A fourth person in Pennsylvania has died of measles, the state health department confirmed Tuesday. The latest death was in an unvaccinated 18-year-old resident of Mifflin County.

In the announcement, the state health department also confirmed a county coroner’s report over the weekend of the death of an unvaccinated 40-year-old woman in Jefferson County. The state had previously reported two deaths in Lancaster County; both were infants—a newborn boy and a 6-week-old girl, both too young to be vaccinated.

According to the Mifflin County coroner, Andrea L. Alcalde, the 18-year-old’s cause of death was determined to be acute disseminated encephalomyelitis (ADEM), which is a rare but known severe complication of measles. The condition is characterized by a rapidly progressing autoimmune disorder in which aberrant inflammation from an infection strips away the protective coverings of nerve cells in the brain and spinal cord. Before measles vaccines were widely used, ADEM was commonly associated with measles, though other viral infections can also spur its development.

In a new release posted to the coroner’s Facebook page Tuesday, Alcalde said the death determination was made after a review of medical records and all available information. Alcalde said no other information would be released about the deceased.

The state health department released a statement confirming the measles death of the 18-year-old, as well as the death of the 40-year-old. The two deaths will be added to the state’s outbreak data dashboard Wednesday as part of the regular update, the department noted.

Death reporting

So far, the state has reported 693 measles cases in 38 counties this year. There have been 99 cases reported in the last seven days. In all, 133 people have been hospitalized.

“My thoughts are with the two families who lost loved ones to this highly contagious virus, as Pennsylvania faces the worst measles outbreak in more than three decades,” Pennsylvania Secretary of Health Debra Bogen said in a statement, referring to the two latest deaths. “We remain committed to working with our partners across Pennsylvania to stem this outbreak and prevent more deaths. That means ensuring people have the facts about measles and access to the MMR [measles, mumps, and rubella] vaccine—which kept measles outbreaks at bay for decades.”