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Measles infections are sharply rising across the United States with 1,136 confirmed cases in the first two months of the year. That’s four times the number recorded at this point last year, federal data shows.
Pennsylvania has yet to see any large-scale outbreaks, but the state has reported 12 confirmed cases among residents, all of which have taken place in Lancaster, Montgomery and Chester counties.
Public health experts say people should get used to more frequent alerts and notices of measles exposures in their communities, especially at high-trafficked areas like airports and train stations, but also at medical offices.
Here’s everything to know about measles infections, how cases are tracked and traced in Pennsylvania, and what people can do to protect themselves and others.
Measles contagiousness is in a league of its own
Measles is one of the most contagious viral diseases in the world. One person with the virus can infect as many as 18 other people if they are unvaccinated, according to the World Health Organization.
It’s more infectious than influenza, COVID-19 and other common respiratory diseases, said Minal Mulye, an associate professor at the Philadelphia College of Osteopathic Medicine, who holds a doctorate in immunology and microbiology.
She said one reason is because measles lingers in the air and on surfaces for about two hours after someone with an infection has coughed, sneezed or breathed in that area.
“It is there even when the patient isn’t,” Mulye said.
That’s why measles exposure alerts from state and county health authorities will include specific locations and two-hour timeframes during which others were at risk of contracting the virus.
Another reason why measles is so contagious is because of its broad timeline of progression and symptoms, she said.
The earliest symptoms of a measles infection typically appear 10-12 days after exposure and can include high fever, cough, runny nose and conjunctivitis, or “pink eye,” according to the U.S. Centers for Disease Control and Prevention.
About two to three days later, people may see Koplik spots, which are bluish-white dots surrounded by red, inside the mouth, Mulye said.
A skin rash typically occurs about three to five days after onset of early symptoms. It can present as flat red spots or raised bumps that appear on the face and near the hairline before spreading down to other parts of the body.
A person with measles is capable of transmitting the virus to others four days before and four days after the appearance of the skin rash, CDC guidelines say.
People may not know they have measles in the days right before developing a rash, Mulye said, so they may not be isolating or quarantining just yet.
And since the red rash is an immune response to the infection, Mulye said people who are immunocompromised may not develop a rash at all but still have the virus.
Anyone who suspects they have a measles infection is encouraged to call ahead to their pediatrician, health center or primary care doctor before visiting in person, local health officials said.