SEATTLE — Measles, declared eliminated as a major public health threat in the United States almost 20 years ago, has re-emerged this winter in the Pacific Northwest and other states where parents have relatively broad leeway over whether to vaccinate their children.

Seventy-nine cases of measles have been reported by the Centers for Disease Control and Prevention since the start of this year. Fifty cases of the highly contagious disease were in Washington State.

An outbreak of measles has also occurred in the Orthodox Jewish community in Brooklyn, where 64 confirmed cases of measles were reported, mostly late last year. That outbreak began, the C.D.C. said, when a child who had not had a measles vaccination caught the virus on a visit to Israel, where a large outbreak of the disease was occurring.

But no place has been hit harder since January than Clark County, Wash., a fast-growing corner of the metropolitan area near Portland, Ore. Clark County health officials declared a medical emergency last month, and say they have seen 49 cases — most of them in children under the age of 10.