Los Angeles County health officials warned Monday that people who were at Los Angeles International Airport earlier this month may have been exposed to measles.

The warning is one of at least six that county officials have issued this year about a possible measles exposure at LAX, amid outbreaks in several other countries. Nationwide, there have been 1,276 cases this year, compared with 375 cases last year.

Measles is spread through the air. The virus can linger in a room for up to two hours after an infected person leaves, waiting to infect someone else, experts say.

“For those who are not protected, measles is a highly contagious and potentially severe disease that initially causes fever, cough, red, watery eyes, and, finally, a rash,” said L.A. County Health Officer Dr. Muntu Davis in a statement.