CDC statistics show over 700 Americans have been diagnosed with measles so far in 2019.
It's the most cases in a single year since 1994.
The disease is now confirmed to be in Pennsylvania. Earlier this week, an adult in Allegheny County was diagnosed. That person was not vaccinated.
According to the CDC, that's the case with the majority of the people who are falling ill to the disease.
"Measles virus is one of the most contagious viruses known to mankind," said Tibisay Villalobos, a pediatric infectious diseases doctor at Lehigh Valley Health Network's Reilly's Children's Hospital.
That's why concerns are growing as outbreaks continue to pop up across the country.
"Younger children can get viral pneumonia that can be very severe or secondary bacterial pneumonia, it can affect the central nervous system, it can also cause meningitis, which is inflammation of the layers of the brain," added Villalobos.
Symptoms typically begin one to two weeks after a person is infected and include coughing, runny nose, watery eyes, and a high fever. A rash also appears a few days after initial symptoms.
"So by the time the rash appears and someone thinks 'That may be measles,' the patient has exposed a lot of people with the cough, congestion and respiratory infection," said Villalobos.
Infants and the elderly are most susceptible to contracting measles. But doctors recommend vaccination to anyone who doesn't have two doses.
"Everybody should have two doses of the measles vaccine to be completely immunized and protected," said Villalobos.
According to the CDC, three-quarters of this year's cases are in unvaccinated people. Local pediatricians are seeing proactive trends with parents.
"We have parents calling to have their children get the vaccine ahead of time because of the potential exposure if they're gonna be traveling, going to summer camps, they're getting out of school," added Villalobos.
Schools keep track of students who aren't vaccinated in case an outbreak were to happen in their community.
"We do definitely keep a record of that, who's immunized and who's not, just in case there is an outbreak in our building or out in the public, to let parents know," said Lisa Lienhard, school nurse at Jim Thorpe High School.
During a nationwide outbreak, health professionals say the most important thing is to be aware of what's happening in your area.
"Bringing awareness every day is making people think about it and families and parents are really thinking about it, asking their doctors what is the best time," added Villalobos.
"I think we just have to keep ourselves informed of what's going on and take a look at the big picture and see what we can do to protect ourselves and keep this from going any farther," said Lienhard.
Doctors are also stressing the importance of vaccination right now as these outbreaks are happening just ahead of the summer travel season.