As the number of mumps cases in Hawaii reached a new high Thursday, health officials urged adults to get vaccinated if they aren’t already immune, and to stay home if they feel sick so they don’t spread the illness.

So far, 81 cases of the highly contagious respiratory disease have been reported, all but two of them on Oahu. The total is far beyond any annual tally in Health Department records dating back to 1990 — and the year isn’t even half over.

Once a common illness of childhood, mumps largely disappeared after the advent of the vaccine, which was introduced in 1967. Over the past decade, typically fewer than a handful of mumps cases have been reported each year in Hawaii.

Then this year, starting in March, cases began popping up across the island. The tally jumped from 65 to 81 between Tuesday and Thursday, reflecting some results that came in over the long Memorial Day weekend.

“When I look at our map of cases, it really is all over Oahu,” said Dr. Sarah Park, state epidemiologist. “We are talking about a respiratory infection that is four or five times more infectious than the common flu.”

Other states have seen large outbreaks as well. In Arkansas hundreds of people fell ill with mumps last year, and more than 300 new cases have been reported this year. Missouri and Washington also reported more than 300 cases as of May 1, according to the Centers for Disease Control and Prevention. As of April there were 2,570 cases of mumps nationwide.

The trademark symptoms are swollen salivary glands, below the ears, resulting in a tender jaw. It can also cause fever, headache, fatigue and muscle aches. Some people have no symptoms, making it especially easy to spread.

Mumps is usually not a serious illness, and patients typically recover in a few weeks. But occasionally it can cause complications, including meningitis, temporary or permanent deafness, swelling of the brain and even sterility.

None of this year’s cases have led to serious complications or hospitalization, Park said. All patients have recovered or are recovering.

About 40 percent of the patients were adults, according to the Health Department; none of the infected were infants.

The disease is spread through saliva or mucus from the mouth, nose or throat, through coughing, sneezing, talking and sharing items. It has a long incubation period and usually takes 16 to 18 days after infection before the onset of symptoms.

Although Hawaii has a high rate of childhood immunizations, the mumps vaccine is not foolproof, with an estimated 88 percent effectiveness after two doses. It is delivered in combination with the measles and rubella vaccines, known as the MMR vaccine.

According to the Centers for Disease Control and Prevention, 94.7 percent of Hawaii children had at least one dose of the MMR vaccine by 35 months of age. That’s above the national average of 91.9 percent. In Hawaii virtually all schoolchildren receive both doses of the MMR vaccine before being admitted on campus.

The recommendation for a second dose was not made until 1998, Park said. So some adults might be at risk.

On Thursday the Health Department advised adults born in 1957 or later, who have no evidence of immunity to mumps and cannot verify previous vaccination, to get at least one MMR vaccine. It strongly encouraged those with just one documented MMR dose to consider receiving a second dose.

The vaccine resulted in a huge decline in national numbers of mumps cases, from close to 186,000 cases annually before 1967 to just 229 nationwide in 2012. But the number spiked to 5,833 last year.

“Mumps used to be an exclusively childhood disease because everyone got it by the time they were 15 or 20,” said Dr. Marian Melish, hospital infection control officer at Kapiolani Medical Center for Women & Children and a professor at the University of Hawaii medical school. “It was not ever seen in adults.”

“This outbreak is occurring in both children and adults,” Melish said. “It’s occurring in vaccinated people and undervaccinated people and unvaccinated people.”

Some of the outbreaks nationally have been clustered on college campuses.

“Many states have been very heavily impacted this year,” Melish said, adding that they may have caused “multiple importations” to Hawaii given its high rate of visitors.

The strain of mumps circulating in Hawaii does not appear to be out of the ordinary.

“We have sent select specimens off to CDC for sequencing, and they haven’t identified anything unusual about the strain circulating here,” Park said.

While some people who are vaccinated still remain susceptible to the disease, having taken the precaution might help them weather the illness.

“In talking about this with the CDC experts, even if the vaccine is not 100 percent effective, just by having been vaccinated with at least one dose may play a role in ameliorating the severity of the disease if you get infected,” Park said. “Just from seeing our cases, that seems to be playing a factor.”

“Knock on wood, we haven’t heard of any complications from mumps,” she added. “Hopefully, that’s a reflection of the fact that we do have a relatively vaccinated population.”

Park and other physicians urge people to stay home when they feel ill rather than going to work, school or the grocery store.

“If we as a community can get all the sick people to stay home, we would see a dramatic drop in not just mumps, but any other respiratory disease,” Park said.

Dr. Laura DeVilbiss, medical director at Kokua Kalihi Valley, said her clinic has had five cases total so far, two at the start of the outbreak and three in the past week.

“We encourage people to stay home to protect others,” she said. “If they have any swelling, don’t go out in public. It keeps spreading because people don’t realize they have it. They spread it before they get diagnosed.”

“If there is any swelling in the face,” DeVilbiss added, “call the doctor before coming in so you don’t infect everyone in the waiting room.”