Just when you thought it was safe to go back into the water, doctors are warning about a relatively little-known hazard linked to open water swimming, fluid on the lungs.
Otherwise known as pulmonary oedema, the condition has been reported in 1 to 2 per cent of open-water swimmers, according to the authors of a new study.
Older age, swimming long distances, cold water and being a woman are among the risk factors, as are high blood pressure and pre-existing heart disease. But it frequently occurs in those who are otherwise fit and healthy, the authors say.
They point to mounting evidence of the link between open-water swimming and swimming-induced pulmonary oedema, or SIPE for short, which leaves swimmers struggling to draw breath and depletes their blood of vital oxygen.
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The popularity of open-water swimming has soared since the Covid pandemic, with many enthusiasts continuing to swim year-round in spite of sea temperatures falling to as low as 6 degrees.
The study, published in the journal BMJ Case Reports, concerns a single case, a woman in her fifties who is a competitive long-distance swimmer and triathlete.
Otherwise fit and well, she was struggling to breathe and coughing up blood after taking part in an open-water swimming event at night in water temperatures of about 17 degrees while wearing a wetsuit.
On arrival at hospital, her heartbeat was rapid and a chest X-ray revealed pulmonary oedema. Further scans revealed that fluid had infiltrated the heart muscle, a sign of strain known as myocardial oedema. She had no structural heart disease.
Her symptoms settled within two hours of arrival at hospital and after monitoring, she was discharged the following morning. She has returned to full training.
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The doctors say it is not clear exactly what causes SIPE. Recurrence is common and has been reported in 13 to 22 per cent of scuba divers and swimmers, suggesting a predisposition to the condition, say the authors.
They advise swimming at a slower pace, accompanied, in warmer water, without a tightfitting wetsuit, and avoiding non-steroidal anti-inflammatories such as ibuprofen to minimise the risk.
For those experiencing symptoms for the first time, the authors recommend stopping swimming and getting out of the water straight away, then sitting upright, and calling for medical assistance if required.
