How Worried Should Swimmers Be About Brain-Eating Amoebas?

Brain-eating amoebas might sound like the antagonist in a horror movie from the 1950s, but Naegleria fowleri—the scientific name for the amoeba—is very real.

In fact, it made recent headlines when a man died earlier this month after swimming in an Iowa lake, due to primary amebic meningoencephalitis (PAM), which is the infection caused by brain-eating amoeba. And that, unsurprisingly, has gotten open water swimmers and triathletes buzzing about the safety of swimming in the kind of warm, fresh bodies of water where this rare amoeba is most commonly found.

But how worried do we need to be about brain-eating amoebas? “Even though it is a very serious illness, cases are extremely rare, so the risk to individual swimmers is very low,” said Ian Young, epidemiology researcher at Toronto Metropolitan University.

Just how rare? The Centers for Disease Control and Prevention (CDC) has been tracking this in the U.S. since 1962, and in that time there have only been a total of 154 cases—but nearly all of them have been fatal. Texas, followed by Florida, has reported the most infections (40 and 36 known infections, respectively), with California, Arizona, and South Carolina all reporting eight or more infections.

And that makes sense, said Young. “The amoeba … prefers to live in warm, freshwater bodies (e.g., lakes and hot springs). It is most likely to be found in waters that are >30 degrees Celsius (86 degrees F), so in North America, cases have tended to occur more often in the southern U.S.”

However, he says, that doesn’t mean our neighbors up north are entirely risk-free, especially as climate change warms waters farther north. “[T]he CDC published a study last year that found a northward expansion of cases in recent decades, though the number of cases detected has not increased,” he said. “Therefore, with climate change and its projected effects on warming air and water temperatures, in future years we might expect cases to occur in more northern areas of the U.S. and in Canada where they previously haven’t been detected before.”

But, he notes, it’s not clear whether those changes would also increase the incidence of illnesses, or if we’d just see an increased range of amoeba habitat.

Now, as great as all this data is, we know what you’re really wondering: Is it safe to swim?

Generally, yes, because, as Young stated, the risk to individual swimmers is very low. However, if you’re planning to do a lot of swimming in a body of warm freshwater, and you’re concerned about your risk, there are steps you can take.

“Since the amoeba enters our body through our nasal passages, the only way to reduce exposure is to minimize the amount of water entering the nose (e.g., use of nose clips),” Young said. “For those who are swimming in warm freshwater bodies where the amoeba could be present, this would be the best way to prevent illness, but swimmers should again keep in mind that illness is still very rare, so the risk of being exposed in any given lake or other water body would be quite low.”

Also, based on cases reported globally, young males seem to be at higher risk than other demographics. “It is not clear if this is due to them being more likely to engage in swimming behaviors that increase their risk of exposure (e.g., splashing and getting water up their nose), or due to biological or other reasons,” Young said.

As the amoeba destroys healthy brain tissue and causes the life-threatening infection, symptoms include headache, fever, nausea, and vomiting, before progressing over a few days to a stiff neck, confusion, loss of balance, seizures, and even hallucinations.

Still, if you want to keep swimming without nose clips—and with zero brain-eating amoeba risk—this summer, there’s another option. “Thankfully, the amoeba cannot survive in properly disinfected and maintained swimming pools,” Young said, “so for those who are concerned about exposure, this could be another swimming alternative.”

RELATED: Triathlete’s Guide To Going From Pool To Open Water