The ultrastructural appearance of a single virus particle of the measles virus. (CDC/Getty Images)

Health officials on Thursday confirmed the country's first measles death since 2003, and they believe the victim was most likely exposed to the virus in a health facility in Washington state during an outbreak there.

The woman died in the spring; a later autopsy confirmed that she had an undetected measles infection, the Washington State Department of Health said in a statement. The official cause of death was announced as "pneumonia due to measles."

[Everything you need to know about measles]

The woman was at a Clallam County health facility "at the same time as a person who later developed a rash and was contagious for measles," the health department statement read. "The woman had several other health conditions and was on medications that contributed to a suppressed immune system. She didn’t have some of the common symptoms of measles such as a rash, so the infection wasn’t discovered until after her death."

The release did not provide any other identifying details, including the woman’s age.

According to the U.S. Centers for Disease Control and Prevention, 178 people from 24 states and the District were reported to have measles from Jan. 1 through June 26 of this year. Two-thirds of the cases, the CDC noted, were "part of a large multi-state outbreak linked to an amusement park in California."

This newly confirmed case marks Washington's 11th reported instance of measles this year, and state health officials urged people to vaccinate against the virus.

"This tragic situation illustrates the importance of immunizing as many people as possible to provide a high level of community protection against measles," the state health department's statement read. "People with compromised immune systems often cannot be vaccinated against measles."

Following the outbreak in his state, California Gov. Jerry Brown (D) this week signed one of the nation’s strictest laws regarding school vaccinations. Starting in the 2016-2017 school year, parents can’t claim personal belief exemptions, and medical exemptions will only be allowed for children with serious health problems.

[Jim Carrey denounces new Calif. vaccine law in Twitter rant]

Measles were effectively eliminated in the United States in 2000, according to the CDC. Health officials have said that the disease made a comeback recently, in part because of a growing number of adults deciding to delay or abstain from vaccinating their children. Last year brought the highest number of recorded measles cases since 2000, according to the CDC.

Earlier this year, President Obama acknowledged the concerns some have about effects of vaccines but said: "The science is pretty indisputable."

"You should get your kids vaccinated — it’s good for them,” Obama said. “We should be able to get back to the point where measles effectively is not existing in this country.”

This post has been updated.

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