The spread of measles in the Southwest now constitutes the largest single outbreak since the United States declared the disease eliminated in 2000, federal scientists told state officials in a meeting on Monday.

The New York Times obtained a recording of the meeting. Until now, the Centers for Disease Control and Prevention had not publicly described the outbreak in such stark terms.

More measles cases were reported mostly in Orthodox Jewish communities in New York City and New York State in 2019. But health officials regard those as separate outbreaks, because they were fueled by multiple introductions of the virus by international travelers.

C.D.C. officials now view the spread of measles in Texas, Oklahoma and New Mexico as a single outbreak, Dr. Dan Filardo, who leads the agency’s task force for the measles response, told state health officials at the meeting.

“This is the largest outbreak in the U.S. since measles elimination was declared in 2000,” he said. The agency was sending seven additional officials to Texas, epicenter of the escalating crisis, he added.