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Los Angeles County officials are warning that residents may have been exposed to measles earlier this month.

Health officials have confirmed that a person who spent time at a movie theater and stores on the Westside has been diagnosed with measles. Considered one of the most contagious diseases in the world, measles spreads through coughing and sneezing but can linger in the air for up to two hours after an infected person leaves the room.

It has been a bad year for measles. As of last week, 1,250 people have been diagnosed with measles nationwide, compared to 372 in all of last year. Case numbers appear to have peaked in April this year and have been falling since, according to national data.

In Los Angeles County, there have been 18 cases among residents so far, in addition to 11 people who traveled through the county while sick with measles. The majority of those who became sick were not immunized, officials said.

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