Quarantine at two universities in Los Angeles has affected more than 200 students and employees who may have been exposed to measles and either have not been vaccinated or can not check if they are immunized.
The order issued in connection with the University of California and the State University of California comes after the number of measles cases in the country reached a 25-year high. The order requires people to stay at home, avoid contact with other people and notify authorities if they develop symptoms of measles.
The virus is highly contagious, spreading through coughing and sneezing.
"A man with a confirmed case of measles can expose thousands of people to measles," said Dr Barbara Ferrer, director of public health department at a press conference on Thursday.
Los Angeles County Public Health Officials issued quarantine from 24 to 48 hours until evidence of immunity has been established. Some people may need quarantine for up to one week.
Measles in the United States have climbed to their highest level for the past 25 years, bringing together 700 cases this year as a result of the revival due mainly to disinformation that turns parents into vaccines. Approximately three-quarters of this year's disease was in New York state.
A Los Angeles-based university student in Los Angeles, who was diagnosed with measles, may have exposed 500 people to the University of Mercy in early April, according to a statement from the school.
Since Thursday afternoon, 79 of these students and teachers have not provided medical records showing that they are immune to measles, the university said.
"Please be assured that we have the necessary resources for prevention and treatment and that we work very closely with local public health officials on this issue," the UCLA Chancellor said in a statement.
Meanwhile, in Cal State, a person infected with measles, attends a library and probably meets hundreds of employees, some of whom are students. One hundred and fifty-six of them could not provide their immunization files from Thursday afternoon, according to a statement by Cal State.
Health officials have said that there is currently "no current risk associated with measles in the library," officials said.
A small epidemic of measles broke out in Los Angeles County, including five confirmed cases involving travel abroad. Since Thursday, the state has registered 38 cases of measles; Last year there were 11 at the same time, said Dr. Karen Smith, director of the California Department of Public Health.
The state usually sees less than two dozen cases a year, she said.
This year, California cases cover 11 areas and affect patients from the age of 5 to 55 years.
More than 76% of patients were not vaccinated or did not receive the recommended two doses of vaccine, Smith said. Fourteen of those infected have traveled abroad to countries like the Philippines, Thailand, India and Ukraine.
Measles in most people cause fever, runny nose, cough and rash all over the body. However, few of the infected can have complications such as pneumonia and dangerous swelling of the brain.
Centers for Disease Control and Prevention recommend the vaccine for all over one year, except for people who have had the disease as children. Those who have had measles are immunized.
The vaccine, which became available in the 1960s, is considered safe and effective, and so the measles is declared to be all but eliminated in the United States in 2000.
The Associated Press writer John Antchaq participated in this report.
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Christopher Webber, Associated Press