Risk factors for SIPE: a case-control study of 978 open-water swimmers

Background: SIPE (swimming induced pulmonary oedema) can be life threatening, however, evidence on what can be done to reduce the risk of it is limited.

Objectives: The aim of this study was to investigate risk factors for SIPE.

Methods: We conducted a case-control study of swimmers recruited through online open water swimming communities and outdoor swimming events. We asked about symptoms while swimming, demographics, height, weight, medical history, swimming habits and health behaviours. Participants were considered to have SIPE if they reported shortness of breath (SOB) out of proportion to effort while swimming, that did not occur immediate after water entry and was not associated with water aspiration, or they had been told they had had SIPE by a doctor. Cases were compared to controls who reported never having had SOB whilst swimming. We calculated odds ratios (ORs) and 95% confidence intervals (CI) for risk factors controlling for other factors.

Results: The study included 107 cases and 871 controls. Risk factors for SIPE included wearing a wetsuit compared to no wetsuit (tight wetsuit: adjusted OR 6.56 (95% CI 3.50 to 12.30); non-tight wetsuit: adjusted OR 2.10 (95% CI 1.27 to 3.48)). Having asthma was associated with SIPE (OR 2.70, 95% CI 1.73 to 4.21). The associations were robust to attempts to control for factors such as water temperature, effort levels, age and sex. Age, sex, swimming distance, maximum effort levels or cardiovascular disease were not associated with SIPE.

Interpretation: People who wear a wetsuit during outdoor swimming are much more likely to report SIPE than people who do not. It is important to further explore whether the association is causal and what the mechanisms might be. If the association is found to be causal, it may be necessary to address wetsuit design to prevent SIPE.