Frequently Asked Questions
Naegleria is an ameba (single-celled living organism) commonly found in warm freshwater (for example, lakes, rivers, and hot springs) and soil. Only one species (type) of Naegleria infects people: Naegleria fowleri.
Naegleria fowleri infects people when water containing the ameba enters the body through the nose. This typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. The Naegleria fowleri ameba then travels up the nose to the brain where it destroys the brain tissue.
You cannot be infected with Naegleria fowleri by drinking contaminated water. In very rare instances, Naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or contaminated tap water) enters the nose, for example when people submerge their heads or cleanse their noses during religious practices, and when people irrigate their sinuses (nose) using contaminated tap water. Naegleria fowleri has not been shown to spread via water vapor or aerosol droplets (such as shower mist or vapor from a humidifier).
Naegleria fowleri is found around the world. In the United States, the majority of infections have been caused by Naegleria fowleri from freshwater located in southern-tier states. The ameba can be found in:
- Bodies of warm freshwater, such as lakes and rivers
- Geothermal (naturally hot) water, such as hot springs
- Warm water discharge from industrial plants
- Geothermal (naturally hot) drinking water sources
- Swimming pools that are poorly maintained, minimally-chlorinated, and/or un-chlorinated
- Water heaters. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C) and can survive for short periods at higher temperatures.
Naegleria fowleri is not found in salt water, like the ocean.
Naegleria fowleri is a heat-loving (thermophilic) organism. It grows best at higher temperatures up to 115°F (46°C) and can survive for short periods at higher temperatures. It is less likely to be found in the water as temperatures decline. The ameba can be found in lake or river sediment at temperatures well below where one would find the ameba in the water.
Naegleria fowleri eats other organisms like bacteria found in the sediment in lakes and rivers.
No. You cannot get a Naegleria fowleri infection from a properly cleaned, maintained, and disinfected swimming pool.
Naegleria fowleri infections are rare*. In the ten years from 2011 to 2020, 33 infections were reported in the U.S. Of those cases, 29 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.
There is no universal definition of a “rare disease” but the U.S. Rare Disease Act of 2002external icon defined a rare disease as affecting less than 200,000 people in the U.S. and this definition has been adopted by the National Institutes of Health, Genetic and Rare Diseases Information Centers.external icon
While infections with Naegleria fowleri are rare, they occur mainly during the summer months of July, August, and September. Infections are more likely to occur in southern-tier states, but can also occur in other more northern states. Infections usually occur when it is hot for prolonged periods of time, which results in higher water temperatures and lower water levels.
No. Naegleria fowleri infection cannot be spread from one person to another.
Naegleria fowleri causes the disease primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue. In its early stages, symptoms of PAM may be similar to symptoms of bacterial meningitis.
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 infection destroys brain tissue causing brain swelling and death.
The fatality rate is over 97%. Only four people out of 151 known infected individuals in the United States from 1962 to 2020 have survived.
It is not clear. Several drugs are effective against Naegleria fowleri in the laboratory. However, their effectiveness is unclear since almost all infections have been fatal, even when people were treated with similar drug combinations. Recently, two people with Naegleria infection survived after being treated with a new drug called miltefosine that was given along with other drugs and aggressive management of brain swelling.
Infection with Naegleria fowleri is rare. The early symptoms of Naegleria fowleri infection are similar to those caused by other more common illnesses, such as bacterial meningitis . People should seek medical care immediately whenever they develop a sudden onset of fever, headache, stiff neck, and vomiting, particularly if they have been in warm freshwater recently.
Naegleria fowleri is commonly found in lakes in southern-tier states during the summer but more recently has caused infections in northern states. This means that recreational water users should be aware that there will always be a low level risk of infection when entering these waters. In very rare instances, Naegleria has been identified in water from other sources such as inadequately chlorinated swimming pool water or heated and contaminated tap water. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C) and can survive for short periods at higher temperatures.
No. It can take weeks to identify the ameba, but new detection tests are under development. Previous water testing has shown that Naegleria fowleri is commonly found in freshwater venues. Therefore, recreational water users should assume that there is a low level of risk when entering all warm freshwater, particularly in southern-tier states.
The risk of Naegleria fowleri infection is very low. There have been 33 reported infections in the U.S. in the ten years from 2011 to 2020, despite millions of recreational water exposures each year. By comparison, in the ten years from 2001 to 2010, there were more than 34,000 drowning deaths in the U.S.
Behaviors associated with the infection include diving or jumping into the water, submerging the head under water or engaging in other water-related activities that cause water to go up the nose.
Recreational water users should assume that Naegleria fowleri is present in warm freshwater across the United States. Posting signs based on finding Naegleria fowleri in the water is unlikely to be an effective way to prevent infections. This is because:
- Naegleria fowleri occurrence is common, infections are rare.
- The relationship between finding Naegleria fowleri in the water and the occurrence of infections is unclear.
- The location and number of amebae in the water can vary over time within the same lake or river.
- There are no rapid, standardized testing methods to detect and quantitate Naegleria fowleri in water.
- Posting signs might create a misconception that bodies of water without signs or non-posted areas within a posted water body are Naegleria fowleri-free.
Naegleria fowleri infects people when water containing the ameba enters the body through the nose. Infection is rare and typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. Very rarely, infections have been reported when people submerge their heads or get water up their nose, cleanse their noses during religious practices, or irrigate their sinuses (nose) using contaminated tap or faucet water. Naegleria fowleri can grow in pipes, hot water heaters, and water systems, including treated public drinking water systems.
Personal actions to reduce the risk of Naegleria fowleri infection should focus on limiting the amount of water going up the nose and lowering the chances that Naegleria fowleri may be in the water.
Please visit the following pages for information on lowering your risk of infection in specific situations:
This information is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the parasites described above or think that you may have a parasitic infection, consult a health care provider.