California public health officials have confirmed three more cases of measles in an outbreak that began in late December, bringing to 113 the total number of people believed to have been infected in the state.
Health officials in Arizona, where seven cases of measles have been documented, said the outbreak would likely be considered over in that state if no further infections were reported over the weekend.
Across the United States, more than 150 people have been diagnosed with measles, many of them linked to an outbreak that authorities believe began when an infected person from out of the country visited Disneyland in late December.
The California Department of Public Health said 39 of the 113 people who contracted measles in the state were believed to have been exposed while visiting Disneyland. An additional 34 had contacts with those people in a household or community setting.
Forty cases stemmed from an unknown source of exposure, the department said.
Earlier this week, health officials warned tens of thousands of commuters on San Francisco's Bay Area Rapid Transit system that they may have been exposed to measles after an infectious LinkedIn worker rode the train to and from work for three days.
That rider, who also spent time at a San Francisco restaurant and bar, represented the first case of measles confirmed in Contra Costa County.
In Arizona, Will Humble, the state's director of health services, said the outbreak appeared to be largely winding down in that state because no "third-generation" cases had yet surfaced.
"Measles can take up to 21 days to develop in a person who has been exposed to the disease, so we’re not out of the woods quite yet ... but if we don’t get any new cases by Valentine’s Day, this outbreak is likely over for Arizona," Humble said in a message on the health department's website.
The measles outbreak has renewed a debate over the so-called anti-vaccination movement, in which fears about potential side effects of vaccines, fueled by now-debunked research suggesting a link to autism, have prompted a small minority of parents to refuse inoculations for their children.
Some parents also opt not to have their children vaccinated for religious or other reasons.
Measles was declared eliminated in the United States in 2000 after decades of intensive childhood vaccine efforts. But in 2014 the country had its highest number of cases in two decades.