Can I use tap water in my neti pot?

That was the interesting question I received yesterday at a birthday BBQ. Apparently and unbeknownst to me two different American individuals died after irrigating their sinuses due to the brain crawling and eating amoeba, Naegleria fowleri.  One case was reported in a 51 year old De Soto woman in northern Louisiana near the eastern Texas border and the other in a 20 year old St. Bernard man on the coast. Multiple agencies from the CDC to state health departments are issuing warnings to neti pot users to only use distilled, sterilized, or previously boiled water (1-3 minutes depending on altitude). Cases arising in Southern Australia from tap water nasal aspirations  and Arizona from tap water filled play pools have also been reported in the recent past.

Generally, N. fowleri is a free-living, freshwater, bacteria consuming amoeboid that transforms into cysts when it gets too hot or dry. However, it also feasts on central nervous tissue if given the chance, unlike 29 other Naegleria species. People tend to get infected when swimming in freshwater bodies of water when water gets inhaled into the nose. The mobile double flagellated stage can be induced to form if the trophozoite stage is washed with dilute salt solution or placed in distilled water. I suspect that this is the evolutionary escape stage triggered by inhospitable environmental conditions. I also wonder how this phenomenon would play out with neti pot use since the nasal wash is generally a mild saline. Does transformation into a more mobile stage make it more likely to migrate further into your sinuses? Or is the trophozoite stage simply being phagocytosed by structural cells lining the nasal epithelium called sustentacular cells as suggested by Visvesvara thus allowing the amoeba to travel even further inside your head? A further complication is that the amoeba has been found living in the throats and noses of healthy individuals. What makes it pathogenic? 

N. fowleri infection becomes a threat when temperatures increase and water levels decrease. Right now, we are still in the middle of a drought…and this summer will be prime time for increased brain eating amoeba caused meningitis. Normally, individuals come down with the disease after swimming in poorly chlorinated pools and freshwater bodies of water. The cyst stage can survive temperatures of 51-65°C or 123-149°F while the amoeboid stages can tolerate 10-50°C. Additionally, amoeba cultured at 30°C and 37°C were more pathogenic than those grown at 23°C and 44°C [in mice]. And just in case you didn’t know, 37°C equals 98.6°F. It makes sense from an ecological viewpoint that an organism grown and adapted to temperatures similar to mammalian host temperatures will be more pathogenic. When the water is the same temperature as your body, beware.

Yesterday at the party I didn’t know what to tell my friend, I assumed that effective water sterilization took place at water treatment plants and the chlorine concentration used was enough to kill the cyst, flagellated, and trophozoite life stages. In fact according to Jonckheere’s 1975 paper, “viable Naegleria cysts are not to be found in clean water where low concentrations of chlorine are constantly maintained.” Visvesvara also reports that chlorine levels at 1 ppm are enough to kill the amoeba. It seems that either the water treatment plants aren’t doing their job or the water is getting contaminated after leaving the plant. The Louisiana State Department of Health has already attributed these deaths to “improper use of neti pots” as opposed to the failure of local water treatment plants to insure safe water. They have also stated that tap water is safe for drinking but not for nose irrigation. I didn’t know that the only safe use of tap water was for drinking, I would have thought it safe for other hygienic purposes as well. This more or less seems like a legal move to me, a way to shift the blame away from themselves and to neti pot users.

Until this question yesterday, I never would have second guessed using tap water for nose irrigation. Should we also not rinse contact lenses or eyes when they come in contact with chemicals with tap water for fear of Acanthamoeba spp. infecting our corneas? I would be concerned if my water treatment plants were unable to kill N. fowleri, what other pathogens are slipping by and into the water supply?

But back to the question at hand? Should my friend use tap water in her neti pot? I would say definitely yes if it has been boiled or passed through a filter with an absolute pore size of 1 micron or smaller (not nominal pore size). I would also say yes if the weather has been cool and wet. However, I can’t say yes if both a drought and high temperatures are co-occurring. So the safest course of action is to follow the CDC guidelines (http://www.cdc.gov/parasites/naegleria/faqs.html). And hey, it might be worth it to buy a fancy water filter, you’ll not only be protecting yourself from amoeboid meningoencephalitis but also Giardia, Cryptosporidium, lead, and many other contaminants. 

John, D.T. (1982). Primary Amebic Meningoencephalitis and the Biology of Naegleria Fowleri. Annual Review of Microbiology, 36, 101–123.

De Jonckheere, J. & van de Voorde, H. (1976). Differences in destruction of cysts of pathogenic and nonpathogenic Naegleria and Acanthamoeba by  chlorine. Applied and Environmental Microbiology, 31, 294–297.

Visvesvara, G.S., Moura, H. & Schuster, F.L. (2007). Pathogenic and opportunistic free-living amoebae: Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri, and Sappinia diploidea. FEMS Immunology & Medical Microbiology, 50, 1–26.

Author
Stavana Strutz is a doctoral candidate studying disease ecology and evolution  in the Parmesan lab at the University of Texas at Austin.