Philadelphia health officials are tracking a measles outbreak: What to know

The Philadelphia Department of Health is tracking a measles outbreak in the city, with eight confirmed cases as of Monday.

Health officials told ABC News all confirmed cases are among non-immune individuals.

The health department said it's actively tracking current cases and has listed several known exposure sites across the city, mostly at health care facilities and a daycare.

The first known case was identified as a patient who was admitted to the Children's Hospital of Philadelphia in early December, where three other non-immune children were exposed and later tested positive for the virus, health officials said. At least three of the cases have resulted in hospitalization.

Health officials recommend anyone who thinks they may have been exposed to quarantine alone at home and stay away from other people.

Measles is one of the most contagious infectious diseases and can easily spread from one case to dozens of others in a contained area, said Dr. Indi Trehan, a pediatric infectious disease specialist at the University of Washington/Seattle Children's Hospital. According to the Centers for Disease Control and Prevention, measles virus particles can remain infectious for up to two hours once airborne.

After an initial flu-like illness, patients with measles can develop, ear infections, severe diarrhea, superimposed pneumonia, or brain infection and swelling. "It's a 'surface' disease, which means that all the major exposed surfaces of your body get broken down, like your respiratory tract, GI tract and eyes," Trehan said.

Measles infection can lead to blindness, weakness of the immune system and even rare neurologic symptoms years later in life. According to the Philadelphia Department of Health, one in five patients require hospitalization.

Individuals with measles should follow strict isolation measures, or risk spreading it to unvaccinated individuals. High-risk groups for serious illness include young children, the elderly, pregnant people and people with weakened immune systems.

The CDC recommends vaccination with the measles, mumps and rubella (MMR) vaccine at 12 to 15 months of age, and again at 4 to 6 years of age. There is no known treatment for measles besides supportive care and giving vitamin A to help reduce the risk of death. Experts do not recommend giving vitamin A to prevent measles.

The measles vaccine has prevented 56 million global deaths between 2000 and 2021, according to the World Health Organization. The United States declared measles an eliminated disease in 2000, but outbreaks have been increasing from unvaccinated individuals due to immigration, disrupted vaccine schedules from COVID-19 isolation regulations, and growing vaccine hesitancy since a debunked study falsely linked the MMR vaccine to autism.

The only way to prevent measles is to get the highly effective MMR vaccine, said Dr. Danielle Zerr, medical director for infection prevention at Seattle Children's Hospital.

"We have to hear families out and respect their concerns and fears, and provide them data-driven evidence and stories that illustrate why it's so important to be vaccinated," Zerr said. She recommended parents and caregivers use reputable sources to answer questions about the vaccine, such as the CDC or their pediatrician.

Trehan encouraged parents and caregivers who notice symptoms of measles in their child to call their local health care center ahead of time so the facility can prepare precautions. These symptoms include a high fever of around 103 to 105 degrees, copious congestion, red eyes, a rash that spreads head to toe and extreme irritability, according to the CDC.

"It's on all of us to protect each other as a society, as a human family," Trehan said.

Angela Y. Zhang, M.D. (she/hers), is a pediatric resident at the University of Washington/Seattle Children's Hospital and a member of the ABC News Medical Unit.

Jade A. Cobern, M.D., MPH, is a board-certified pediatrician, specialized in general preventive medicine, and is a member of the ABC News Medical Unit.