CDC: Why Strong Swimmers Drowned

Unexplained drowning deaths in healthy swimmers may be due to deliberate breath-holding either in contests or as part of rigorous, self-imposed training regimens, a new report concludes.

A series of mysterious New York State drownings of healthy young men—including one who had hopes of qualifying for US Navy SEAL training—sparked a state Department of Health investigation.

In a report on the phenomenon in the May 22 edition of the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report New York City Department of Health and Mental Hygiene investigators Christopher Boyd, Amanda Levy, Trevor McProud, Lilly Huang, Eli Raneses and Carolyn Olson call the drownings cases of dangerous underwater breath-holding behaviors (DUBBS).

The team identified 16 DUBBS cases leading to drowning, 3 in New York City, not all of which ended in deaths. The incidents were all observed by others and nearly all (15) occurred in swimming pools. But the authors stress that there are likely many more drownings and drowning deaths that go unreported and unobserved. “More than half of drowning incidents are not witnessed,” they noted.

In all cases, the swimmers engaged behavior that led to breath-hold blackout, putting themselves at risk of drowning by decreasing the body’s stores of CO2 and partial pressure of CO2 delaying the cerebral response that would normally cause a swimmer to come to the surface to breathe.

The blackout results in hypoxia and loss of consciousness underwater, but the fact that the drowning was triggered by this deliberate risk-taking behavior often goes unreported, the team wrote.

Four fatal cases involved intentional hyperventilation before or during submergence or swimming. That behavior resulted in death for two healthy men who were performing strenuous exercises to prepare for an “advanced military fitness test,” the team wrote. Lifeguards administered CPR but it did not revive them.

In others swimmers played “breath-holding games” often staying motionless while they did. The report cited a case of a healthy teenager who was engaged in such a competition as part of horseplay with his friends. When the friends were unable to revive him they called a lifeguard but it was too late and he too died.

There were also cases were the swimmers were doing hypoxic training, defined as prolonged underwater distance swimming or extended breath-holding intervals. One case involved a teenager, an advanced swimmer who worked as a lifeguard and had a goal of becoming a Navy SEAL. Staff at the pool reported seeing him submerging himself for extended periods of time, and swimming laps underwater. He lost consciousness and could not be revived.

New York City health officials launched a public education campaign to discourage DUBBS. The CDC report suggests more could be done on the national level. “Drowning continues to present a public health risk, even in facilities that have adequate lifeguards and other safety precautions,” the authors note.