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Fear over coronavirus is leading to cancellation of events in Canada and the United States, but a virology expert says there's very low risk to anyone who may attend the upcoming St. Patrick's Day street party in Waterloo.

Every year, thousands of people gather in what city officials call an unsanctioned street party to mark St. Patrick's Day. Last year, more than 30,000 people attended.

But mass events are being cancelled in British Columbia and California, while Italy has imposed a nationwide lockdown.

Waterloo region has had a single case of COVID-19 so far, but public health says the virus is not circulating in the community.

That means risk of contracting it at a massive gathering is very, very low, according to virology expert Stephanie DeWitte-Orr.

Dewitte-Orr is an associate professor with the health sciences and biology department at Wilfrid Laurier University.

"Anytime you're in a large group of people, you're at the risk of catching infectious diseases depending on what is circulating in the community at that time," she said. "There's been a number of scientific conferences I know of that have been cancelled in California, but it's possibly circulating within communities there so that makes sense."

On Tuesday, the county where the San Jose Sharks' home arena is located banned large gatherings of more than 1,000. It means the team could play in an empty arena, neutral site or at the opposing team's venue.

The ban takes effect Wednesday at midnight PT. Santa Clara County had just under 50 cases earlier in the week.

"Right now in Waterloo, there's not a community circulating level of the virus. So, right now, it doesn't make sense to limit group events," DeWitte-Orr said.

But, she said, large gatherings bring the risk of other respiratory infections such as the flu.

"You're putting yourself at a higher risk when you're in a high density environment like that," she said. "Any time someone coughed or sneezed, any time they aerosolised their saliva or their mucus, there'd be virus in those bodily fluids that could be spread."

She said there isn't much you can do to avoid viruses in high-density crowds, short of wearing a respirator.

"For flu, its [reach is] up to two metres," she said. "It can land on you. You could breathe it in."

City officials in touch with public health

Waterloo Mayor Dave Jaworsky says they are keeping an eye on the situation.

"We remain in close communication with public health on this evolving situation," he said in a statement. "I must note that we already advise people that large street gatherings are illegal and unsafe, and people should stay away."

The Region of Waterloo's Public Health Services called the event illegal and dangerous, saying they don't recommend people attend.

"If people are planning to go, we would suggest that they practice infection protection measures to avoid the spread of germs," acting medical officer of health Hsiu-Li Wang said. "These include washing their hands often, avoiding contact with people who are sick staying home if you feel sick, covering your cough or sneeze with your sleeve and avoid sharing drinks and vapes."

Wang added public health will continue to work to address the issues associated with the party.

St. Patrick's Day is on March 17.