Prevention & Control
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 put their heads fully underwater, 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. You cannot get infected from drinking water contaminated with Naegleria. You can only be infected when contaminated water goes up into your nose.
Risk of Infection
Naegleria fowleri is found naturally in freshwater lakes, rivers, and hot springs in the United States1-3,, particularly in southern-tier states4-8, but has caused infections as far north as Minnesota9. No data exist to accurately estimate the true risk of PAM. Hundreds of millions of visits to swimming venues occur each year in the United States10 that result in 0-8 infections per year 11. It is unknown why certain people become infected with the amebae while millions of others exposed to warm recreational fresh waters do not, including those who were swimming with people who became infected.
Attempts have been made to determine what concentration of Naegleria fowleri in the environment poses an unacceptable risk12. However, no method currently exists that accurately and reproducibly measures the numbers of amebae in the water. This makes it unclear how a standard might be set to protect human health and how public health officials would measure and enforce such a standard. However, the risk of Naegleria fowleri infection is very low. There have been 29 reported infections in the United States in the 10 years from 2013 to 2022, despite hundreds of millions of recreational water exposures each year10. 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.
- Visvesvara GS. Free-living amebae as opportunistic agents of human disease. J Neuroparasitol. 2010;1.
- Visvesvara GS, Moura H, Schuster FL. Pathogenic and opportunistic free-living amoebae: Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri, and Sappinia diploidea. FEMS Immunol Med Microbiol. 2007;50:1-26.
- Marciano-Cabral F, Cabral G. The immune response to Naegleria fowleri amebae and pathogenesis of infection. FEMS Immunol Med Microbiol. 2007;51:243-59.
- Maclean RC, Richardson DJ, LePardo R, Marciano-Cabral F. The identification of Naegleria fowleri from water and soil samples by nested PCR. Parasitol Res. 2004;93: 211–17.
- Wellings FM, Amuso PT, Chang SL, Lewis AL. Isolation and identification of pathogenic Naegleria from Florida lakes. Appl Environ Microbiol. 1977;34:661–7.
- John DT, Howard MJ. Seasonal distribution of pathogenic free-living amebae in Oklahoma waters. Parasitol Res. 1995;81:193–201.
- Duma RJ. Study of pathogenic free-living amebas in fresh-water lakes in Virginia. EPA Publication. 1980;EPA-PB-126369, Summary, 1981 is EPA-600/S1-80-037.
- Ettinger MR, Webb SR, Harris SA, McIninch SP, C Garman G, Brown BL. Distribution of free-living amoebae in James River, Virginia, USA. Parasitol Res. 2003;89:6-15.
- Kemble SK, Lynfield R, DeVries AS, Drehner DM, Pomputius WF 3rd, Beach MJ, Visvesvara GS, da Silva AJ, Hill VR, Yoder JS, Xiao L, Smith KE, Danila R. Fatal Naegleria fowleri infection acquired in Minnesota: possible expanded range of a deadly thermophilic organism. Clin Infect Dis. 2012;54:805-9.
- US Census Bureau. Statistical Abstract of the United States: 2012. Arts, Recreation, and Travel: Participation in Selected Sports Activities 2009. [XLS – 1 MB] 2012.
- 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.
- Cabanes PA, Wallet F, Pringuez E, Pernin P. Assessing the risk of primary amoebic meningoencephalitis from swimming in the presence of environmental Naegleria fowleri. Appl Environ Microbiol. 2001;67:2927-31.