There have now been 880 measles cases reported in this year’s outbreak, already the largest since 1994 , federal health officials said on Monday.

An additional 41 cases were reported last week, according to the Centers for Disease Control and Prevention. Of those, 30 were in New York State, which is having the country’s most intense outbreak, largely in Orthodox Jewish communities.

Most of those new cases were in New York City, and nine were in suburban Rockland County.

Cases have now been recorded in 24 states.

It is too early to tell whether the outbreak is slowing down, a C.D.C. spokesman said. In New York, transmission of the virus briefly appeared to slow in January, but then sped up in February.