Avalanche Survival Rates in Switzerland, 1981-2020.

Importance: Survival probability among individuals critically buried by avalanche is highly time dependent, which was demonstrated 30 years ago. However, it remains unclear whether avalanche survival probability has changed over time. Objective: To assess the avalanche survival rate and probability as well as the rescue probability over the past 4 decades. Design, Setting, and Participants: In this cohort study, avalanche data from Switzerland that were collected by the WSL Institute for Snow and Avalanche Research (SLF) in Davos were analyzed from the winter beginning in 1981 to that beginning in 2020 and compared with data from the period 1981 to 1990. Data were analyzed from January to April 2024. Exposure: Critical avalanche burial (ie, burial involving the head and chest). Main Outcomes and Measures: Survival rate among individuals critically buried by avalanche, survival probability, and rescue probability in relation to time buried under the avalanche. Results: The study included 1643 individuals critically buried by avalanche (mean [SD] age, 37 [13.7] years; 1090 of 1342 with known sex [81.2%] were male) among 3805 avalanches involving 7059 persons. Compared with the period from 1981 to 1990, the total survival rate over the full study period increased from 43.5% (95% CI, 38.8%-48.3%) to 53.4% (95% CI, 51.0%-55.8%). Survival probability remained high at 91% (95% CI, 80%-100%) for rescue during the first 10 minutes but then decreased to 31% (95% CI, 11%-51%) for rescue between 10 and 30 minutes. The survival rate among those buried long term (>130 minutes) increased from 2.6% (95% CI, 0.7%-6.9%) to 7.3% (95% CI, 4.8%-10.7%). The median rescue time decreased from 45 (IQR, 15-148) minutes to 25 (IQR, 10-85) minutes. Survival rates among individuals rescued from avalanche by organized rescue teams increased from 14.0% (28 of 200) to 22.9% (161 of 704). Conclusions and Relevance: This cohort study of 1643 individuals critically buried by avalanche found that over the past 4 decades, total survival rates considerably increased and rescue times decreased. Survival rates among those buried long term (>130 minutes) also increased. These findings are likely attributable to collaborative efforts among stakeholders to enhance avalanche search-and-rescue techniques and medical interventions.