SEATTLE (NYTIMES) - 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 Centres 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, New York, where 64 confirmed cases of measles were reported, mostly late last year. That outbreak began, the CDC 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, Washington, a metropolitan area near Portland, Oregon. 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.
Clark County has one of the lowest vaccination rates in Washington state. About 78 per cent of the kindergarten through high school population is vaccinated, according to state figures.
Along with other cities mainly in the West - including Seattle, Phoenix, Salt Lake City and Houston - Portland is considered a hot spot for families that opt not to vaccinate for medical, philosophical or religious reasons.
For measles, epidemiologists generally consider the threshold for preventing public measles outbreaks to be a vaccination rate of 93 per cent or higher.
"If you have a population that is unvaccinated, it's like throwing a match into a can of gasoline," said Dr Alan Melnick, Clark County's public health director.
Measles can cause permanent neurological damage, deafness and in relatively rare cases, death. All states allow parents to exempt children from vaccination for medical reasons, and most also allow for a religious exemption, according to the National Conference of State Legislatures.
But 17 states, including Washington, Oregon, Colorado and Texas, allow parents to keep their children from being vaccinated for unspecified personal or philosophical reasons. Some may be connected to a broader anti-vaccination movement, including concerns that vaccines lead to autism, an idea that has been widely debunked.