A Seattle woman died after becoming infected with a brain-eating amoeba. The woman told her doctor she had used tap water in a Neti pot, instead of saline or sterile water, CBS affiliate KIRO reports. Doctors believe an amoeba entered in through her upper nasal cavity and got into her bloodstream, eventually reaching her brain.

A neurosurgeon from Swedish Medical Center in Seattle said this is a rare situation but is warning patients to be sure to follow the directions when using a Neti pot for nasal congestion, and use only boiled or distilled water. It's believed that the woman used tap water she'd put in a pitcher with a filter.

The neurosurgeon, Dr. Charles Cobbs, operated on the 69-year-old woman last January. She arrived in the hospital's emergency room after suffering seizures. At first doctors thought the woman had a tumor, as she had been previously diagnosed with breast cancer. She also had a sore on her nose that would not go away.

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When Cobbs first operated on her, he discovered a tumor the size of a dime. He removed it and sent a sample to a pathologist at Johns Hopkins for a second opinion.

"He thought it looked suspicious for amoeba infection. I was pretty much shocked because I'd never seen that before," Cobbs told KIRO-TV.

The woman's condition quickly deteriorated. About two weeks later, Cobbs performed another surgery and removed a mass the size of a baseball. Infectious disease doctors contacted the Centers for Disease Control and Prevention in Atlanta and they sent medicine for the rare condition, but the woman could not be saved.

How brain-eating amoeba infections happen

According to the CDC, most brain infections from amoebas are associated with swimming in warm freshwater lakes and rivers. However, very rarely, there have been deaths associated with an amoeba in tap or faucet water going up the nose.

A person cannot get infected from swallowing water contaminated with it, and it cannot pass from person to person. Infection can only occur when infected water goes up the nose.

The woman's doctors say they think her death was ultimately tied to her use of the Neti pot.

"She had not been boiling water, using sterile water or using sterile saline. She had been using water that had been put through a filter and maybe it had been sitting there and somehow the amoeba from somewhere else got in there. So that's what we suspect is the source of the infection," said Cobbs. "This is so rare there have only been like 200 cases ever."

Doctors who treated the woman also believe that the sore on her nose was connected. They wrote a case study for the International Journal of Infectious Diseases to educate other doctors on their rare findings.

"I believe it actually got in the bloodstream and somehow ended up in the brain. Because it wasn't directly from the nose to the brain, it somehow ended up in the brain way back here," said Cobbs, pointing to the back of his head.

Health officials say Neti pots can be safe to use as long as you follow the instructions and fill them only with boiled or distilled water.

"It's not something to be scared about because it's extraordinarily rare, but still there's a lot to learn," Cobbs said.

Last year the U.S. Food and Drug Administration also issued a warning that improper use of Neti pots and other nasal irrigation systems could lead to dangerous infections, including one with a brain-eating amoeba.

To use and care for your Neti pot or similar device, the FDA recommends:

Wash and dry your hands.

Check that the device is clean and completely dry.

Prepare the saline rinse, either with the prepared mixture supplied with the device, or one you make yourself.

Follow the manufacturer's directions for use.

Wash the device, and dry the inside with a paper towel or let it air dry between uses.

Talk with your health care provider or pharmacist if the instructions do not clearly state how to use it or if you have any questions. Also consult your doctor before using any nasal irrigation systems if your immune system is weakened for any reason.

Finally, some children diagnosed with nasal allergies as early as the age of 2 may benefit from nasal rinses. However, parents should consult with their pediatrician before use on children.