HONOLULU — Hawaii health officials have announced that four new mumps infections are being treated, bringing this year’s total to 27 confirmed cases as of Thursday.

An increase in mumps infections is being seen both nationwide and internationally, officials said.

The new Hawaii cases were reported on Oahu. Previous cases were confirmed in Kaimuki, Waipahu, Kalihi and Waianae, according to news reports.

Health officials say this is the highest number since 2001, when there were 42 reported cases.

The spread of mumps can be prevented by vaccinations, officials said. Those suspected of having mumps or have been diagnosed should avoid exposure to others for nine days after swelling of the salivary glands, one of the symptoms.

“The vaccine is not 100 percent,” state epidemiologist Dr. Sarah Park said. “It’s still the best method of prevention, but it’s not 100 percent. On top of that, it’s the way mumps is spread.”

There is a small number of the population whose immune systems do not respond to the vaccine, Park said.

Health officials said at least 16 cases involved patients under 18 years old, and at least eight schools have notified parents about students getting mumps.