"We typically see about five to six cases per year," Dr. Sarah Scott, who studies diseases for the department, told Phoenix New Times on Thursday. "For 2019 to date we've seen 20 cases."
Twelve of those cases have emerged in just the last four months, Scott said. The disease is affecting children and adults across the county, and the outbreak has resulted in one hospitalization, she said.
Mumps is a contagious disease of the salivary glands that can cause pain, tenderness, and swelling on the face along the jawline. The disease is rarely deadly. But as the county's news release on Thursday warned, complications can be serious, — swollen testicles for males, swollen ovaries for females, and in rare cases, meningitis, decreased fertility, or even deafness.
It's unclear whether Maricopa County's current outbreak is related to cases in other parts of the state this year, but most of the people in the county who got sick hadn't traveled internationally, meaning they were exposed to the disease locally.
"These cases were not exposed somewhere where we know mumps is circulating," said Dr. Rebecca Sunenshine, the medical director for disease control for the department. "That tells us that mumps is circulating in our own community."
In Maricopa County, the rate of kindergartners getting the MMR vaccine is down a full percentage point from the 2015-2016 school year.
That's alarming, she said, because the county's vaccination rates are decreasing, which means more of the public could be at risk. Public health officials often talk about herd immunity, or community immunity, which means that if enough people get vaccinated, it can protect those who can't be vaccinated because they are too young, have compromised immune systems, or for other medical reasons.
Doctors recommend that to protect against mumps, people should get two doses of the MMR (measles, mumps, and rubella) vaccine.
But in Maricopa County, the rate of kindergartners getting the vaccine is down a full percentage point from the 2015-2016 school year. The most recent data, from the 2018-2019 school year, indicates just 92.7 percent of kindergartners are getting immunized.
"Being vaccinated is the best way to protect yourself from getting mumps," Scott said.
Despite health department recommendations, at least one Arizona lawmaker is trying to abolish the vaccination requirement currently in place for students in public schools. Republican Representative John Fillmore of Apache Junction introduced a bill in the state Legislature last week that would make vaccinations "solely the decision of the pupil's parent."
Currently, vaccines are required in kindergarten in Arizona unless a child qualifies for certain medical, religious, or personal belief exemptions.
Scott said the public health department relies on school-mandated immunization to "protect people who are vulnerable and can't be vaccinated."
Fillmore didn't answer calls for comment.
The public health department says now that it's identified the outbreak, the next steps are to notify the public about the importance of immunizations, and to inform doctors, who may not regularly see mumps cases, about how to spot one.
For the public, the doctors said it's important to protect yourself from disease the way you normally would: washing your hands, avoiding sharing food and drinks, and covering coughs and sneezes.
If you think you might have mumps, they said, you should call ahead to your doctor and go in for a cheek swab, blood test, and urine sample.