General Information
Frequently asked questions about Naegleria fowleri, commonly known as the “brain-eating ameba”
- What is Naegleria?
- How does Naegleria fowleri infect people?
- Where is Naegleria fowleri found?
- In what water temperature does Naegleria fowleri cause infection?
- What is the source of food for Naegleria fowleri?
- Can I get a Naegleria fowleri infection from a properly disinfected swimming pool?
- How common are Naegleria fowleri infections in the United States?
- When do Naegleria fowleri infections most commonly happen?
- Can infection be spread from one person to another?
- What are the symptoms of Naegleria fowleri infection?
- What is the cause of death from Naegleria fowleri infection?
- What is the death rate for an infected person who begins to show signs and symptoms?
- Is there effective treatment for infection with Naegleria fowleri?
- What should I do if I have been swimming or playing in fresh water and think I have symptoms of PAM?
- How common is Naegleria fowleri in the environment?
- Will Naegleria fowleri infections become more common because of climate change?
- Is there a routine and rapid test for Naegleria fowleri in the water?
- How does the risk of Naegleria fowleri infection compare with other water-related risks?
- What swimming behaviors have been associated with Naegleria fowleri infection?
- How will the public know if a lake or other water body has Naegleria fowleri?
- How can I prevent infection with Naegleria fowleri?
What is Naegleria?
Naegleria is a free-living ameba (a single-celled living organism). It is so small that it can only be seen with a microscope. It is commonly found in warm fresh water (such as lakes, rivers, and hot springs) and soil. Only one species of Naegleria infects people: Naegleria fowleri.
How does Naegleria fowleri infect people?
Naegleria fowleri infects people when water containing the ameba enters the body through the nose. This typically happens when people go swimming, diving, or when they put their heads under fresh water, like in lakes and rivers. The ameba then travels up the nose to the brain, where it destroys the brain tissue and causes a devastating infection called primary amebic meningoencephalitis (PAM). PAM is almost always fatal.
Naegleria fowleri infections may also happen when people use contaminated tap water to cleanse their noses during religious practices or rinse their sinuses (sending water up the nose).
In very rare instances, people have gotten Naegleria fowleri infections from recreational water that didn’t have enough chlorine in it, such as pools, splash pads, or surf parks.
There is no evidence that Naegleria fowleri can spread through water vapor or aerosol droplets (such as shower mist or vapor from a humidifier).
People cannot be infected with Naegleria fowleri by drinking contaminated water.
Where is Naegleria fowleri found?
Naegleria fowleri lives in warm fresh water and soil around the world. The amebae may be present in any freshwater body in the United States, regardless of the state, especially during the warmer months of July, August, and September.
Naegleria fowleri is a heat-loving (thermophilic) organism, meaning it thrives in heat and likes warm water. It grows best at high temperatures up to 115°F (46°C) and can survive for short periods at even higher temperatures. Scientists have tested water temperatures from lakes and rivers linked to some PAM cases, and the temperatures have typically been higher than 80°F. However, it is possible that the amebae may live in water with a temperature below 80°F.
The ameba can be found in:
- Warm fresh water, such as lakes and rivers
- Geothermal (naturally hot) water, such as hot springs
- Warm water discharge from industrial or power plants
- Untreated geothermal (naturally hot) drinking water sources
- Swimming pools, splash pads, surf parks, or other recreational venues that are poorly maintained or don’t have enough chlorine in them
- Tap water
- Water heaters
- Soil, including sediment at the bottom of lakes, ponds, and rivers
Naegleria fowleri is not found in salt water, like the ocean.
In what water temperature does Naegleria fowleri cause infection?
Naegleria fowleri is a heat-loving (thermophilic) organism, meaning it thrives in heat and likes warm water. It grows best at high temperatures up to 115°F (46°C) and can survive for short periods at even higher temperatures. Scientists have tested water temperatures from lakes and rivers linked to some PAM cases, and these temperatures have typically been higher than 80°F. However, it is possible that the amebae may live in water with a temperature below 80°F. It is less likely to be found in the water as temperatures decline. But the ameba can be found in lake or river sediment at temperatures well below where one would find the ameba in the water.
Can I get a Naegleria fowleri infection from a properly disinfected swimming pool?
No. You cannot get a Naegleria fowleri infection from a properly cleaned, maintained, and disinfected swimming pool.
In very rare instances, Naegleria fowleri has been found in swimming pools, splash pads, surf parks, or other recreational venues that are poorly maintained or don’t have enough chlorine in them.
How common are Naegleria fowleri infections in the United States?
Naegleria fowleri infections are rare.* In the United States, between zero and five cases were diagnosed annually from 2013 to 2022. During this period, a total of 29 infections were reported in the United States.
Most Naegleria fowleri infections happen in young males, especially those 14 years old and younger. The reasons for this aren’t clear. It’s possible that young boys are more likely than others to participate in activities such as diving into the water and playing in the sediment at the bottom of lakes and rivers.
*Rare Disease
There is no universal definition of a “rare disease,” but the U.S. Rare Disease Act of 2002 defined a rare disease as a disease that affects fewer than 200,000 people in the United States. This definition has been adopted by the National Institutes of Health, Genetic and Rare Diseases Information Centers.
When do Naegleria fowleri infections most commonly happen?
Infections usually happen when temperatures are hot, which results in higher water temperatures and lower water levels.
While infections with Naegleria fowleri are rare, they happen mainly during the summer months of July, August, and September.
