A 68-year-old Seattle woman who died after contracting a rare brain-eating amoeba used regular tap water to rinse her sinuses, according to new research.

As noted in a new International Journal of Infectious Diseases case study, the infection was initially misdiagnosed as a brain tumor. During surgery to remove the suspected tumor, the lead neurosurgeon, Charles Cobbs from Seattle’s Swedish Medical Center, was taken aback by the extent of the brain damage. So he extracted a sample for further testing.