VANCOUVER, Wash. — The number of confirmed measles cases near Portland grew from 25 to 30 on Friday, with nine additional cases suspected — an outbreak boosted by lower-than-normal vaccination rates in what's been identified as an anti-vaccination U.S. "hot spot."
Public health officials in southwest Washington, just across the Columbia River from Portland, Oregon, said people may have been exposed to the dangerous disease at more than three dozen locations , including Portland International Airport, a Portland Trail Blazers game, an Amazon Locker location and stores such as Costco and Ikea.
Twenty-six of the confirmed patients had not been vaccinated against measles and the vaccination status of four others who were infected is unknown. One person has been hospitalized.
Most of the cases involved children younger than 10, the Clark County Public Health Department said in a statement. One adult is infected and the rest are teenagers.
Washington Gov. Jay Inslee, a Democrat, declared a statewide public health emergency for his state on Friday and authorities in neighboring Oregon and Idaho have issued warnings to residents.
Inslee said the number of cases "creates an extreme public health risk that may quickly spread to other counties."
Clark County, which includes the Portland bedroom community of Vancouver, Washington, has a measles vaccination rate of 78 percent, well below the 92 to 94 percent rate required for so-called "herd immunity," said Marissa Armstrong, the department's spokeswoman.
Herd immunity happens when unvaccinated individuals are protected from infection because almost everyone around them has been vaccinated and is immune to a disease.
The measles vaccination rate for 2-year-olds in Multnomah County, home to Portland, was 87 percent in 2017, according to state data. The measles vaccine consists of two shots, one given by age 2 and the second usually between ages 4 and 6.
Data on Portland's vaccination rate for both shots wasn't immediately available.
Two doses of the vaccine in childhood are 97 percent effective and provide lifetime immunity. One dose is about 93 percent effective.
Both Washington and Oregon allow vaccine exemptions for personal and philosophical reasons. Armstrong said the vaccine exemption rate in Clark County for non-medical reasons was high, at 7.5 percent.
People who have the measles can spread the disease for several weeks before they show symptoms.
The virus, spread by coughing or sneezing, can remain in the air for up to two hours in an isolated space. Ninety percent of people exposed to measles who have not been vaccinated will get it, public health officials said.
Every time an unvaccinated person who's been exposed to measles goes out in public, "it starts that clock over again," Armstrong said. "That's the fear."
Earlier this week, authorities were successful in identifying several people who had been exposed but were not sick yet. Those people stayed home and later got ill, Armstrong said.
"We're taking that as a win. That's how we're going to be able to slow this down is keeping these people out of a public setting," she said. "People are helping us and staying home."
Officials still are not sure where the outbreak began.
The first known patient sought medical care on Dec. 31, but it is unknown if other people may have gotten sick before that and did not seek treatment.
Those who may have been exposed should watch for early symptoms of fever and malaise and then a rash starting on the head and moving down the body. Serious complications such pneumonia and brain infections can arise from the disease in some cases.
People who think they may have the measles should contact their health care provider before visiting to avoid exposing others.