(CNN) California public health officials are warning moviegoers who went to see "Avengers: Endgame" and other films at an Orange County movie theater last Thursday that they may have been exposed to measles by a woman in the audience.
The woman attended a midnight screening of the "Avengers" blockbuster at the AMC Dine-In Fullerton 20 on Thursday from 11 p.m. to 4 a.m, the Orange County Health Care Agency said.
Everyone who was in the building may have been exposed, not just at that particular screening room, the agency said.
The warning also applies to people who went to buildings at 5 Hutton Centre Drive in Santa Ana from last Wednesday through Friday.
The woman, who is in her 20s, reported having recently traveled to a country with widespread measles activity, the agency added.
The agency said the woman was considered infectious between April 23 and Wednesday and is under voluntary isolation at home in Placentia.
It is the first confirmed measles case in the county this year.
Measles is a highly contagious disease caused by a virus that can spread through the air when an infected person coughs or sneezes or if someone comes into direct contact or shares germs by touching the same objects or surfaces. Symptoms may include fever, cough, runny nose, watery eyes and a rash of red spots.
Dr. Julia S. Sammons, a pediatric infectious disease specialist and medical director of the Department of Infection Prevention and Control at The Children's Hospital of Philadelphia, said once a person has measles, about 90% of close contacts who are susceptible to it will develop the disease.
Measles cases in the United States have surpassed the highest number on record since the disease was declared eliminated nationwide in 2000. Many of the cases have been in strongholds of vaccine-wary parents, swayed by anti-vax misinformation and distrust of authorities.
There have been 38 reported cases of measles in 11 California counties, according to the website of the California Department of Public Health. A total of 14 cases have been people who traveled internationally.