At least 17 people now have mumps in an outbreak linked to more than 10 bars in west downtown Toronto.

Dr. Vinita Dubey of Toronto Public Health said Thursday the lab-confirmed cases, up three from the previous day, include two men with the serious complication of painfully swollen testicles.

All those sickened by the highly contagious, virus-triggered infection are between the ages of 18 and 35. Most reported having recently visited bars between Yonge and Dufferin Sts.

“It’s not the bars themselves,” responsible for the spread, Dubey said in an interview. “It’s what people do when they get to a bar.”

That behaviour, she added, could include: sharing glasses, utensils or cigarettes; kissing, coughing in close quarters: and speaking for extended periods in a crowded space.

The mumps virus is found in saliva and respiratory droplets. People can be infected and contagious for a week without knowing it. Symptoms that can last up to 10 days include: swelling and pain in salivary glands in the cheeks and jaw; fever; headache; muscle aches and pains; fatigue; and loss of appetite.

Orchitis — inflammation of the testicles — is the only serious complications seen so far in the Toronto outbreak. Although public health says risk to the general public is “low”, other possible complications include infections of the brain or the lining of the brain; inflamed ovaries; pancreatitis, and hearing loss.

Pregnant women infected during the first three months of pregnancy face an elevated miscarriage risk.

People who think they have mumps should tell their doctor before arriving at a medical office.

Public health should know by the middle of next week if the outbreak continues to grow or if the spread is slowing, Dubey said. Many of those infected had zero or one dose of the vaccine for mumps, measles and rubella.

Most Torontonians born in 1992 and later have been vaccinated twice, as a baby and then between ages 4 and 6, making them less susceptible. Public health normally sees a total of about four mumps cases per year.

One of the city’s biggest drinking days, St. Patrick’s Day, is on March 17.

The last publicized mumps outbreak in Toronto hit in 2011, with most of those cases tied to a sushi eatery in the financial district.

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Outbreaks are frequently seen on sports teams, where water bottles are sometimes shared, and universities.

Manitoba has seen 164 confirmed cases between last Sept. 1 and Feb. 16, most of them at Winnipeg universities.