To Örebro University

BACKGROUND: Despite increasing awareness of swimming-induced pulmonary edema (SIPE), there is a lack of large population-based studies 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 2016-2017 and pulmonary edema assessed by lung ultrasound in 2018-2019. Data on patient characteristics, clinical findings and information about the race were collected.

RESULTS: Based on 47 573 consecutive swimming distances, 322 cases of acute respiratory symptoms (0.68%; C.I. 0.61%-0.75%) were presented at the mobile medical unit. Of these, 211 (0.44%; C.I. 0.39%-0.51%) were diagnosed with SIPE. The annual incidence of SIPE was 0.34%, 0.47%, 0.41% and 0.57%, respectively in 2016-2019. A majority of patients diagnosed with SIPE were women (90%) despite about equal percentage of men and women participating (47% men; 53% women). The incidence of SIPE was overall 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 acquiring SIPE was 8.59 times higher for women compared to men and 12.74 times higher for the oldest age group compared to the youngest.

INTERPRETATION: The incidence of SIPE over four 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 higher age.