A mumps outbreak has been steadily growing in Los Angeles County since the beginning of the year.
There have been more than 40 cases of mumps reported in the county and surrounding areas since early January, according to the L.A. County Department of Public Health. Most of those cases are among gay men living on the west side of L.A. and in West Hollywood.
At least one patient was unvaccinated; 12 didn't know if they had been vaccinated.
The outbreak appears to be spreading in large venues like gyms, bars, theaters and nightclubs.
Here are answers to common questions about mumps:
What are the symptoms of mumps?
Mumps is best known for causing puffy cheeks and a swollen jaw; these symptoms are a result of swollen and tender salivary glands under one or both ears, according to the Centers for Disease Control and Prevention. Other common symptoms include fever, headache, muscle pain, fatigue and lack of appetite.
Symptoms typically appear 16 to 18 days after infection, but this period can range from 12 to 25 days after infection, according to the CDC. Some people who get mumps have mild or no symptoms and often don't know they have the disease.
In rare cases, mumps can cause serious complications, including deafness, meningitis or encephalitis, the CDC says.
How is mumps spread?
Mumps is spread through saliva or mucus from the mouth, nose or throat. An infected person can transmit it through kissing or sharing cups, utensils, lipstick or cigarettes.
Who is at risk for mumps?
In the current outbreak, the majority of mumps cases are among gay men, but women and heterosexual men have also been infected.
Mumps has also been known to spread through college campuses and dormitories.
How is mumps prevented?
The CDC recommends that kids get two doses of the MMR vaccine, which protects against measles, mumps and rubella. It recommends getting the first dose at age 12-15 months and the second dose at 4-6 years, before the child enters school.
The mumps component of the shot is the least protective and has been shown to have waning efficacy, according to Michelle Parra, director of immunization at the L.A. County public health department.
The mumps component of the vaccine is about 88 percent effective when an individual gets both doses; one dose is about 78 percent effective, according to the CDC.
I'm an adult and I don't know if I've had two doses of the vaccine. What should I do?
Adults without proof of vaccination should get the two-dose series, the county health department says. Adults who don't know if they've had one or both doses should get fully vaccinated. Parra says there's no health risk associated with getting vaccinated again.
I think I was exposed to mumps. What should I do?
There is "conjecture" that an extra dose of MMR vaccine in those who have been previously vaccinated may limit the duration and size of mumps outbreaks, according to the county health department.
If you are fully vaccinated and think you've been exposed to the mumps, you should consult a doctor. Given the waning efficacy of the mumps component of the vaccine, your provider may consider recommending a booster dose, Parra says.
She notes that the CDC has not yet recommended people get a booster dose, and while the California Department of Public Health has said it could help, it also is not recommending it at this time.