MONTREAL -- Two busloads of protesters who descended on Montreal's Olympic Stadium last Sunday to protest ongoing COVID-19 restrictions may have, in the process, been exposed to the virus.

The health authority for the Quebec Chaudiere-Appalaches region near Quebec City said Friday that some passengers on a bus that was used to carry people to the May 1 demonstration tested positive for the virus.

"The Public Health Department invites those concerned to get tested and to isolate themselves if necessary in case of symptoms," the CISSS de Chaudiere-Appalaches said in a news release.

A spokesperson said the public callout was necessary in this case, because there hasn't been total cooperation from those involved.

"We are having some difficulties in the investigations," said spokesperson Maryse Rodrigue. "Some people are not cooperating much."

Organizers in the Beauce region arranged the bus that departed in the Saint-Nicolas district of Levis, and took 48 people in two buses to the protest, the CISSS said.

Only a small handful are known to have the virus so far, Rodrigue said.

"I can confirm that there are less than five confirmed positive people who were bus passengers," she said.

Usually, contact tracing would be done without a mass invite for testing, but in this case the normal procedures weren't working well, she said.

"It is rare that we make an appeal to the population, but in this situation, it was necessary," she said.

Montreal police handed out 28 infraction tickets to those not following health guidelines during the protest.