What to Know A woman who went to the midnight showing of "Avengers: Endgame" was diagnosed with highly-contagious measles.

Anyone who was possibly exposed should call HCA Health Referral Line at 1 (800)-564-8448 or their health provider.

Those infected with measles can spread it without showing symptoms.

A woman who went to the midnight showing of "Avengers: Endgame" at an Orange County movie theater last week was diagnosed with measles, and now health officials are warning others in the crowd that they may have been exposed.

The Placentia woman in her 20s, who had just returned from an international trip, was infected with measles when she went to see the midnight showing of the finale in the Avengers saga.

The Orange County Health Care agency said the woman visited the AMC Theater in Fullerton Thursday, April 25, and other moviegoers may have been exposed from 11 p.m. in the evening until 4 a.m.

Health officials were advising others who believe they may have been exposed to check their vaccination history, and notify their health providers, especially if they haven't had measles before.

Symptoms include inflamed eyes, runny nose, high fever, and an unexplained rash seven to 21 days after being exposed.

Theater employees said the news comes as a shock, especially after such a busy week with huge crowds eager to see "Avengers: Endgame."

"The last place I would ever expect it was at my job. I wasn't even expecting Orange County," AMC Fullerton employee Carlee Greer-McNeill said. "People, if you know you have the measles, please don't come to a movie theater, let alone a public place."

Another location where residents may have been exposed was in Fullerton is St. Jude Emergency Department between 7 and 9 a.m. April 27.

The woman who went to the theater was under quarantine after being diagnosed. She is considered infectious from April 23 to May 1.

This case is the fist reported in Orange County, on the heels of Los Angeles County announcing its sixth Tuesday.

The sixth case reported this week also occurred after a Southern California resident traveled to another country, and noticed symptoms after returning.

Health officials advise that if anyone believes he may have measles to contact his doctor by phone before coming in to the doctor's office.

Those with measles can also infect others before they are even aware that they have it. Measles is very contagious, and can stay in the air for up to 2 hours after the infected person has left the area.

Los Angeles County Exposure Spots

The following locations have been identified as potential measles exposures:

● LAX, Tom Bradley International Terminal, Gate 218 on April 23 from 4 p.m. to 7 p.m.

● Fox Auto Parks LAX Shuttle on April 23 from 4:30 p.m. and 7:30 p.m.

● Home Depot, 44226 20th St W, Lancaster, CA 93534, on April 26 from 8 a.m. and 11 a.m.

Orange County Exposure Locations

● 5 Hutton Centre Dr., Santa Ana, CA 92707, on April 23 — 25 from 7:45 a.m. to 7:15 p.m. daily

● St. Jude Emergency Department, 101 E. Valencia Mesa Dr., Fullerton, CA 92835, on April 27 from 7 a.m. to 9 a.m.

● AMC Movie Theater, 1001 S. Lemon St., Fullerton, CA 92832, on April 25 from 11 p.m. — April 26 at 4 a.m.

The majority of those with measles were unvaccinated.