At least 16 people have caught the measles in northern Manhattan and the Bronx, the NYC Health Department announced Friday.
Seven of the cases were adults, and four required hospitalization, the Associated Press reports. The Health Department says it's working to make sure the virus doesn't spread through hospital emergency rooms.
The Health Department is also reminding all New Yorkers that they should be vaccinated against the measles, and that they can check their immunity with a blood test to see if they need to be re-vaccinated.
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Measles is spread through the air from people who are coughing or sneezing, and it is extremely contagious. 1 in 10 children who get the measles will get an ear infection, according to the CDC, and 1 in 20 will get pneumonia. The disease causes fever, a runny nose, and a rash all over the body.