US Health authorities confirmed the first fatality from measles in 12 years, after a woman from rural northwestern Washington died from pneumonia caused by the contagious disease.
"The cause of death was pneumonia due to measles," said a statement from the Department of Health in Clallam County, Washington. "The woman had several other health conditions and was on medications that contributed to a suppressed immune system," it added.
Her name and age were not made public.
"The woman was most likely exposed to measles at a local medical facility during a recent outbreak in Clallam County," said the statement. "She was there at the same time as a person who later developed a rash and was contagious for measles."
Officials said she did not show common measles symptoms so the infection was not discovered until after her death, which occurred in the spring.
A spokesman for the health department told AFP that the woman's death was not related to the outbreak this year linked to a Disney theme park in California.
The type of measles the woman died of "matched the outbreak in the local county here, but that outbreak strain was not a match for the Disney outbreak," he said.
There have been 176 cases of measles in the United States so far this year, with 117 of those cases linked to the Disney outbreak, according to the US Centers for Disease Control and Prevention.
The last US death from measles was in 2003.
"This tragic situation illustrates the importance of immunizing as many people as possible to provide a high level of community protection against measles," the department of health said.
"People with compromised immune systems often cannot be vaccinated against measles."