"We didn't have any clue what was going on, but when we got the actual tissue we could see it was the amoebae", Dr. Charles Cobbs, a neurosurgeon at Swedish Medical Center, told the Seattle Times.
When Dr Cobbs next operated on the woman, the growth had grown to the size of a baseball, and that too much of her brain tissue had been killed for medics to save her.
What happened: The woman had been filling her neti pot with unfiltered water and using it to try to clear up a sinus infection.
Dr Cobbs continued: 'It's extremely important to use sterile saline or sterile water.
In the case of the Seattle woman, she likely became infected with the amoebas from her tap water, according to the researchers.
Three types of amoebas have been identified as causing fatal brain infections, according to Jennifer Cope, an epidemiologist with the Centers for Disease Control and Prevention's unit that focuses on foodborne, waterborne and environmental diseases.
The case is the second-ever reported in Seattle - the first was in 2013.
She used the neti pot for about a month to treat her sinus infection, and developed red, rash-like sores around her nose. But then Hopkins pathologists came back with a verdict: The infection looked "amoebic", said Cobbs, who thought, "that's ridiculous", upon hearing the news. "This precedent led us to suspect the same route of entry for the ... amoeba in our case". However, during the surgery, the doctors discovered that, in reality, that formation was not a brain tumor but a rare brain-eating amoeba.
"She had not been boiling water, using sterile water or using sterile saline".
Amoebas may be found in fresh-water sources around Puget Sound such as wells, but aren't present in city-treated water, according to Liz Coleman, a spokeswoman for the Environmental Public Health division of the state's Department of Health. 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.
A year on, the woman started to develop some unusual symptoms, such as a odd red rash around the outside of her nasal passage.
According to Dr. Zara Patel, a professor of otolaryngology at Stanford University, when people use contaminated water to rinse their nose and sinuses, they can be at risk for aggressive infections. And it's hard to grow the amoeba in the lab, because it doesn't grow on agar, a commonly used cell-culturing medium used in labs. It moves slowly and can take weeks or months to cause death. "MRSA (a treatable bacterial infection) is everywhere, but we don't have a mechanism of injecting it into our brain", Cobbs said.