HARRISBURG, Pa. - Pennsylvania's measles outbreak continued to grow this week, with state health officials reporting 767 confirmed cases across 38 counties as of Friday, Sept. 18, an increase of 36 cases in two days.

The Pennsylvania Department of Health also reported 150 hospitalizations and four measles-associated deaths. On Wednesday, the state had reported 731 cases and 141 hospitalizations, meaning nine additional hospitalizations were added to the statewide totals between the two updates.

The increase does not mean every part of Pennsylvania is experiencing the same level of transmission. Cases are distributed unevenly across the 38 affected counties, and some parts of Western Pennsylvania have reported exposures without confirming resident cases. The statewide numbers nevertheless show that transmission remains active rather than winding down.

Cases continue climbing in September

The outbreak has expanded rapidly during September. Pennsylvania reported 594 cumulative cases on Sept. 8, 624 on Sept. 9, 676 on Sept. 11, 693 on Sept. 14, 731 on Sept. 16 and 767 on Sept. 18.

That means 173 cases were added to the state's cumulative total between Sept. 8 and Sept. 18. The number of affected counties increased from 37 to 38 during the same period.

Hospitalizations have also risen. The state reported 104 hospitalizations on Sept. 8 compared with 150 on Friday. Pennsylvania health officials say measles can cause pneumonia, brain swelling and other serious complications, and the state's current hospitalization total represents close to one in five confirmed cases.

Only four of Pennsylvania's 767 confirmed cases involve people who were appropriately vaccinated for their age, according to the Department of Health. The state says two doses of the measles, mumps and rubella vaccine provide about 97% protection against measles.

Western Pennsylvania has seen exposures and a death

The statewide outbreak has had direct effects in Western Pennsylvania even though the largest clusters have not been centered in Pittsburgh.

Allegheny County's Health Department said its most recently reported resident measles case remains a 2019 case, and its measles page listed zero current resident cases as of Sept. 14. That does not mean the Pittsburgh area has avoided exposure.

Two people who later tested positive for measles were at UPMC Children's Hospital of Pittsburgh on Aug. 27, according to the Allegheny County Health Department. Neither person was an Allegheny County resident. The county and UPMC identified patients and employees who may have been exposed in several areas of the hospital.

In Westmoreland County, the Pennsylvania Department of Health previously warned of a possible exposure at the New Stanton Service Plaza along the Pennsylvania Turnpike. An individual from outside Pennsylvania who later tested positive for measles visited the plaza on Aug. 17, potentially exposing people in several businesses, restrooms and dining areas.

The outbreak has also resulted in a confirmed measles-associated death in Jefferson County in Western Pennsylvania. The state announced Sept. 15 that an unvaccinated Jefferson County resident was one of two additional deaths it had classified as associated with measles. Another death was reported in Mifflin County.

Pennsylvania has reported four measles-associated deaths this year. The state uses an epidemiological definition that examines laboratory confirmation, timing of symptoms and other medical information when classifying a death as associated with measles. Federal and state officials have differed over how the deaths should be reflected in national statistics, and the Centers for Disease Control and Prevention is developing a standardized national definition with the Council of State and Territorial Epidemiologists.

Vaccination response expands

Pennsylvania has expanded vaccination efforts as case counts have climbed. The Department of Health said it administered more than 400 MMR vaccinations at 11 pop-up clinics during two days this week.

Since the outbreak began in late April, state health officials have administered nearly 4,800 MMR vaccinations through 148 pop-up clinics in affected communities. State health centers have administered more than 6,900 MMR doses statewide during 2026.

Demand has also increased through private health care providers and other vaccination sites. The state said Pennsylvania providers typically administer about 25,000 MMR doses in an average month. More than 46,000 doses were administered in August, followed by more than 25,000 during the first two weeks of September.

The Department of Health began the formal process of requesting an Epi-Aid from the CDC on Sept. 16. Epi-Aid teams can provide short-term epidemiological and technical assistance during urgent public health investigations. The state said Friday that discussions with the CDC about the scope of that assistance were continuing.

National outbreak remains elevated

Pennsylvania's outbreak is occurring during a broader resurgence of measles in the United States. The CDC reported 3,471 confirmed U.S. cases through Sept. 17. That national reporting cutoff is one day earlier than Pennsylvania's latest Sept. 18 total, so the two figures are not directly synchronized.

Measles spreads through the air when an infected person breathes, coughs or sneezes, and the virus can remain infectious in an enclosed space for as long as two hours after that person leaves. Symptoms generally begin seven to 21 days after exposure and can include fever, cough, runny nose and red or watery eyes, followed several days later by a rash that typically begins on the head and moves downward.

For Western Pennsylvania residents, the key point is that the statewide increase does not establish widespread local transmission in every county. Allegheny County continued to report no resident cases in its latest public update, while confirmed exposures have occurred in both Allegheny and Westmoreland counties and a measles-associated death has been reported in Jefferson County.

The Pennsylvania Department of Health continues to update its measles dashboard as new laboratory-confirmed cases are reported. People who believe they were exposed and develop symptoms are advised to contact a health care provider before arriving in person so precautions can be taken to avoid exposing other patients.