BANGOR (AP) – Maine’s mumps outbreak is worsening with confirmed or suspected cases in 12 of the state’s 16 counties, health officials say.

The University of Southern Maine made national headlines when scores of students were barred from class. But there have been other outbreaks in public schools, and healthy students who have not received their inoculations have been sent home.

State law allows a vaccination waiver for medical, religious or philosophical reasons, but those students are not allowed to go to school during an outbreak, said Dr. Dora Anne Mills of the Maine Center for Disease Control and Prevention.

“We mandate vaccines for a reason. If there’s an outbreak in the school, students without a vaccine will be excluded,” she said. “Vaccines and isolation are the main strategies for controlling the spread of disease.”

As of last week, there had been 54 suspected cases and 12 laboratory-confirmed cases of mumps in Maine since September.

The age of the sickened ranges from toddlers to the elderly. Counties with either confirmed or suspected cases were Androscoggin, Aroostook, Cumberland, Kennebec, Knox, Lincoln, Penobscot, Sagadahoc, Somerset, Waldo, Washington and York.

Mills said the low number of identified cases in Maine is likely “the tip of the iceberg,” and she expects more cases to surface.

“There are probably a lot of cases we just don’t know about,” she said. Laboratory tests, she added, frequently create false negative results.

Mumps is a virus spread by coughing and sneezing. The most common symptoms are fever, headache and swollen salivary glands under the jaw. It can lead to more severe problems, including meningitis and infertility.