The state Department of Health reported eight new cases of mumps Thursday, pushing the total to a milestone of 104 in the largest outbreak in Hawaii in decades.

Although the year is not even half over, the current total far outpaces the previous annual high of 42 cases in 2001, according to state health data that reach back to 1990. Hawaii health officials said they expect the outbreak to continue and are investigating new cases.

“People who are sick need to stay at home,” Dr. Sarah Park, state epidemiologist, said Thursday. “Trying to keep your distance from others when you are sick is really important in trying to slow this down and stop it.”

Once a common childhood disease, mumps was largely wiped out after a vaccine was introduced in 1967, but it has been making a comeback in the last few years in various mainland states.

So far no hospitalizations have been reported among the Hawaii cases. The diagnoses confirmed over the past week involved three adults and five children on Oahu.

Along with the trademark sign of swollen salivary glands, symptoms of the mumps include low fever, fatigue and muscle aches. But some people don’t even know they have it.

The highly contagious viral disease is generally mild in children, but it can cause complications, especially in adults. In rare cases mumps can cause meningitis, temporary or permanent deafness, and swelling of the brain, testicles or ovaries.

The Health Department is calling on families to ensure their kids have received both doses of the mumps vaccine, and urges adults to get vaccinated if they are not already immune. The measles, mumps and rubella vaccine, known as MMR, is 88 percent effective with two doses and 78 percent effective with one dose.

“If you’re an adult or anyone who cannot document having received your MMR, you really need to go in and have one,” Park said Thursday. “And if you do have one, get the second dose, because we know that two doses are better than one. Upping the immunity in our communities would really help.”

“During the hepatitis A outbreak we saw a huge uptick in vaccination,” she added. “With MMR we haven’t heard much in terms of demand or concerns. That’s a challenge. Mumps is not a particularly sexy disease.”

The recommendation for a second MMR dose came in 1998, so many adults may not have had it. People born before 1957 tend to be immune since the disease used to be so prevalent.

Mumps is spread through coughing, sneezing and sharing cups and utensils.

“Many people have no symptoms at all,” said Dr. Marian Melish, infectious disease control officer at Kapiolani Medical Center for Women & Children. “That’s one reason why it can spread.”

Her recommendation: “vaccination and hand-washing,” plus staying at home until you are no longer contagious.

“It’s possible now that school is out, this outbreak will wane a bit, at least the part that is going on in young adults and children,” Melish said in a recent interview. “They’ll be less likely to be together in indoor environments.”

“It’s a highly contagious disease but not a very severe one,” added Melish, a professor of pediatrics, tropical medicine and medical microbiology at the University of Hawaii Medical School. “It’s unlikely to do you any great harm. Only a few people will have complications.”

For more information, visit health.hawaii.gov/docd/department-of-health-­investigating-mumps-cases.