Incidence of Swimming-Induced Pulmonary Edema: A Cohort Study Based on 47,600 Open-Water Swimming Distances

Abstract

Background: Despite increasing awareness of swimming-induced pulmonary edema (SIPE), large population-based studies are lacking and the incidence is unknown.

Research question: What is the incidence of SIPE in a mixed group of competitive and recreational swimmers during a large open-water swimming event?

Methods: In four consecutive years (2016-2019), a prospective cohort study was conducted during Sweden's largest open-water swimming event, Vansbrosimningen. All swimmers seeking medical care with acute respiratory symptoms were eligible for the study. SIPE diagnosis was based on clinical findings in 2016 and 2017 and pulmonary edema assessed by lung ultrasound in 2018 and 2019. Data on patient characteristics, clinical findings, and information about the race were collected.

Results: Based on 47,573 consecutive swimming distances, 322 patients with acute respiratory symptoms (0.68%; CI, 0.61%-0.75%) were treated at the mobile medical unit. Of these, 211 patients (0.44%; CI, 0.39%-0.51%) received a diagnosis of SIPE. The annual incidence of SIPE was 0.34%, 0.47%, 0.41%, and 0.57%, respectively, from 2016 through 2019. Most patients diagnosed with SIPE were women (90%), despite about equal percentages of men and women participating (47% men and 53% women). The incidence of SIPE overall was 0.75% in women and 0.09% in men. The incidence increased with age, from 0.08% in the youngest age group (18-30 years) to 1.1% in the oldest age group (≥ 61 years). Based on multiple logistic regression analysis, the adjusted odds for SIPE occurring was 8.59 times higher for women compared with men and 12.74 times higher for the oldest age group compared with the youngest age group.

Interpretation: The incidence of SIPE over 4 years during a large open-water swimming event in Sweden was 0.44%. The incidence was higher in women than in men and increased with age.

Keywords: SIPE; immersion pulmonary edema; incidence; lung ultrasound; swimming; swimming-induced pulmonary edema.

Graphical abstract

Figure 1

Study flow chart showing the total number of swimming races (by those ≥ 18 years of age) during Vansbrosimningen in 2016, 2017, 2018, and 2019. Patients seeking medical attention for respiratory symptoms (dyspnea, cough, or both) were eligible for the study. The numbers of patients who received a diagnosis of SIPE are reported together with sex distribution for each year. SIPE = swimming-induced pulmonary edema.

Figure 2

A, B, Age- and sex-dependent incidence of SIPE. Cumulative incidence reported for men and women (A) and by age group (B) as follows: 18 to 30 years, 31 to 40 years, 41 to 50 years, 51 to 60 years, and 61 years or older. SIPE = swimming-induced pulmonary edema.

Figure 3

Box-and-whisker plot showing the peripheral saturation (%) presented for all patients who received a diagnosis of swimming-induced pulmonary edema at the mobile medical unit in 2016, 2017, 2018, and 2019. Peripheral saturation measured by pulse oximeter at admission. Overall comparison between years made by Kruskal-Wallis test (P = .0023). P values for postdoc analysis was carried out using Dunn’s test: P = .002 (2016 vs 2019), P = .049 (2017 vs 2019), P = .062 (2018 vs 2019), and P > .100 (2016 vs 2017, 2016 vs 2018, and 2017 vs 2018).