TORONTO -- Peel Region's interim medical officer of health is apologizing Thursday night after sending the wrong COVID-19 test results to more than a dozen residents.

In a news release, Peel Public Health (PPH) says they accidentally mailed letters to 16 residents that informed them that they tested negative for the virus. In fact, PPH says the residents have the virus.

"I know the relief those residents felt for a few moments has sadly been transformed into feelings of fear and uncertainty," Lawrence Loh said in a statement. "Our team is working quickly to notify these residents and make sure they have what they need to manage this difficult situation."

PPH says the letters were mailed on Tuesday and Wednesday.

Following an investigation, PPH says they found that several positive test slips were mixed with a batch of negative results.

The error was not noticed until after the letters were mailed, PPH says.

"We have made changes to our process to ensure that this situation does not occur again in the future. On behalf of the Region of Peel, I extend apologies to those residents impacted by this error," Loh said.

As of Thursday morning, there are 362 cases in Peel Region. The region reported its second COVID-19 fatality on Thursday night.

In Ontario, 401 new COVID-19 cases were reported on Thursday, bringing the total to 2,793. The province's death toll stands at 53.