A 40-year-old woman has died from measles complications in Pennsylvania, marking the state’s third measles-associated death this year as the U.S. experiences its worst resurgence of the highly contagious disease in 35 years.

The woman, a Jefferson County resident, died on Saturday, county Coroner Greg Furlong said on Facebook.

“This is a heartbreaking loss for the family and an unfortunate reminder that measles can be a serious and potentially life-threatening disease,” Furlong said.

No other information about the woman will be released, he added.

The Pennsylvania Department of Health said it was aware of the death reported by the Jefferson County coroner.

“The Department of Health is conducting a thorough review of this case and will provide the public with updated information when it becomes available,” health officials said in a statement.

At least 676 measles cases have been confirmed in 37 counties in Pennsylvania so far this year, the state’s health officials reported Friday. The outbreak has hospitalized 124 people in the state. Of the confirmed cases, fewer than 1% had been fully vaccinated, Pennsylvania health officials said.

The woman is the third person reported to have died in connection with measles in Pennsylvania. The two other measles-related deaths involved infants, according to the Lancaster County coroner, Dr. Stephen Diamantoni.

Measles symptoms typically begin with a cough, fever, runny nose and red, watery eyes, followed by a red rash. The disease can cause severe complications, including pneumonia and swelling of the brain.

The Jefferson County coroner’s office is working with Pennsylvania health officials on the case, Furlong posted.

The U.S. is experiencing its largest measles outbreak since 1991, with more than 3,000 confirmed cases this year, according to the Centers for Disease Control and Prevention.