In a normal year the city only gets, on average, about 15 cases.
According to Toronto Public Health, all of the cases are linked to Ki Restaurant at 181 Bay Street in the city's financial district.
On Saturday TPH said it was investigating four cases of mumps and that all of those affected were restaurant employees.
On Tuesday the number of confirmed cases jumped to nine: eight cases are employees at the restaurant and the ninth is someone who came into contact with one of those employees.
Three other cases are under investigation: one employee and two restaurant patrons.
According to health authorities the risk to patrons is low "however, as a precaution, if you were at Ki Restaurant at anytime on or between July 7 and July 18, watch for symptoms of mumps which could occur up to and including August 12th."
The symptoms of the virus include swelling and pain on the sides of the cheeks and jaw, fever, headache, muscle aches and pains, fatigue and loss of appetite. Read More