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Primary Amebic Meningoencephalitis (PAM)

Florida Health

Disease Control

Naegleria fowleri is the causative agent for Primary Amebic Meningoencepalitis (PAM). It is a freshwater ameba commonly found in the environment worldwide. Most commonly, this ameba is found in warm bodies of fresh water, such as lakes, rivers, and hot springs, warm water discharge from industrial plants, under-chlorinated human-made aquatic venues, and soil. It has also infrequently been found in contaminated tap water and hot water heaters. Naegleria fowerli is the only species of Naegleria that has been found to infect humans. Although Naegleria fowleri is commonly found in the environment, infection occurs rarely. However, this disease has public health importance because of its high fatality rate.

Only 4 people out of 154 known infected individuals in the United States from 1962 to 2021 have survived.

Naegleria fowleri infection cannot be spread from person to person contact and will not occur as a result of drinking contaminated water.

  • Occurence
  • Transmission
  • Symptoms
  • Prevention
  • Resources and References

In the United States:

Infection with Naegleria fowleri is most common during the summer months of July, August, and September. They usually occur when it is hot for prolonged periods causing higher water temperatures, lower water levels and people tend to have increased recreational contact with fresh water. Infections have been observed to increase during heat wave years primarily in southern tier states however recent cases in Indiana, Kansas, Missouri, Minnesota, Maryland and Virginia indicate an expanding geographical area where the organism appears to be thriving.  In the United States, it has caused infections in 19 states (AR, AZ, CA, FL, GA, IN, KS, LA, MO, MD, MN, MS, NC, NM, NV, OK, SC, TX, and VA) and one territory (USVI).

In Florida:

Prior to 2008, primary amebic meningoencephalitis was not a reportable disease in Florida. However, 38 cases have been documented with Florida exposures from 1962 through 2020. Reported cases described exposures in the following counties: Baker, Brevard, Broward, Citrus, Hendry, Hillsborough, Lee, Madison, Orange, Pasco, Pinellas, Polk, Putnam, Palm Beach, Seminole, Volusia and three unknown counties. One additional case was a Florida resident who acquired the disease at a natural hot springs recreational water venue in a Central American country. All Florida cases died from the disease with the exception of a 2016 case. All but three cases were residents of Florida.

Infection with Naegleria fowleri typically occurs when the ameba enters the body through the nose. The ameba travels up the nose to the brain and spinal cord where it destroys the brain tissue causing the disease primary amebic meningoencephalitis (PAM). Generally, exposure to the ameba occurs when people use warm freshwater for vigorous activities like swimming, diving, or other rigorous activities in freshwater. Two cases of PAM in the USA have been linked to the use of household tap water for irrigation of sinuses. It is unknown why certain persons become infected with the amebe while millions of others exposed to warm recreational fresh waters do not, including those who were swimming with people who became infected.

The initial symptoms of PAM start 1 to 14 days after infection. Initial signs and symptoms of PAM include headache, fever, nausea, vomiting, and stiff neck. As the ameba causes more extensive destruction of brain tissue this leads to confusion, lack of attention to people and surroundings, loss of balance and bodily control, seizures, and hallucinations. The disease progresses rapidly and infection usually results in death within 3 to 7 days. There have been five documented instances of PAM cases surviving in North America, four in the US (FL, TX, AR and CA) and the other in Mexico. While prompt diagnosis and medical treatment may influence successful outcomes, it is unclear what specific treatment regimen is effective. Recently an investigational drug, miltefosine, has shown some promise in combination with some of other drugs. Miltefosine is commercially available for the treatment of Naegleria fowleri infections. It is important the health care clinicians inquire about fresh water exposures for patients who present with the initial signs and symptoms of PAM to assist with early detection of potential cases. If you are a clinician and have a patient with suspected Naegleria or other free-living ameba infection, please contact the CDC Emergency Operations Center at 770-488-7100 to consult with a CDC expert for diagnostic support and consultation 24/7 regarding treatment options. Additional treatment information for healthcare professionals can be found at

The only known way to prevent Naegleria fowleri infections is to refrain from water-related activities. However, some common-sense measures that might reduce risk by limiting the chance of contaminated water going up the nose include:

  • Avoid water-related activities in bodies of warm freshwater, hot springs, and thermally-polluted water such as water around power plants.
  • Avoid water-related activities in warm freshwater during periods of high water temperature and low water levels.
  • Hold the nose shut or use nose clips when taking part in water-related activities in bodies of warm freshwater such as lakes, rivers, or hot springs.
  • Avoid digging in or stirring up the sediment while taking part in water-related activities in shallow, warm freshwater areas.

Recreational water users should assume that there is always a low level of risk associated with entering all warm fresh water in southern tier states. Because the location and number of ameba in the water can vary a lot over time, posting signs is unlikely to be an effective way to prevent infections. In addition, posting signs on only some fresh water bodies might create a misconception that bodies of water that are not posted are Naegleria-free.

Information about the risks associated with Naegleria fowleri infection should be included in public health messages discussing general issues of recreational water safety and risk.

When preparing solutions of tap water for sinus irrigation the user should use tap water previously boiled for 1 minute (at elevations above 6,500 feet, boil for 3 minutes) and left to cool, or use filtered water using a filter with an absolute pore size of 1 micron or smaller, or use clearly marked distilled or sterile water in the irrigation device. 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.

