As much of a success as “Avengers: Endgame” is for Marvel Studios, some fans in California may have left a midnight showing of the film with something other than a sense of fulfillment.

California Health officials issued a warning to the public regarding a woman who attended the late-night screening at an AMC Theater in Fullerton, California, on April 25-26 without realizing she had the virus. It is unconfirmed which film the woman in question saw, but that was the date Marvel Studios released its highly anticipated “Avengers: Endgame,” as noted by the LA Times.

The woman, who has remained unnamed, was reportedly at the theater from 11 p.m. to 4 a.m. Aside from the moviegoers, officials also reportedly warned employees at the AMC Theater working at the time of her visit.

The theater wasn’t the only place the woman may have exposed others to measles, either. She reportedly went to her workplace in Santa Ana for several days and the St. Jude Emergency Department in Fullerton in late April. Health officials believe she was infectious from April 23 to May 1 before learning she was sick. When she did discover she had the measles, she chose to quarantine herself in her home in Placentia, California.

She is also the first confirmed case of measles to hit Orange County this year. Her actions could also lead to the second confirmed mass outbreak of measles to hit California.

April saw approximately 1,000 students and staff members from two Los Angeles universities be quarantined at home or on campus from a possible measles outbreak.

movie theater
Pictured is a movie theater audience. Getty Images