Primary Amebic Meningoencephalitis FAQs

Primary Amebic Meningoencephalitis, or PAM, is an infection of the brain and the membranous tissues that surround and cover the spinal cord and brain. The causative agent is an ameba (single-celled organism) called Naegleria fowleri. In very rare situations, Naegleria fowleri has been known to cause infection in humans. The infection progresses rapidly, causing massive destruction of the brain and meningeal tissues, resulting in coma and death usually within 10 days from onset of symptoms. This infection is almost always fatal.

Naegleria fowleri is commonly found around the world.  In the U.S., 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
• 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.
• Soil

Naegleria fowleri is not found in salt water, like the ocean.

You cannot be infected with Naegleria fowleri by drinking contaminated water.

Naegleria fowleri infects people by entering the body through the nose. Generally, this occurs when people swim or dive in warm freshwater, especially stagnant ponds or lakes in warm climate areas. The ameba travels up the nose to the brain and spinal cord where it destroys brain tissue. The ameba may also enter the nose when nasal irrigation or sinus flushes are performed using plain tap water rather than sterile, distilled, or lukewarm previously boiled water.

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 fatality rate is over 97%. Only 4 people out of 143 known infected individuals in the United States from 1962 to 2016 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. Please go to the CDC website for up-to-date information on available treatments and their effectiveness.

No. It can take weeks to grow and 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 such as Texas.

The risk of Naegleria fowleri infection is very low. There have been 40 reported infections in the U.S. in the 10 years from 2007 to 2016, 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.

Just like the U.S., the risk of Naegleria fowleri infections is very rare in Texas. Cases that occur in the U.S. typically happen in states with warm climate and abundance of recreational waters such as Texas. From 1983 to 2012 there were 28 deaths from Naegleria fowleri infections in Texas.

Compared to other conditions such as drowning and other types of meningitis, PAM is very rare. In Texas, from 2004 to 2008, there were 3 cases of PAM, 749 deaths from drowning, and 225 cases of bacterial meningitis.

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:

• Sinus Rinsing For Health or Religious Practice
• Ritual Nasal Rinsing & Ablution
• Public Drinking Water Systems

Portions of these FAQs were developed by Naegleria workgroup sponsored by the Council or State and Territorial Epidemiologists and CDC.

For further information on protecting yourself from recreational water illnesses, go to http://www.cdc.gov/healthyswimming/.