CDC, Division of Parasitic Diseases – Naegleria fowleri Information

CDC Recreational Waterborne Illness Data and Information:


Other Resource Articles:

Australian Water Safety Council (2004). National Water Safety Plan 2004-07. Australian Water Safety Council, Sydney

Barnett, N. et al. (1996).  Primary Amoebic Meningoencephalitis With Naegleria fowleri:  Clinical Review.  Pediatric Neurology, 15(3), 230-234.

Boss, J. and Russel, S. (2005).  Two Fatal Cases of PAM in Tulsa County, August 2005, Oklahoma State Department of Health Epidemiology Bulletin, 37(3), 1-2.

Cabanes, P., Wallet, F., Pringuez, E., and Pernin, P. (2001).  Assessing the Risk of Primary Amoebic Meningoencephalitis from Swimming in the Presence of Environmental Naegleria fowleri.  Applied and Environmental Microbiology, 67(7), 2927-2931.

CDC - Naegleria fowleri Fact Sheet

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Culbertson, C., Ensminger, P., Overton, W. (1968).  Pathogenic Naegleria sp. – Study of a Strain Isolated from Human Cerebral Fluid.  Journal of Protozoology, 15(2), 353-363.

De Jonckheere, J. (2002). A century of Research on the Amoeboflagellate Genus Naegleria. Acta Protozoologica, 41, 309 – 342.

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Dorsch, M. (1982).  Primary Amoebic Meningoencephalitis: An Historical and Epidemiological Perspective with Particular Reference to South Australia.  South Australian Health Commision EpidemiologyBranch.

Duma, R., Ferrell, H., Nelson, E., Jones, M. (1969).  Primary Amoebic Meningoencephalitis.  The New England Journal of Medicine, 281(24), 1315-1324.

Grate, I., (2006).  Primary Amoebic Meningoencephalitis - A Silent Killer.  Canadian  Journal of Emergency Medicine, 8(5), 365-369. 

John, D. (1982).  Primary Amoebic Meningoencephalitis and the Biology of Naegleria folweri.  Annual Review of Microbiology, 36, 101-123.

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Kadlec, V., Cerva, L.,  Skvarova, J. (1978). Virulent Naegleria fowleri in an Indoor Swimming Pool, Science, 201, 1025.

Mandell, G., Bennett, J., Dolin, R. (2005).  Chapter 271:  Free-Living Amebas.  In Principals and Practice of Infectious Diseases, 6th Ed. 

Marciano-Cabral, F., Cline, M., Gaylen Bradley, S. (1987).  Specificity of Antibodies from Human Sera for Naegleria Species.  Journal of Clinical Microbiology, 25 (4), 692-697

Marciano-Cabral, F., MacLean, R., Mensah,A., and LaPat-Polasko, L. (2003). Identification of Naegleria fowleri in Domestic Water Sources by Nested PCR.  Applied and Environmental Microbiology, 60(10), 5864–5869.

Marshall, M., Naumovitz, D., Ortega, Y., Sterling, C. (1997).  Waterborne Protozoan  Pathogens.  Clinical Microbiology Review, 10(1), 67-85. 

Qvarnstrom, Y., Visvesvara, G.,  Sriram, R.,  and da Silva1,  A., (2006).  Multiplex Real-Time PCR Assay for Simultaneous Detection of Acanthamoeba spp., Balamuthia mandrillaris, and Naegleria fowleri.  Journal of Clinical Microbiology, 44(10), 3589– 3595.

Schuster, F. (1999).  Cultivation of Pathogenic and Opportunistic Free-Living Amebas. Clinical Microbiology Review, 15(30), 342-354.

Stevens,  A., Tyndall, R., Coutant, C., Willaert, E. (1977).  Isolation of the Etiological Agent of Primary Amoebic Meningoencephalitis from Artificially Heated Waters. Applied and Environmental Microbiology, 34(6), 701-705.

Thong, Y. (1982).  Chemotherapy for Primary Amoebic Meningoencephalitis.  The New England Journal of Medicine, 306, 1295-1296.

Vargas-Zepeda, J. et al. (2005).  Successful Treatment of Naegleria fowleri Meningoencephalitis by Using Intravenous Amphotericin B, Fluconazole and Rifampicin.  Archives of Medical Research, 36, 83–86.

Visvesvara, G.  (1999).  Pathogenic and opportunistic free-living amebae, p. 1383. In P. R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover, and R. H. Yolken (ed.), Manual of clinical microbiology, 7th ed. ASM Press, Washington, D. C.

Welling, F., Amuso, P., Change, S., Lewis, A. (1977).  Isolation and Identification of Pathogenic Naegleria from Florida Lakes.  Applied and Environmental Microbiology, 34 (6), 661-667.

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Yoder, J., Straif_Bourgeois, S., Roy, S., et al. (2012).  Primary Amebic Meningoencephalitis Deaths Associated With Sinus Irrigation Using Contaminated Tap Water. Clinical Infectious doi: 10.1093/cid/cis626 First published online: August 22, 2012

Yoder JS, Eddy BA, Visvesvara GS, Capewell L, Beach MJ. (2010). The Epidemiology of Primary Amoebic Meningoencephalitis in the USA, 1962-2008.  Epidemiol Infect. Jul;138(7):968-75.  Epub 2009 Oct 22.  Located at

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