A mumps outbreak has knocked more than 100 health-care workers in the Halifax area out of commission.

As many as 136 hospital workers are on paid leave and in isolation because they've tested positive for exposure to mumps.

They are among about 550 employees who have been exposed to the disease since the outbreak began in February, the Capital District Health Authority said Monday.

One employee at the Dartmouth General Hospital contracted the disease, and that had a domino effect on the surgical schedule, said a health authority spokesman.

"We had several staff off because of exposure to mumps last week, and because of that, we had to cancel 20 surgeries," said Peter Graham.

"We're back up to regular scheduled surgeries this week, but that could change in another area if another case appears."

Blood tests on all of the district's health-care workers showed 556 of them have been exposed to the mumps.

"We have 136 health care workers who are currently off work right now because they were confirmed to have been exposed to mumps and were not immune," Graham said.

People born from 1970 to 1992 most at risk

A vaccination program to reach as many as 40,000 health-care workers will begin this week.

There have been 222 reported cases of the mumps in Nova Scotia since February.

New cases have also turned up in New Brunswick, P.E.I. and Ontario as students head home for the summer. Health officials said students may be incubating the infection, but the risk of outbreak is low, since the students are not living in close quarters. 

People born between 1970 and 1992 are most at risk. They only got one dose of mumps vaccine, which doesn't reliably protect them. Children now receive two doses.

Before 1970, people gained immunity by getting the mumps.

Canada's national advisory committee on immunization meets in a few weeks and is expected to talk about whether all adults born after 1970 should get a mumps booster.