Alisha Jucevic for The New York Times

The measles outbreak continues to spread in the United States, surpassing 700 cases this year, federal health officials said on Monday. The virus has now been found in 22 states.

More than 500 of the 704 cases recorded as of last Friday were in people who had not been vaccinated, the Centers for Disease Control and Prevention reported. Sixty-six people have been hospitalized.

About 400 of the cases have been found in New York City and its suburbs, mostly in Orthodox Jewish communities. That outbreak has spread to Detroit.

Los Angeles is now experiencing a fast-growing outbreak, and hundreds of university students who are thought to have been exposed and cannot prove that they have had their shots have been asked to quarantine themselves at home.

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Last Wednesday, the C.D.C. said the number of cases had surpassed the previous high of 667, set in 2014. This year’s outbreak is the largest since the disease was declared eliminated in the United States in 2000. In 1994, there were 963 cases.

Elimination in 2000 meant measles virus was no longer circulating in the United States, as it presumably had since European settlers first brought it to this hemisphere in the 15th or 16th century. Each year after 2000, a few cases arrived from overseas, either in immigrants or in returning tourists, but each outbreak was snuffed out.

More than 94 percent of American parents vaccinate their children against measles and other diseases, Dr. Robert Redfield, director of the C.D.C., said on Monday.

His agency “is working to reach the small percentage of vaccine-hesitant individuals,” he said. “Vaccines are safe and do not cause autism.”

About 100,000 children in this country under age 2 have not been vaccinated, he said, meaning they are vulnerable in this outbreak.

Some infants are not immunized because their parents avoid vaccination. Others cannot be protected either because they are allergic to components of the vaccine or are, for example, taking cancer or organ-transplant medications that suppress their immune systems.

“We must join together as a nation to once again eliminate measles,” Dr. Redfield said.

This year’s widespread outbreak was sparked by people infected with measles who have come into this country since last year, the C.D.C. said. The measles strains detected were most frequently from Ukraine, Israel and the Philippines.

[Get answers to common questions about the measles outbreak.]

Communities have begun to take extraordinary measures to slow the infection rate and crack down on resistance to immunization.

New York City’s Mayor Bill de Blasio declared a state of emergency and threatened residents of four Brooklyn ZIP codes with $1,000 fines if they refused to vaccinate. City officials closed a yeshiva preschool for violating vaccination orders.

Rockland County, N.Y., the…