If you're going to pour water up your nose, at least make sure it's been boiled, distilled, or filtered, officials say - otherwise you could be at risk for a life-threatening brain infection.

Two Louisiana residents died in 2011 from an infection caused by an amoeba that was likely delivered directly to their brains via a neti pot, a device that some people use to flush out their sinuses. Those two cases are the first time the U.S. Centers for Disease Control and Prevention has been able to solidly link a brain infection to neti pots.

The particular culprit in the two cases is the amoeba Naegleria fowleri, which likes to swim around in warm freshwater. Normally, N. fowleri is content to feed on bacteria, but if it finds itself inside a human, it can feed on a person too.

N. fowleri infections are very rare - there were only 5 cases in 2011. Typically, a person picks up the amoeba after swimming in a lake or pond and inadvertently snorting some water up their nose. But in the Louisiana cases, while tests confirmed that the two patients died from N. fowleri, the victims had not swam or otherwise recreated in freshwater at any point in the two weeks before they became sick.  

When the CDC investigated, they found that both victims regularly practiced nasal irrigation with neti pots. Tests of their home plumbing showed that N. fowleri was present in both patients' tap water.

So should the average person be worried about drinking brain-eating amoebas from the faucet? Short answer: not really.

"Treated tap water for the most part is very safe, but it's not sterile. There are organisms in tap water that your stomach easily takes care of, but which your brain is not designed to handle," says Jonathan Yoder, a CDC researcher who worked on the neti pot investigation.

In other words, while N. fowleri is quickly eviscerated by stomach acids if you drink it up, forcing it into your sinuses is another story, since your nose doesn't have anything in the way of an acidic defense. If the amoeba crosses into a person's brain it can start feeding on tissue, prompting an inflammatory response that causes brain swelling. Symptoms of an N. fowleri invasion include headache, vomiting, fever, stiffness in the neck, and confusion, with death usually coming about 5 days after a person starts showing signs of infection.

Yoder and his colleagues say if a person is going to use a neti pot, they should use water that's been sterilized in some way - distilled, boiled or filtered with a filter that has an absolute pore size of 1 micron or less.

N. fowleri could also enter your body through your eyes, so the same rules apply for rinsing contact lenses with tap water, according to Yoder.

Some neti pot makers already contain instructions on what kinds of water to use with their products , but government officials are now looking into whether those labels are enough to put consumers on their guard.

"The FDA is working with manufacturers to make sure they have all the right warnings in place," Yoder says.

SOURCE: Yoder et al. "Primary Amebic Meningoencephalitis Deaths Associated With Sinus Irrigation Using Contaminated Tap Water." Clinical Infectious Diseases published online 22 August 2012.