Pennsylvania's measles outbreak claimed its third life this weekend, health officials confirmed, after a 40-year-old Jefferson County woman died Saturday in a case the county coroner says was driven by the virus.

Coroner Greg Furlong told reporters the woman was unvaccinated and had underlying chronic obstructive pulmonary disease, asthma, hypertension and high cholesterol, and had been on supplemental oxygen around the clock before her death. Furlong said he is working with the state health department, which confirmed it is conducting a "thorough review" to formally classify the death, according to Spotlight PA.

"THIS PERSON WAS PARTICULARLY COMPROMISED, WITH CHRONIC OBSTRUCTIVE PULMONARY DISEASE AND ASTHMA. THAT'S A PERSON WHO COULD WELL DIE FROM THIS VIRUS."

The death is notable for two reasons: it's the first tied to the outbreak outside Lancaster County, where the state's two earlier measles-associated deaths — both infants — occurred in August, and it's the first involving an adult. The Philadelphia Inquirer reported the woman had been exposed to several confirmed and unconfirmed cases before falling ill and had declined testing before she died.

As of Friday's count, Pennsylvania had logged at least 676 confirmed measles cases spread across 37 of its 67 counties — a tally state officials say has continued climbing toward 700 in the days since, per updated figures reported this week by outlets including PhillyVoice. Of those cases, 124 have required hospitalization, and four have involved people who were already vaccinated — so-called breakthrough infections that remain rare but have drawn attention from public health officials tracking the outbreak's spread since it began in late April.

The outbreak has become one of the largest measles flare-ups in the country this year, prompting the Pennsylvania Department of Health to run pop-up vaccination clinics statewide and push MMR shots for anyone who is unvaccinated or unsure of their status. Measles is among the most contagious viruses known, capable of lingering in the air of a room for up to two hours after an infected person leaves, and the Centers for Disease Control and Prevention considers two doses of the MMR vaccine about 97% effective at preventing infection.

State health officials have not yet finalized whether the Jefferson County death will be formally added to Pennsylvania's official measles fatality count, and the case had not yet appeared on the CDC's national outbreak tracker as of this week — a lag Spotlight PA noted reflects how state and federal death tallies for the outbreak have diverged. Furlong said he expects to update the death certificate designation to "probable" measles-associated after further consultation with the family. With the outbreak still active across more than half the state's counties, health officials are bracing for the case count — and the review into this latest death — to keep moving through the fall.