Northwest Arkansas' mumps outbreak is the state's largest in at least two decades and is one of the bigger outbreaks in the country in recent years, state officials said.
The Arkansas Health Department counted 520 confirmed or strongly suspected cases of the virus in Springdale, Rogers and Bentonville as of late Thursday. Dr. Dirk Haselow, an epidemiologist with the department, said he expects the number to keep rising for some time.
"Two weeks ago, I would have been much more confident that this outbreak was dampening," he said. "Right now it looks like it's taking another step up."
Haselow said the state before this outbreak typically saw four or so cases a year of the disease. Mumps often causes flu-like aches and fever along with swollen salivary glands around the face, but rarely leads to more serious ailments. There's no treatment specific to the virus, so people who catch it must wait it out.
The state's data doesn't go back more than about 20 years, making it difficult to know for sure when Arkansas last had so many mumps cases, Haselow said. The outbreak is an unusual spike in mumps cases for Arkansas since the vaccine was developed in the 1960s. The vaccine had reduced the number of cases nationwide, from hundreds of thousands each year to a couple thousand or fewer in each of the past five years, officials have said.
Two doses of the vaccine generally protect 88 percent of the people who receive it from any symptoms, according to the federal Centers for Disease Control and Prevention. People who fall into the 12 percent often experience shorter and less severe symptoms even if they catch the virus, Haselow has said, but they can still spread it, as can people who aren't vaccinated.
The CDC tracked a 2014 outbreak in Ohio that affected more than 400 people, and another around 2010 in Guam that affected about 500 people. In 2006, an outbreak that spread over several Midwestern states and college campuses eventually reached more than 6,000 people, according to the CDC.
Arkansas' outbreak seems to have been sparked by another in Iowa in the past year or so, officials say. Health officials there counted almost 600 cases from January to August, according to the Iowa Center for Acute Disease Epidemiology.
Like an ember flying away from a fire, a traveler chaperoning several Northwest Arkansas children as they flew home in early August seems to have carried the virus to Springdale, Haselow said. It spread within a single family, then appears to have spread to their church before reaching several public schools.
The first schools affected grouped around U.S. 412 in eastern Springdale, according to the Health Department. The cluster of schools then spread through town westward to Tontitown. Rogers schools were affected next, mostly around U.S. 71B. At least one probable case was found at Bentonville's Washington Junior High School earlier this month.
Where Iowa's mumps came from is less clear, said Dr. Patricia Quinlisk, Iowa's state epidemiologist. The state's outbreak centered on the University of Iowa, where students and other residents often travel to and from other states, athletic events and other colleges.
The virus can be spread by coughing, sneezing and kissing and spreads more readily in places where people live close together, which can make campuses particularly vulnerable. Quinlisk said the primary outbreak seems to have wound down by early this year, partly thanks to third doses of the vaccine for thousands of students.
The mumps outbreak is small compared with the number of influenza cases every year. The CDC reports about 4,600 people died from the flu in 2014, its latest year available, and tens of thousands were hospitalized.
"If you compared all the illnesses caused by diseases prevented by childhood vaccinations, they wouldn't add up anywhere near to the amount of illnesses caused by the flu," Haselow said.
Metro on 10/15/2016