Paper Memo: Individual Risk Factors for Swimming-Induced Pulmonary Edema in Open Water Swimmers: A Case-Control Study

1. Paper Title

Individual Risk Factors for Swimming-Induced Pulmonary Edema in Open Water Swimmers: A Case-Control Study

2. Citation

Chest. 2026; doi:10.1016/j.chest.2026.02.039

3. Summary of the Paper

This study is a case-control study aimed at identifying individual risk factors for swimming-induced pulmonary edema (SIPE) that occurs during open water swimming (OWS). It compared 258 patients diagnosed with SIPE (case group) and 2,117 individuals in a control group between 2017 and 2024 at a large-scale OWS event in Sweden (Vansbrosimningen). The diagnosis of SIPE was primarily based on lung ultrasound or specific clinical algorithms.

The analysis confirmed that known risk factors—female sex, age 40 or older, hypertension, heart disease, and recent respiratory infections—are independent risk factors. Furthermore, this study identified new risk factors: asthma and lack of OWS experience (fewer than five practice sessions in the current season). Notably, a higher frequency of prior open water practice was associated with a lower risk. This study emphasizes the importance of pre-event education and risk management for patients with asthma and novice swimmers.

4. Critical Appraisal

Internal Validity A strength of this study is the use of lung ultrasound, an objective diagnostic tool, to define SIPE, which ensures the accuracy of the clinical diagnosis. The analysis employed multivariate logistic regression and sensitivity analysis to statistically adjust for major confounding factors such as age, sex, and pre-existing conditions. On the other hand, the questionnaire response rate for the control group was low at 22%, and the possibility of selection bias cannot be ruled out, as individuals with higher health awareness or those who completed the swim were more likely to respond. Additionally, data such as past symptoms and practice frequency were based on self-reporting, which may introduce recall bias. Furthermore, some cases were diagnosed based on clinical criteria during certain periods, leading to slight limitations in the consistency of diagnostic criteria.

External Validity While many previous studies have focused on military personnel or elite triathletes, the findings obtained from a cohort of over 50,000 individuals, including recreational-level swimmers, have extremely high generalizability to general sports settings. However, this study was conducted in a cold-water environment with an average water temperature of 18°C in Sweden, and under conditions where most participants wore wetsuits. Therefore, it is unclear whether the same risk ratios would hold in regions with higher water temperatures, environments where wetsuits are not worn, or populations with different racial compositions. In particular, regarding the association between asthma and SIPE, it is necessary to consider the possibility that exposure to cold air or cold water may trigger asthma symptoms, and verification in other environments is awaited.