The largest mumps outbreak the United States has seen in a decade or longer also is the worst in years in Washington, and its spread is ongoing in the South Sound.
The local epicenter is in South King County — Auburn has 99 of the outbreak’s reported 178 Washington mumps cases, according to state and county totals released this week.
It is the worst outbreak in Washington in 26 years, a state Department of Health spokesman told the Spokesman-Review in Spokane.
But the virus has turned up throughout the region, including four cases in Fife schools and two in the Puyallup School District since Dec. 9. Eleven cases have been confirmed in Pierce County and five more are being investigated.
So far, Thurston County has no confirmed mumps cases, health officer Dr. Rachel Wood said Friday. “Some school children are being evaluated, but nothing has shown up positive for mumps,” she said.
Health experts said they cannot predict how long the surge of mumps cases will last.
“I wish it would blow over tomorrow. We have no way of knowing,” said Denise Stinson, a nurse epidemologist with the Tacoma-Pierce County Health Department.
With case reports still coming in from state health departments, a federal Centers for Disease Control and Prevention expert said she can’t say whether the total mumps cases in the outbreak — 5,311 as of Dec. 31 — eventually will surpass the 6,584 cases nationally in 2006, the most since doctors in the 1980s recommended two rounds of vaccinations.
The 2006 outbreak was centered in the upper Midwest, with rural areas and college campuses from Minnesota to Missouri taking the hardest hit.
Experts have not found a single underlying factor, said Jannell Routh, a medical epidemiologist with the CDC’s mumps team.
This year’s three outbreaks fit the disease’s general pattern of being spread largely in schools and in colleges, where large populations spend their days in close, repeated contact.
The mumps vaccine generally is about 88 percent effective, instead of conferring total immunity.
That’s a lower rate than the measles vaccine, which usually is administered in the same MMR (measles, mumps and rubella) immunization as the mumps dose. The measles vaccine has a 97 percent effectiveness after two rounds, according to the CDC.
Additionally, mumps can be spread by people who don’t have symptoms of the illness.
“All of those factors combine to make the perfect storm for a mumps outbreak to take hold,” Routh said.
She said the country’s ongoing anti-vaccination movement, which originated with a discredited research paper in a medical journal, doesn’t appear to have played a large role. Most mumps cases in the current outbreak have been among people who were vaccinated twice, as per recommendations.
“No vaccine is 100 percent effective,” she said, “so we do expect vaccine failure from time to time.”
The CDC has not declared a widespread emergency over the current mumps outbreak, although the agency has convened a yearlong study over whether to recommend people get a booster shot of the mumps vaccine during a bad outbreak, Routh said.
For now, its working recommendations are the usual disease-prevention steps: wash hands frequently, cover your mouth when coughing and isolate mumps cases as soon as they’re discovered.
Auburn schools in December sent 300 children without proof of up-to-date mumps vaccinations home for 25 days, per a county health department request.
The Puyallup School District excluded students who are “unvaccinated or under vaccinated” against the disease after a student from Northwood Elementary School came down with mumps.
Thirteen possibly affected students at Northwood will be excluded starting Monday, while seven possibly affected at Edgemont Junior High School will be excluded starting Tuesday.
After unvaccinated or undervaccinated students receive both doses of the MMR vaccine, the district will allow them to return to classes.
In Fife, schools officials told families with unvaccinated or under-vaccinated children that they will have to stay home until are they vaccinated or the danger of contracting the disease has passed.
Although nonfatal in nearly all cases, the disease can have effects that last far beyond the fever, headache and facial swelling that are its most common symptoms. Meningitis, spinal cord inflammation and deafness can result, and people who get mumps after puberty sometimes are rendered sterile.
Children who catch mumps generally are immune for the rest of their lives. That’s why most people born before 1957, in the prevaccine era, are thought to be immune now.
Those who catch it despite going through full immunization generally come down with milder cases, said Nigel Turner, director of the communicable disease division of the Tacoma-Pierce County Health Department.
Although this year’s caseload is higher than local and national officials are used to seeing, the numbers are far diminished from the years before the mumps vaccine was licensed in 1967.
“What we’re seeing now is only a fraction of what we’d be seeing if there wasn’t a high level of vaccination out in the community,” Turner said.
More information about mumps is available at the Tacoma-Pierce County Health Department website, tpchd.org/mumps.