So far this year, health officials in Washington state have recorded more than 341 cases of whooping cough. According to the Washington Department of Health, last year at this time, there were 57 cases.
“At this point we’re about 500 percent increase in the number of pertussis cases this year over last year," said Dr. Scott Lindquist, Washington's epidemiologist for communicable diseases.
The greatest risk is to children younger than a year.
"You can actually die from pertussis when you’re an infant," Lindquist said.
He said his agency strongly recommends pregnant women get a booster of the pertussis vaccine.
While the outbreak is concerning, other years have been worse.
“This is certainly small in comparison to the large outbreak we had in the state in 2012," he said. "We had about 5,000 in 2012.”
The whooping cough outbreak started about a month ago in Walla Walla and Kitsap counties, according to health officials. Since then, the number of cases has grown. Washington’s Clark County is among the most affected.
State health officials said they’ve documented 46 cases there so far this year, though Clark County health officials said that number is even higher. At this time last year there were just 16 cases in the county.
This year, most are in adolescent children. That’s also true in the rest of the state.
Monica Czapla, the communicable disease program manager with the Clark County Health Department, said the increase in whooping cough cases is part of a natural cycle. But she said there are other factors at work.
“A lot of it has to do with declining vaccination rates," she said.
Over time, Czapla said, the vaccine becomes less effective. Most children start receiving a series of vaccines to immunize against whooping cough a few months after they're born.
“But what we’re seeing happening is that the immunity that’s provided by this vaccination series starts to wane over time so that you’re less protected as you get older, which might be why were seeing pertussis disease in sort of the high-school age, adult population," she said.
What Czapla means is that the immunization essentially wears off. By the time kids reach their late teens, she said, it’s time for another vaccine. But it’s not clear how many are getting it, in part because there isn’t a lot of data, she said.
So far this year in Oregon, the number of whooping cough cases is more in line with years past.
Dr. Paul Cieslak, the medical director for the Oregon Immunization Program, said the state’s documented more than 150 cases of whooping cough this year.
“There are some hot spots," he said. "We’ve had little mini-outbreaks in Deschutes County and in Benton County. But overall state wide we’re about average.”
Cieslak said he’s not sure why Clark County’s outbreak isn’t affecting Portland more.
“We have had some high years recently in the Portland area and maybe there’s a little bit more immunity right now, but it's hard to predict who’s going to see rises in cases and when," he said.
Like Washington, Oregon’s highest case count in recent history was in 2012, when state health officials documented more than 900 cases.