Who is more vulnerable among the most vulnerable? Assessing vulnerability profiles to heat in older adults in Switzerland

Background: Exposure to heat increases the risk of hospitalisation due to several causes, including cardiovascular and respiratory diseases and mental disorders. Older adults are especially vulnerable to heat, yet it is unclear which individuals are at a higher risk—for example, those with specific comorbidities (e.g., diabetes, Alzheimer’s), levels of dependency, or activity patterns. To address this knowledge gap, we assess the risk of emergency hospital admission (EHA) associated with heat among the older population of different characteristics during the warmer months (May to September) from 2019 to 2022 in Switzerland.

Methods: We collected individual-level EHA data linked to detailed health information gathered from homecare services (Spitex). For each admission, we calculated the population-weighted daily maximum temperature of the medical district of residence (Medstat regions) using 1km gridded temperature data. We employed an individual-level case time series design and assessed the association between EHA and heat using distributed lag non-linear models. We stratified the analysis by population subgroups according to individual characteristics, including comorbidities, levels of social interaction, and daily activity capacities.

Results: Overall, we observed a 13% increase in EHA risk during heat days (at the 99th temperature percentile, compared to the minimum hospitalisation temperature percentile [MHP]) (relative risk (RR): 1.13; 95% CI: 1.05-1.21). Older adults who did not receive assistance with daily activities and self-care had a higher risk of EHA than those receiving assistance. Furthermore, we observed that individuals with more frequent interactions with family members exhibited higher risk (1.15; 1.07-1.25) than those with low interaction levels (1.02; 0.84-1.23). A higher risk was also observed in individuals who spend less time alone (1.20; 1.10-1.32 vs. high time alone 1.02; 0.90-1.15)) and lived with a partner (1.26; 1.12-1.41 vs. living alone 1.05; 0.95-1.17). In terms of comorbidities, older individuals with cancer (1.36; 1.16-1.61), diabetes (1.15; 1.00-1.34), and dementia or Alzheimer’s disease (1.26; 1.05-1.51) had a higher risk of EHA associated with heat.

Conclusion: Our results indicate that individuals experienced varying EHA risks during heat days based on their self-care abilities, level of social engagement, and existing health conditions. These findings underscore the need for targeted public health measures considering individual risk factors.