Photo Credit Florida DOH
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Nearly every year we see a small number of cases of a rare, mostly fatal brain infection caused by free living amoebas (Naegleria fowleri) that inhabit warm, fresh water (see A Reminder About Naegleria Season - 2019).
Dubbed the `brain eating amoeba' by the press - this infection is called PAM (Primary amebic meningoencephalitis) - and occurs when the amoeba enters the brain through the nasal passages, usually due to the forceful aspiration of contaminated water into the nose.
As a thermophilic (heat-loving), free-living ameba, it is hardly surprising that is is mainly reported in the summer and that Florida and Texas lead the nation in cases over the past three decades, although infections have occurred as far north as Minnesota.
About 10 days ago the CDC's MMWR carried a report on a fatal 2024 case from Texas, which involved a previously health 71-year old woman who used unsterilized water to perform nasal irrigation.
Sadly, this is a common way that people around the world have become infected (see 2011's Neti Pots & Naegleria Fowleri). Other routes of infection include swimming in stagnant, warm fresh water ponds, attending water parks, and even in a child playing with a water hose in their own yard.
Weekly / May 29, 2025 / 74(19);334–335
Olivia A. Smith, PhD1; Whitney Tillman, MPH1; Jantel B. Lewis, MPH1; Stephen White, PhD1; Mia Mattioli, PhD2; Julia Haston, MD2; Megan Dorris, MMS2; Amy Kahler, MS2; Alexis Roundtree2; Ibne Karim Ali, PhD2; Shantanu Roy, MS2; Taylor Yakubik, DO3; Lauren Sisco, MD3; Jasen Kunz, MPH2Summary
What is already known about this topic?
Primary amebic meningoencephalitis (PAM) is a rare, often fatal brain infection caused by the free-living ameba Naegleria fowleri. Using tap water for nasal irrigation is a risk factor for PAM.
What is added by this report?
A fatal case of PAM occurred in an otherwise healthy adult woman who used tap water obtained from her recreational vehicle (RV) in a nasal irrigation device. Although N. fowleri was not isolated from the RV water supply, the water was found to be inadequately disinfected.
What are the implications for public health practice?
This case highlights the importance of following recommended nasal irrigation practices. Improperly maintained RV water systems can be a source of waterborne disease, including PAM.
The CDC and state health departments have long warned on the dangers of using tap water to perform nasal irrigation, and offer advice on safer alternatives.
Only 3 or 4 cases are reported in the United States each summer, but in 2017 a research letter written by epidemiologists at the CDC (see EID Journal: Estimation of Undiagnosed Naegleria fowleri (PAM), United States) estimated the yearly number PAM cases in the United States probably averages closer to 16 (8 males, 8 females).
Meaning that 70%-80% likely go unrecognized.
The State of Florida's Primary Amebic Meningoencephalitis (PAM) website recommends:
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:
- Avoiding water-related activities in bodies of warm freshwater, hot springs, and thermally-polluted water such as water around power plants.
- Avoiding water-related activities in warm freshwater during periods of high water temperature and low water levels.
- Holding the nose shut or using nose clips when taking part in water-related activities in bodies of warm freshwater such as lakes, rivers, or hot springs.
- Avoiding digging or stirring up 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, use water filtered with an absolute filter 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.