What are the symptoms of Naegleria fowleri infection?
Naegleria fowleri causes PAM, a brain infection that destroys brain tissue. In its early stages, symptoms of PAM may be similar to symptoms of bacterial meningitis.
The first symptoms of PAM usually start about 5 days after infection, but they can start within 1 to 12 days. Symptoms may include headache, fever, nausea, or vomiting. Later symptoms can include stiff neck, confusion, lack of attention to people and surroundings, seizures, hallucinations, and coma. After symptoms start, the disease progresses rapidly and usually causes death within about 5 days (but death can happen within 1 to 18 days).
Is there effective treatment for infection with Naegleria fowleri?
Because PAM is so rare, and because the infection progresses so quickly, effective treatments have been challenging to identify. There is some evidence that certain drugs may be effective, but we are still learning about the best drugs to treat these infections. Currently, PAM is treated with a combination of drugs, often including amphotericin B, azithromycin, fluconazole, rifampin, miltefosine, and dexamethasone. These drugs are used because they are thought to be effective against Naegleria fowleri and have been used to treat patients who survived. Miltefosine is the newest of these drugs. It has been shown to kill Naegleria fowleri in the laboratory and has been used to treat three survivors.
What should I do if I have been swimming or playing in fresh water and think I have symptoms of PAM?
Infection with PAM is rare. The early symptoms of PAM 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, vomiting, or stiff neck, particularly if they have been in warm fresh water recently.
How common is Naegleria fowleri in the environment?
Naegleria fowleri occurs naturally in freshwater bodies, such as lakes, rivers, and hot springs, and in soil. The amebae are more likely to live in sediment at the bottom of lakes, ponds, and rivers, so people should avoid digging in, or stirring up the sediment in shallow, warm fresh water. Though the risk is low, people should always assume there is a risk for infection whenever entering warm fresh water.
In the United States, most infections have been linked to swimming in southern states, like Florida and Texas. However, the geographical areas where Naegleria fowleri infections happen in the United States are changing. Evidence suggests that the range of Naegleria fowleri is expanding northward, which is possibly a result of climate change and warmer temperatures.
In very rare instances, Naegleria fowleri has been found in swimming pools, splash pads, surf parks, or other recreational venues that are poorly maintained or don’t have enough chlorine in them.
Will Naegleria fowleri infections become more common because of climate change?
It is possible that Naegleria fowleri infections will become more common because of climate change. This heat-loving ameba thrives in warm fresh water such as lakes, rivers, and hot springs. Most infections in the United States have happened in southern states, but cases have been reported in more northern states in recent years. Climate change may be a contributing factor. As air temperatures rise, water temperatures in lakes and ponds also rise and water levels may be lower. These conditions provide a more favorable environment for the ameba to grow. Heat waves, when air and water temperatures may be higher than usual, may also allow the amebae to thrive.
Since 2010, cases have been confirmed in more northern states such as Nebraska, Iowa, Minnesota, Indiana, Maryland, and northern California, which suggests a northward expansion of cases.
Naegleria fowleri may be present in any freshwater body in the United States, regardless of the state, especially during the warmer months of July, August, and September.
Is there a routine and rapid test for Naegleria fowleri in the water?
No. It can take weeks to perform an environmental investigation and identify the ameba in water. Previous water testing has shown that Naegleria fowleri is commonly found in freshwater bodies. Though the risk is low, recreational water users should always assume there is a risk for infection whenever entering warm fresh water.
How does the risk of Naegleria fowleri infection compare with other water-related risks?
The risk of Naegleria fowleri infection is very low. There were 29 reported infections in the United States in the 10 years from 2013 to 2022, despite millions of recreational water exposures each year. By comparison, in the 10 years from 2011 to 2020, there were an estimated 4,012 unintentional drowning deaths each year in the United States.
What swimming behaviors have been associated with Naegleria fowleri infection?
Behaviors associated with the infection include diving or jumping into the water, putting the head under water, or engaging in other activities that cause water to go up the nose. Since the amebae are more likely to live in the sediment at the bottom of lakes, ponds, or rivers, swimmers should also avoid digging or stirring up the sediment.
Most Naegleria fowleri infections happen in young males, especially those 14 years old and younger. The reasons for this aren’t clear. It’s possible that young boys are more likely to participate in activities such as diving into the water and playing in the sediment at the bottom of lakes and rivers.
How will the public know if a lake or other water body has Naegleria fowleri?
Naegleria fowleri is naturally occurring in fresh water. People should always assume that Naegleria fowleri is present in warm freshwater lakes, rivers, and hot springs 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 commonly occurs in water, but infections are rare.
- The relationship between finding Naegleria fowleri in the water and people getting infected 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 measure the amount of Naegleria fowleri in water.
- Posting signs might create misconceptions:
- People might think that a body of water without signs is free from Naegleria fowleri.
- People might think that if a sign is posted near one part of a water body, other parts without signs are free of Naegleria fowleri.
How can I prevent infection with Naegleria fowleri?
Naegleria fowleri infects people when water containing the ameba enters the body through the nose. Infection is rare and typically happens when people go swimming, diving, or put their heads under water in warm freshwater places, like lakes and rivers. Very rarely, infections have been reported when people cleanse their noses during religious practices or rinse their sinuses (nose) using contaminated tap 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 preventing water from going up the nose. 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 talking to a health care provider. If you have any questions about the amebae described above or think that you may be infected, talk to a health care provider immediately.