How do I know if I have been exposed to measles? Pittsburgh-area medical experts explain the symptoms

Many health experts find themselves increasingly concerned about the outbreak of measles in Pennsylvania. Now, with a confirmed case in Allegheny County, there is little doubt that other cases are out there and that it is extremely contagious. 

When someone is infected, they can be contagious and not even know the risk. 

As an airborne virus, measles flies on the fall breeze, and we have no way of knowing it's there. 

"It's the most contagious virus that we know; we have no other viral infection like this," said Dr. Robert Jackson of the Mayo Clinic. 

Dr. Jackson said that those who are carrying the virus are contagious days before they are symptomatic. 

"They're spreading the respiratory droplets in every room and hallway they're in and leaving it hanging in the air," he explained. 

Those droplets can't be seen by the human eye, and they stick in the air for a long time after the person has left the room or the area. 

"It's in the air, you breathe it in, and there you go," added Dr. Jillian Irwin, the Allegheny County Health Department's medical director. 

Dr. Irwin said it can be anywhere between 7 and 21 days before you start showing symptoms, and you're contagious before you feel it. 

"Four days before they get the telltale rash, and four days after," said Dr. Irwin. "The day you get the rash is [day] zero. That period before is when they're contagious." 

Now, according to Dr. Irwin, if you've received the measles-mumps-rubella vaccine or had measles as a child, you should be OK, but she added that 9 out of 10 people who have not been vaccinated will contract measles. 

According to the CDC, one out of five of those people will end up in the hospital. 

If you know that you have been exposed but haven't been vaccinated, you can get the vaccine within three days. 

"There's no guarantee that you're going to know if you are exposed within three days," Dr. Irwin explained. "That is why it's not worth the risk. People can get pneumonia; they can get brain swelling; it's a pretty severe situation. While it's not common, it's why we worry about measles." 

When it comes to the case of the child being exposed to measles at Target in McCandless, Dr. Irwin said they knew they were cutting it close with the warning. 

"There was one more day before people could potentially get immunoglobulin to help prevent measles," she said. 

Now, that window is closed. Dr. Irwin said this is very serious as now five people in Pennsylvania have died during this outbreak of measles. She said don't just assume it's a cold if you get a cough, runny nose, and watery eyes -- they could be symptoms leading up to the measles rash.