Tap water samples from the two homes both contained Naegleria fowleri, a tiny ameba that can travel from the nose to the brain and cause fatal infections.

The Louisiana residents, a 28-year-old man and a 51-year-old woman, both used neti pots to rinse their sinuses, and researchers believe they may have inadvertently given the bug a free pass to their brain while doing so.

Nestled in the warm fluid inside the skull, N. fowleri quickly started multiplying and feeding on the brain, killing its host within days, explained Jonathan Yoder, an epidemiologist at the CDC in Atlanta.

"Even though this is a very rare condition, it is certainly very tragic for those involved and their families," Yoder told Reuters Health.

Neti pots are teapot-like containers commonly used to wash the nose and remove dirt or dust there or loosen thick mucus. Earlier this month, the Food and Drug Administration issued a warning against using the pots with untreated tap water, which may contain bacteria and other microbes. Stomach acid usually wipes out the bugs, but the nose and sinuses don't have the same defenses.

The first signs of danger came in June 2011, when a man from southern Louisiana suddenly got a bad headache. His neck felt stiff, his back hurt and he vomited intermittently, according to the CDC report, which was published in the journal Clinical Infectious Diseases.

The following day he was brought to a New Orleans hospital in a combative state and with a fever. There was so much pressure in his central nervous system that when the doctors did a spinal tap, the cerebrospinal fluid shot out more than two inches. It was cloudy, when it should have been clear.

Despite getting shots of powerful antibiotics, the man was declared brain dead on June 8, three days after he first developed symptoms.

A few months later, a woman from northern Louisiana landed in the hospital after having spent three days with high fever and vomiting. She also had a stiff neck and was lethargic. She died on October 2 after five days at the hospital.

The CDC determined based on tissue samples that both persons died of primary amebic meningoencephalitis, or PAM, caused by N. fowleri.

Yoder said the CDC sees only a few cases of PAM every year, nearly all of them associated with swimming in lakes or other untreated water. But according to colleagues and family of the deceased, they had not been in contact with freshwater - other than at the house - in the weeks before their deaths.

Given that both persons used neti pots and that N. fowleri was found in the tap water, Yoder said it's likely that the sinus rinsing is to blame.

"It really requires a very specific forcing up the nose for (the ameba) to cross into the brain," Yoder explained. "It is not a typical parasite who is looking to infect humans. It is very happy to live in the environment."

SALT NOT ENOUGH

The two Louisiana deaths are the first U.S. cases of PAM that have been linked to N. fowleri in household plumbing served by municipal water. Yoder said he did not know how the ameba got into the plumbing in the first place, as it was not found in samples from the municipal water treatment plant.

But the investigation shows that once N. fowleri is in the plumbing, it is able to survive there, said Yoder. And adding salt to the water, as is typically done with neti pots, is not enough to take care of the microbe, the CDC found.

"We found that it does kill the amebas but it takes something like 18 hours for most of them to die," Yoder said. "It highlights the point that we should use safe water to mix with the salt."

For safe nose rinsing, health officials recommend using sterile or distilled water bought in stores, or tap water that is boiled for at least three minutes and then cooled, or water that has been passed through a filter with a pore size of no more than 1 micron.

SOURCE: bit.ly/OnNiER Clinical Infectious Diseases, online August 22, 2012.

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