The number of confirmed cases among migrant workers at a St. Thomas-area greenhouse operation has risen to 21, local health officials say.

The first case involving a worker at Ontario Plants Propagation was reported early last week, and an outbreak was declared at the facility on Thursday, according to the Middlesex-London Health Unit (MLHU).

The positive diagnosis led to additional testing involving close contacts and other workers.

By Friday, the health unit said eight cases had been confirmed at the facility involving migrant workers.

That number grew by 11 on Saturday and one on Sunday after the health unit received additional test results.

One case was also confirmed by Southwestern Public Health (SWPH) involving a worker who resides in St. Thomas, said a SWPH spokesperson.

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A total of 74 people have been tested at the farm by MLHU, with 11 tests still awaiting results, said Dr. Chris Mackie, medical officer of health for London and Middlesex, on Monday.

“It’s a significant number of the farm workers there,” Mackie said.

“We haven’t had any significant, severe outcomes in that group.