A spike in measles cases in California and a cluster of cases in Los Angeles County have prompted local officials to quarantine more than 900 people this week in an effort to contain a possible outbreak of the highly infectious disease.

[Post updated 3:30 pm, Friday, April 26.]

The figure rose dramatically on Friday as authorities revealed that more people may have been in contact with someone who was diagnosed with measles, the LA Times reported.

One student at Cal State Los Angeles and one student at UCLA are reportedly among the six cases of measles identified so far in the county in 2019. Officials at both campuses identified potential exposure at on-campus libraries, and moved to seek proof of immunity or a quarantine for anyone who may have been in those areas at the same time as the infected students.

Since Monday, 127 staff and 71 students were quarantined — asked to stay home, for the most part — at Cal State L.A., and 119 people were quarantined at UCLA, for an initial total of 317, officials at both campuses said in statements. Later that number rose, That number has fallen day to day as people in the groups show proof of immunity, meaning a history of vaccination. More than 500 people overall at UCLA were contacted about potential exposure.

The L.A. County Department of Public Health is heading the effort.

The rise in measles cases nationally and internationally has drawn focus to the anti-vaccination movement, which stems around the discredited notion that vaccinations against infectious diseases early in life cause autism.

At UCLA on Thursday afternoon, one male student said he knew of the potential exposure of measles but that most other students had not; students don’t always check or read their email. He said people in the community have mentioned another building where the infected student was seen but have not heard any official communications about it.

“I’m not sure what’s happening, they mentioned they quarantined some of the people, but at the same time, I’m not sure they got everyone, and not a lot of people are aware of it,” said the student, who asked not to be identified.

“I have an appointment to get checked out,” the student added.

The number of people in quarantine dropped to 82 by Wednesday, UCLA said in its statement. Chancellor Gene Block mentioned two other buildings, Franz Hall and Boelter Hall, as places where the infected student attended classes.

At Cal State L.A., the quarantine applied to student or staff employees who were at the campus library between 11 am and 3pm on April 11, said Robert Lopez, the university’s director of communications. “No building is quarantined,” Lopez said.

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Memo Torres contributed to this report.