Primary amebic meningoencephalitis (PAM) is a very rare form of parasitic meningitis that causes a brain infection that is usually fatal. PAM is caused by the microscopic ameba (a single-celled living organism) Naegleria fowleri when water containing the ameba enters the body through the nose.
Naegleria fowleri is found around the world. In the United States, the majority of infections have been linked to swimming in warm freshwater located in southern-tier states, like Florida and Texas.1 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
- Untreated 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.2, 3
Naegleria fowleri is not found in salt water, like the ocean.
Naegleria fowleri infects people by entering the body through the nose. This typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers.1 The Naegleria fowleri ameba 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 practices4, 5, and when people irrigate their sinuses (nose) using contaminated tap water6.
Naegleria fowleri infections are rare. In the 10 years from 2006 to 2015, 37 infections were reported in the United States and there were two survivors.
PAM 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 are similar to symptoms of bacterial meningitis.
Initial symptoms of PAM start 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 about 5 days (range 1 to 12 days).
PAM is rare, with no more than 8 cases reported each year in the United States. The early symptoms of PAM are more likely to be caused by other more common illnesses, such as bacterial or viral 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.
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.
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, 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:
- Yoder JS, Eddy BA, Visvesvara GS, Capewell L, Beach MJ. The epidemiology of primary amoebic meningoencephalitis in the USA, 1962-2008. Epidemiol Infect. 2010;138:968-75.
- Griffin JL. Temperature tolerance of pathogenic and nonpathogenic free-living amoebas. Science. 1972;178(63):869-70.
- Stevens AR, Tyndall RL, Coutant CC, Willaert E. Isolation of the Etiological Agent of Primary Amoebic Meningoencephalitis from Artificially Heated Waters. Appl Environ Microbiol. 1977;34(6):701-705.
- CDC. Primary amebic meningoencephalitis associated with ritual nasal rinsing — St. Thomas, U.S. Virgin Islands, 2012. MMWR Morb Mortal Wkly Rep. 2013;62(45):903.
- Shakoor S, Beg MA, Mahmood SF, Bandea R, Sriram R, Noman F, et al. Primary amebic meningoencephalitis caused by Naegleria fowleri, Karachi, Pakistan.[PDF – 4 pages] Emerg Infect Dis. 2011:17;258-61.
- Yoder JS, Straif-Bourgeois S, Roy SL, Moore TA, Visvesvara GS, Ratard RC, Hill V, Wilson JD, Linscott AJ, Crager R, Kozak NA, Sriram R, Narayanan J, Mull B, Kahler AM, Schneeberger C, da Silva AJ, Beach MJ. Deaths from Naegleria fowleri associated with sinus irrigation with tap water: a review of the changing epidemiology of primary amebic meningoencephalitis. Clin Infect Dis. 2012;1-7.
- Page last reviewed: April 15, 2016
- Page last updated: April 15, 2016
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