According to the CDC, Naegleria fowleri is an amoeba commonly found in freshwater, such as lakes, rivers, and hot springs.

The amoeba infects people when contaminated water enters the body through the nose. It then travels to the brain, where it destroys brain tissue, causing swelling and death. Infection is not possible from drinking water contaminated with Naegleria, nor is person-to-person transmission possible. Furthermore, it has not been shown to spread via water vapor or aerosol droplets (such as shower mist or vapor from a humidifier).

Symptoms of infection are similar to those caused by other more common illnesses, such as bacterial meningitis.

According to the CDC, Naegleria fowleri causes the disease primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue.

Initial symptoms of PAM start about 5 days (range 1 to 9 days) after infection. The initial symptoms may include headache, fever, nausea, or vomiting. Later symptoms can include stiff neck, confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. After the start of symptoms, the disease progresses rapidly and usually causes death within about 5 days (range 1 to 12 days).

The fatality rate following infection is exceptionally high, at over 97%. Only 4 people out of 148 known infected individuals in the United States from 1962 to 2019 have survived.

While the amoeba itself is common, human infections are highly rare. From 2010 to 2019, 34 infections were reported within the U.S. Of those cases, 30 people were infected by recreational water, three people were infected after performing nasal irrigation using contaminated tap water, and one person was infected by contaminated tap water used on a backyard slip-n-slide.

More recently, 3-year-old Bakari Williams died after he was infected with the amoeba at a Texas splashpad in early September, 2021. And in September, 2020, 6-year-old Josiah McIntyre died from infection of the amoeba, which may also have occurred at a Texas splashpad. While two positive tests for the amoeba were found in a civic center water source as well as a fire hydrant, the location of exactly where McIntyre’s transmission occurred was never determined.

The CDC says people cannot get Naegleria fowleri infection from a properly cleaned, maintained, and disinfected swimming pool.