for circulatory, genitourinary, infectious, and endocrine/metabolic causes during heat exposure.Conclusion Our results show that older individuals are not equally vulnerable to heat, underscoring the need for targeted public health interventions to protect high-risk older adults.