Nasal-irrigation devices called neti pots are involved in two recent deaths believed to be caused by amoebas that entered people’s brains via their sinuses while using the pots, health officials say.

In both cases in Louisiana, the neti pots were filled with tap water instead of the recommended distilled or sterilized water. The water was then flushed up their noses, a deadly amoeba called Naegleria fowleri found its way to their brains, where it caused an infection that destroys brain tissue and can kill its host within days.

If confirmed, the incidences will be the first in which the amoeba survived the water treatment process.

“Nearly all the cases have resulted from exposure to warm recreational water, such as ponds, rivers and lakes, and the kind of exposure where the water would be forced up the nose,” said Jonathan Yoder, an epidemiologist with the U.S. Centers for Disease Control and Prevention. “In the last 15 years, I’m not aware of other cases associated with treated drinking water.”

Chlorine, a part of the water treatment process, may kill 99.9 percent of amoebas, parasites, bacteria, viruses in water – but not all, he explained.

“While we say our drinking water is safe, it’s not sterile,” Yoder adds.

N. fowleri infection is rare in the U.S. Just 32 cases have been documented between in the past decade, according to the CDC.

Symptoms of primary amebic meningoencephalitis, the infection caused by the amoeba, include headache, fever, nausea, vomiting, and a stiff neck – later symptoms include disorientation, seizures, and hallucinations. Symptoms may not appear for up to a week after exposure.