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 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. 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 States 1-3,, particularly in southern-tier states 4-8, but has recently caused infections as far north as Minnesota 9. No data exist to accurately estimate the true risk of PAM. Hundreds of millions of visits to swimming venues occur each year in the U.S. 10 that result in 0-8 infections per year 11. It is unknown why certain persons 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 risk 12. 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 31 reported infections in the U.S. in the ten years from 2012 to 2021, despite hundreds of millions of recreational water exposures each year 10. By comparison, in the ten years from 2010-2019, there were an estimated 3,957 unintentional drowning deaths each year in the US.
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- 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.
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- 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.