Health officials have issued a warning on an outbreak of mumps that has already infected three people in Toronto and could hit hundreds more, the city's public health agency said on Wednesday.

The three confirmed cases occurred after two university students returned to Toronto from the east coast city of Halifax, Nova Scotia, and passed it to one of their friends. That person then unknowingly exposed about 300 others to the virus at a busy downtown Toronto bar last week, Toronto Public Health officials said.

The health agency has issued a warning for those people to be on the lookout for signs and symptoms of the disease.

A serious mumps outbreak in Eastern Canada has prompted health officials there to look into plans for a vaccination program.

The mumps is not usually a serious illness, but it can cause meningitis, hearing loss and orchitis (inflammation of the testicles). Women who get the illness in the first three months of pregnancy can also miscarry.

The highly contagious disease has previously broken out in Eastern Canada and the U.S. Midwest.

Canada's outbreak began in Nova Scotia in February where so far 222 people have been infected. Overall, nine cases have been confirmed in Ontario.

The mumps virus is spread through saliva by sharing drinks, food, cigarettes, kissing or by coughing and sneezing.

Symptoms include swelling and pain in the salivary glands, fever, headache, muscle aches and pains, fatigue and loss of appetite.

Most of the recent cases have been among university students who are more susceptible to contracting it.

"Students typically live in residence, they fraternize more and they might share drinks more," said Dr. Vinita Dubey, associate medical officer of health for Toronto Public Health.