Health authorities reported 90 additional cases as of April 11, with outbreaks in New York, Washington, California, New Jersey and Michigan. Those cases were largely linked to travelers returning from countries seeing outbreaks of their own, including Israel, Ukraine and the Philippines.
The disease then spread through populations in which large numbers of people are unvaccinated, the CDC said.
The number of new cases has been climbing each week, according to the agency’s numbers. There were 90 new cases last week, up from 78 the week before.
During the last major outbreak, in 2014, there were 667 cases during the whole year.
This article originally appeared in The New York Times.