Two children and a young man have died this summer from a rare amoeba that lives in water, U.S. health officials say.

This month, the brain-destroying infection killed a 16-year-old Florida girl, who fell ill after swimming, and a 9-year-old Virginia boy, who died a week after he went to a fishing day camp. The boy had been dunked the first day of camp, his mother told the Richmond Times-Dispatch. A 14-year-old boy died in 2007 after being infected with a brain-destroying amoeba that doctors say he probably picked up while swimming in Lake Havasu, Ariz., seen here. Dave Cruz/The Arizona Republic/AP

Those cases are consistent with past cases, which are usually kids — often boys — who get exposed to the bug while swimming or doing water sports in warm ponds or lakes.

The third case, in Louisiana, was more unusual. It was a young man whose death in June was traced to the tap water he used in a device called a neti pot. It's a small teapot-shaped container used to rinse out the nose and sinuses with salt water to relieve allergies, colds and sinus trouble.

Health officials later found the amoeba in the home's water system. The problem was confined to the house and wasn't found in city water samples, said Dr. Raoult Ratard, Louisiana's state epidemiologist.

The young man, who was only identified as being in his 20s and from southeast Louisiana, had not been swimming or in contact with surface water, Ratard added.

He said only sterile, distilled or boiled water should be used in neti pots.

The illness is extremely rare. About 120 U.S. cases — almost all of them deaths — have been reported since the amoeba was identified in the early 1960s, according to the U.S. Centers for Disease Control and Prevention.

Infections a medical mystery

About three deaths are reported each year, on average. Last year, there were four.

There are no signs that cases are increasing, said Jonathan Yoder, who co-ordinates surveillance of waterborne diseases for the CDC.

The amoeba — Naegleria fowleri (nuh-GLEER-ee-uh FOWL-er-eye) — gets up the nose, burrows up into the skull and destroys brain tissue. It's found in warm lakes and rivers during the hot summer months, mostly in the South.

People cannot be infected by drinking water contaminated with the amoeba or from a properly cleaned, maintained and disinfected swimming pool, according to the CDC's web site. The infection cannot be spread from one person to another.

It's a medical mystery why some people who swim in amoeba-containing water get the fatal nervous system condition while many others don't, experts say.

But the cases that do occur tend to be tragic, and there's only been one report of successful treatment.

"It's very difficult to treat. Most people die from it," Ratard said.