The risk of hospitalization associated with foehn winds and temperature in the mountainous region of Switzerland

Foehn winds are intense warm winds, common in mountain regions, but their health impacts and potential to exacerbate existing heat-related risks remain poorly understood. This is particularly concerning for rural areas where older, heat-vulnerable individuals live. We investigated the independent and combined association of foehn winds and temperature with cause-specific emergency hospitalizations in Switzerland. We analyzed daily temperature, foehn winds intensity, and cause-specific hospitalizations near eight foehn wind-observing meteorological stations in Switzerland (1998-2019). We performed a case-time series analysis to examine the association between foehn winds intensity and hospitalization risk with and without temperature adjustment, and whether foehn winds amplify cold and heat-related hospitalizations with an interaction term between foehn winds and temperature. Foehn winds intensity showed small and no consistent association with hospitalizations in temperature-adjusted (0.4% [95% confidence interval: -1.1%, 1.8%] per 6 hours increase in daily full foehn winds intensity) and nonadjusted models (0.8% [-0.5%, 2.3%]). However, foehn winds may amplify heat-related hospitalization risk with a 14% (-3%, 33%) increase in risk at the 99th temperature percentile (vs. temperature of minimum risk) on foehn days, compared with -2% (-8%, 6%) on non-foehn days. The association was larger for females, older adults, and for hospitalizations due to respiratory and mental health causes. While foehn winds did not directly impact hospitalizations, they may contribute to an amplification of heat-related health risks, especially for females and older adults. Further research is needed to assess their effects in other regions, climates, and vulnerable populations.