Naegleria fowleri infections are extraordinarily rare. Between 1962 and 2024, only 167 cases were reported in the entire United States, and fewer than 10 people are infected in a typical year. Globally, roughly 488 cases have been documented since 1962, with the highest numbers in the US, Pakistan, and Australia. To put that in perspective, tens of millions of Americans swim in warm freshwater every summer, and the odds of any individual contracting the infection are vanishingly small.
How the Numbers Break Down
Over more than six decades of tracking, the US has averaged roughly 2 to 3 cases per year. The infection rate has stayed relatively stable over time, meaning it hasn’t become more common despite growing awareness and better surveillance. The CDC classifies it as one of the rarest infectious diseases in the country.
That rarity, however, comes with a grim tradeoff: the infection is almost universally fatal. Only four people in the United States are known to have survived. Symptoms typically begin about five days after exposure, and death usually follows within another five days. Many cases are only confirmed after the patient has already died, partly because the early symptoms (fever, headache, stiff neck, nausea) look identical to bacterial meningitis.
Where the Amoeba Lives
Naegleria fowleri is a single-celled organism found naturally in warm freshwater and soil around the world. It thrives at temperatures around 25°C (77°F) and can tolerate even warmer water, which is why infections cluster in southern states during the hottest months of the year. Lakes, ponds, rivers, hot springs, and poorly maintained swimming pools are the primary sources. The amoeba does not survive well in saltwater.
Infection happens only when contaminated water is forced up the nose, allowing the organism to travel along the olfactory nerve into the brain. You cannot get infected by swallowing contaminated water or by being near someone who is infected. This narrow route of entry is one reason the infection is so rare despite the amoeba being widespread in the environment.
Cases Are Shifting Northward
While the total number of infections hasn’t increased, the geographic range has. A CDC analysis of cases from 1978 to 2018 found that exposure locations shifted northward by about 13.3 kilometers per year. Five of six Midwestern cases occurred after 2010, in states like Minnesota, Indiana, and Kansas. Rising water temperatures tied to climate change are the likely driver, expanding the zones where the amoeba can flourish in summer.
This doesn’t mean the infection is becoming common in northern states. It means the already tiny risk now extends to areas where it was previously almost nonexistent.
Who Gets Infected
The CDC has historically reported a median patient age of 11, reflecting the fact that children and teenagers are more likely to jump, dive, and roughhouse in warm lakes. But a recent retrospective analysis of 22 cases found a broader age range than expected, with 32% of patients between 51 and 79 years old. About 77% of patients were male, consistent with the idea that the infection is linked to vigorous water activities that force water up the nose.
Not Just Swimming
Most cases involve recreational swimming, but a small number of infections have been traced to tap water used for nasal rinsing. In 2011, two people in Louisiana died after using neti pots filled with unboiled tap water. These were the first US cases linked to treated municipal water supplies. The amoeba had survived in household plumbing, and the brief contact time during sinus irrigation wasn’t enough to kill it.
Cases tied to religious ablution (ritual washing that involves directing water into the nose) have also been documented in Pakistan and Australia. If you use a neti pot or any nasal rinse device, using distilled, sterile, or previously boiled water eliminates this risk entirely.
Why It’s So Hard to Diagnose
Part of what makes Naegleria fowleri so deadly is that doctors rarely see it. Early symptoms are indistinguishable from bacterial meningitis: sudden severe headache, fever, nausea, and a stiff neck. Because the infection is so uncommon, it’s often not considered until it’s too late. Lab tests can detect the amoeba in spinal fluid, but those tests have to be specifically requested. The disease progresses so rapidly that the window for effective treatment is extremely narrow.
Reducing an Already Tiny Risk
The CDC recommends holding your nose shut or wearing a nose clip when jumping or diving into warm freshwater. In hot springs and naturally heated water, keeping your head above the surface is the simplest precaution. Avoiding water activities in shallow, warm, stagnant bodies of water during heat waves further reduces exposure. For nasal irrigation, always use water that has been boiled for at least one minute and cooled, or use distilled or sterile water.
These steps aren’t about managing a common threat. They’re simple habits that effectively neutralize a risk that, while extremely remote, carries catastrophic consequences on the rare occasion it does occur.