On Thursday, state health officials announced that a Washington woman has died of measles, becoming the first American to be killed by the disease since 2003, the Associated Press reports.

In their announcement, the Washington State Department of Health said the woman presented few of the disease’s common symptoms and her infection was only discovered upon autopsy. From USA Today:

The woman was probably exposed to measles at a medical facility during a measles outbreak this spring, according to the health department. She was at the hospital at the same time as a patient who later developed a rash and was diagnosed with measles. Patients with measles can spread the virus even before showing symptoms.

The woman, who died of pneumonia, had other health conditions and was taking medications that suppressed her immune system, the health department said.

“This tragic situation illustrates the importance of immunizing as many people as possible to provide a high level of community protection against measles,” said department spokesman Donn Moyer in a statement. “People with compromised immune systems often cannot be vaccinated against measles. Even when vaccinated, they may not have a good immune response when exposed to disease; they may be especially vulnerable to disease outbreaks.”

[Image via AP Images]