The first known US fatality from measles in 12 years was reported by public health officials in Washington State last week, according to Reuters.

The measles infection, which was previously undetected, was found by an autopsy of a deceased woman from Clallam County in northwestern Washington. The woman was most likely exposed to measles at a medical facility during a recent outbreak in the area, the state Health Department said in a statement on its website.

The woman never developed some of the common symptoms of measles, such as a rash, so her infection was not discovered until after her death, the agency said.

Her precise immunization status was unknown, and though she had measles anti-bodies, the woman also had several other health conditions and was on medications that suppressed her immune system, Health Department spokesman Donn Moyer said.

The cause of her death was ruled by medical examiners as pneumonia due to measles, according to the agency.

The last confirmed measles death in the United States was reported in 2003, according to the CDC.