TORONTO, ONT. -- A COVID-19 outbreak at an Ontario resort earlier this month was the result of people getting "casual" with public health guidelines, the province's top doctor said Thursday.

Dr. David Williams said a group of out-of-town residents staying at the Deerhurst Resort in Muskoka over the August long weekend ignored physical distancing and social bubble rules.

The Simcoe Muskoka District Health Unit confirmed a group of 30 people attended the resort and a local restaurant that weekend, and 11 of them have subsequently tested positive for COVID-19.

Williams warned that the pandemic is not over and people across the province must continue to be vigilant.

"We're not out of the woods at all," he said. "There are still some people who are being casual. There are still some people who are not following the public health measures."

The local public health unit said none of the people involved had symptoms while they were on the trip, but developed them later.

It also said that one local person who had contact with the group has been asked to self-isolate, but so far there is no evidence of transmission to any area residents.

Williams said these instances can have serious consequences for businesses, which often must be closed until public health units can investigate.

"That's what happens," he said. "That's unfortunate. It means that some people were less than responsible and conscientious in handling things."

Deerhurst Resort said it was able to remain open while local health officials investigated because of its compliance with infection control practices.

"There was no indication that the resort was unsafe for guests and staff nor that closing the resort was helpful," the company said in a statement.

It also said that one employee was deemed to be at risk because of contact with the group, but has subsequently tested negative for the novel coronavirus.