A student at Saunders Secondary School who tested positive for COVID-19 attended class while sick with the virus, the Middlesex-London Health Unit (MLHU) says.

Those in the same class as the student were told to stay home and to quarantine, according to a statement from the health unit.

"MLHU investigators have determined that the student attended class while they were infectious and are working directly with them to identify their other close contacts," officials said.

The health unit was told about the student late Tuesday night.

"Thames Valley wishes to assure the school community that staff and parents/guardians of all Saunders students were immediately notified. The school will remain open and school buses will operate," the school board said in a statement.

The health unit is working with the student and his or her family and close contacts directly, Medical Officer of Health Dr. