Naegleria and Amebic Meningoencephalitis

Naegleria fowleri is a free-living ameba commonly found in warm freshwater. It can cause a rare but severe brain infection called primary amebic meningoencephalitis. Most infections are fatal. People become infected with Naegleria fowleri when contaminated water enters the body through the nose. Infection typically occurs when people go swimming or diving in warm freshwater, such as lakes or rivers.

What is Naegleria?


How does infection with Naegleria occur?

Naegleria infects people by entering the body through the nose. Generally, this occurs when people use warm freshwater for activities like swimming or diving. The ameba travels up the nose to the brain and spinal cord where it destroys the brain tissue. Infections do not occur as a result of drinking contaminated water.

Where is Naegleria found?

Naegleria fowleri is found around the world. In the United States, it has caused infections in 16 states including MN. The ameba grows best in warm or hot water. Most commonly, the ameba may be found in:

  • Bodies of warm freshwater, such as lakes, rivers
  • Geothermal (naturally hot) water such as hot springs
  • Geothermal (naturally hot) drinking water sources
  • Warm water discharge from industrial plants
  • Poorly maintained and minimally-chlorinated or unchlorinated swimming pools
  • Soil
  • Naegleria is not found in salt water locations like the ocean.

Can I get Naegleria infection from a disinfected swimming pool?

No. You cannot get a Naegleria infection from a properly cleaned, maintained, and disinfected swimming pool.

How common are Naegleria infections in the United States?

Infections are very rare even though Naegleria is commonly found in freshwater. In the 10 years from 2002 to 2011, 32 infections were reported in the U.S. Of those cases, 28 people were infected by contaminated recreational water, 2 people were infected by water from a contaminated, geothermal (naturally hot), untreated drinking water supply, and 2 people were infected after performing nasal irrigation using contaminated tap water.

When do Naegleria infections most commonly occur?

While infections with Naegleria are very rare, they occur mainly during the summer months of July, August, and September. These infections are more likely to occur in southern tier states, but can also occur in other locations. They usually occur when it is hot for prolonged periods causing higher water temperatures and lower water levels. Infections can increase during heat wave years.

Can infection be spread from one person to another?

No. Naegleria infection cannot be spread from one person to another.

What are the symptoms of Naegleria infection?

Infection with Naegleria causes the disease amebic meningoencephalitis also known as primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue. In its early stages, Naegleria infection may be similar to bacterial meningitis.

Initial symptoms of PAM start about 5 days (range, 1 to 7 days) after infection. The initial symptoms include headache, fever, nausea, vomiting, and stiff neck. Later symptoms include 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 5 days (range, 1 to 12 days).

Is there effective treatment for infection with Naegleria?

It is not clear. Several drugs are effective against Naegleria in the laboratory. However, their effectiveness is unclear since almost all infections have been fatal even when people were treated.


Infection with Naegleria is very rare. The early symptoms of Naegleria infection are more likely to be caused by other more common illnesses, such as 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 fresh water within the previous 2 weeks.

How common is Naegleria in the environment?

Naegleria is commonly found in warm lakes during the summer. 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 and can survive for short periods of time at higher temperatures.

Is there a routine and rapid test for Naegleria in the water?

No. It can take weeks to identify the ameba. Newer genetic detection tests for ameba are still under development. Water testing suggests that the amebae are so common that recreational water users should assume that there is a low level of risk when entering warm fresh water.


Although the infections are severe, the risk of Naegleria fowleri infection is very low. There have been 32 reported infections in the U.S. during the 10 years from 2002 to 2011, despite millions of recreational water exposures each year. By comparison, during the ten years from 1996 to 2005, there were over 36,000 drowning deaths in the U.S.


Recreational water users should assume that there is always a low level of risk whenever they enter warm freshwater (for example swimming, waterskiing). 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 are Naegleria fowleri-free.

How can I reduce the risk of infection with Naegleria?

Naegleria is found in many warm freshwater lakes and rivers in the United States. It is likely that a low risk of Naegleria infection will always exist with recreational use of warm freshwater lakes, rivers, and hot springs. The low number of infections makes it difficult to know why some people have been infected compared to the millions of other people using the same or similar waters across the U.S. The only known way to prevent Naegleria infections is to refrain from water-related activities.


Swimming-related risk



Non-swimming-related risk

Even more rarely, infections have been reported when people submerge their heads, cleanse during religious practices, or irrigate their sinuses (nose) using heated and contaminated tap water. If you are making a solution for irrigating, flushing, or rinsing your sinuses (for example, by using a neti pot, sinus rinse bottle or other irrigation device), use water that has been:

  • Purchased with a label specifying that it contains distilled or sterile water

Rinse the irrigation device after each use with water that has been previously boiled, filtered, distilled, or sterilized and leave the device open to air dry completely.

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Updated Monday, August 12, 2013 at 11:40AM