SPRINGDALE, Ark. — The number of mumps cases in northwest Arkansas ballooned Tuesday with 14 confirmed cases and another 59 suspected cases.

The mumps outbreak is by far the state’s largest cluster since 2010, when five cases of the viral infection were confirmed.

This year’s outbreak is centered in northwest Arkansas, where the opt-out rate for vaccinations far exceeds any other area of the state, according to Arkansas Department of Health data. State law allows parents to claim medical, religious or philosophical exemptions from school vaccination requirements.

The cases have been found only in Springdale, which straddles both Washington and Benton counties. Washington County had 649 vaccine exemptions for the 2015-2016 school year, and Benton County had the state’s highest number of exemptions at 1,044, health department spokeswoman Meg Mirivel said.

Arkansas’ most populous county, Pulaski County, had 349 vaccine exemptions last school year.

Health department officials don’t know why the exemption rate is so much higher in northwest Arkansas “but it seems to be in line with national studies that show vaccine refusers are likely to be better educated with a high household income,” Mirivel said. Northwest Arkansas is home to several Fortune 500 companies and has some of the highest per capita incomes in the state, according to Census data.

Mumps is a viral infection that causes swelling in the salivary glands and cheeks. Symptoms may also include headaches, fatigue, muscle aches and low-grade fevers, and those afflicted in Springdale include both vaccinated and unvaccinated people, Mirivel said.

The suspected cases include 27 Springdale students and two staff members from 14 schools, KHOG-TV reported. Eleven students with exemptions for the mumps, measles and rubella vaccine must stay home for 26 days, the maximum incubation period for mumps, officials said.