You get a brain-eating amoeba infection when contaminated warm freshwater is forced up your nose. The organism, called Naegleria fowleri, travels from the nasal passages along the olfactory nerve and into the brain, where it causes a rapid and almost always fatal infection called primary amebic meningoencephalitis (PAM). You cannot get infected by swallowing contaminated water. The only route is through the nose.
How the Amoeba Enters Your Brain
Naegleria fowleri is a single-celled organism that lives in warm freshwater and soil worldwide. When water containing the amoeba gets pushed into your nasal cavity, whether from diving, jumping, or dunking your head, the organism attaches to the tissue lining your nose. From there, it migrates along the nerve responsible for your sense of smell, passing through the thin bone at the top of the nasal cavity and directly into the brain.
Once inside the brain, the amoeba feeds on brain tissue, triggering massive inflammation. This is why swallowing the same water is harmless: stomach acid destroys the organism, and the digestive tract offers no pathway to the brain. The nasal route is the only one that works.
Where Naegleria Fowleri Lives
The amoeba thrives in warm freshwater. Lakes, rivers, ponds, and hot springs are its primary habitats, especially during prolonged hot weather when water temperatures rise and water levels drop. It’s more concentrated in shallow water and in the sediment at the bottom of lakes and ponds, which is why disturbing mud or sand in shallow areas increases the risk.
Naegleria fowleri has historically been concentrated in the southern United States and Central America, but cases have begun appearing in northern states. Researchers at the Ohio Journal of Public Health have flagged this northward expansion as a likely consequence of climate change, with warmer summers creating hospitable conditions in regions where PAM was previously undocumented.
Activities That Cause Infection
Most infections happen during recreational swimming in warm freshwater. Jumping or diving into a lake, river, or pond forces water up the nose with enough pressure to deliver the amoeba deep into the nasal passages. Children and young adults are disproportionately affected, likely because they spend more time in the water and are more likely to engage in activities that force water into the nose.
But swimming isn’t the only risk. Infections have also been linked to:
- Sinus rinses with tap water. Using a neti pot or squeeze bottle filled with unsterilized tap water can introduce the amoeba directly into your nasal passages. The CDC recommends using only boiled, distilled, or sterile water for any nasal rinsing.
- Household plumbing. Naegleria fowleri can live in the biofilm that coats the inside of water pipes. When a water utility raises disinfectant levels, pieces of that biofilm can break loose and come through your tap. Running taps and showerheads for five minutes before use helps flush the pipes.
- Hoses and sprinklers. Children playing with garden hoses or sprinklers can accidentally squirt water up their noses. The CDC specifically warns against unsupervised play with hoses for this reason.
Why It’s So Dangerous
PAM progresses with terrifying speed. The first symptoms typically appear about 5 days after exposure, though the window ranges from 1 to 12 days. Early signs look like many other illnesses: headache, fever, nausea, and vomiting. This resemblance to common infections like bacterial meningitis or the flu is one reason PAM is frequently misdiagnosed in its critical early hours.
Within days, the infection advances to stiff neck, confusion, seizures, hallucinations, and coma. Death typically occurs about 5 days after symptoms first appear, though it can happen anywhere from 1 to 18 days after onset. The fatality rate is greater than 97 percent. Worldwide, only a handful of people have survived.
The rarity of the infection is worth noting alongside its severity. Only a few cases are reported in the United States each year, despite millions of people swimming in warm freshwater. The infection is extraordinarily deadly but also extraordinarily uncommon.
How to Reduce Your Risk
You can’t make warm freshwater completely safe from Naegleria fowleri, but you can keep it out of your nose. Hold your nose shut or wear a nose clip when jumping or diving into freshwater lakes, rivers, or ponds. Avoid putting your head underwater in hot springs and naturally heated bodies of water. Stay out of shallow, warm, stagnant water, especially during heat waves, and don’t dig into or kick up sediment on the bottom.
At home, never use tap water for sinus rinses. Boil water for at least one minute and let it cool, or use distilled or sterile water labeled for that purpose. If your water utility has issued a notice about raised disinfectant levels, run your bath, shower, and faucet taps for five minutes before use to clear any loosened biofilm from the pipes. Keep water out of children’s noses during baths, and supervise any play involving hoses or sprinklers.
Properly chlorinated swimming pools and water parks are not a risk. The amoeba cannot survive in adequately treated water. Saltwater and ocean water are also safe, as Naegleria fowleri requires freshwater to survive.