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.
Measles can be dangerous and lead to complications
Most people survive a measles infection. After they do, they are considered to have lifelong immunity from subsequent exposures.
But infection puts people at a higher risk of complications, including pneumonia, ear infections, neurological symptoms and encephalitis, or swelling of the brain. In rare cases, measles is deadly. Three people in the U.S. died last year from the disease, CDC data shows.
The people who are most vulnerable to serious illness include those who are unvaccinated, young children, pregnant women and people with immune systems that are weakened because of genetic disorders, chronic diseases or cancer treatment.
The measles virus attacks healthy immune cells, Mulye explained. It causes immunological amnesia, “which is basically making your immune cells forget what they know.”
“And what they know is what they have been exposed to so far. Or whatever vaccines they have had, they store it as a memory in the body,” she said. “Measles virus infects those cells and starts killing them.”
That leaves people exposed to all sorts of other common viruses, bacteria and diseases that their body can no longer fight off, Mulye said.
Effectiveness of vaccinations, past and present
The American Academy of Pediatrics, as well as other national medical societies and organizations, upholds measles vaccination as the gold standard in protecting people from infection and preventing outbreaks.
One shot of the measles, mumps and rubella vaccine is recommended for all children at 12-15 months, and a second shot is recommended between ages 4 and 6, or when a child enters kindergarten.
The two-dose series prevents measles infection in about 97% of people, according to federal data compiled over six decades.
Adults born prior to 1957 are generally considered immune as they likely had already been infected before mass vaccination efforts. Other adults who may have received an inactivated measles vaccine used from 1963 through 1967 may need to be revaccinated to achieve immunity, according to the Pennsylvania Department of Health.
Tracking and tracing measles infection in Pennsylvania
Doctors, nurses and other health care providers are required to notify state or county health authorities as soon as they suspect that a patient is infected with measles. Information is shared at all levels of public health in real time, state officials said.
“Providers are advised not to wait for lab confirmation to notify public health officials if measles is suspected,” Pennsylvania Department of Health leaders told WHYY News in an email.
Throat swabs, urine and blood are collected for testing at the Pennsylvania Bureau of Laboratories to confirm cases officially.
The state shares confirmed cases and any information collected through contact tracing with the CDC, and vice versa. This becomes important in tracking cases involving people who live elsewhere, but who visit or pass through Pennsylvania in any capacity, including at major hubs like Philadelphia International Airport, while infectious with measles.
“Local, state, and federal public health officials work closely together to ensure that measles cases are identified, reported and confirmed as quickly as possible,” the health department stated.
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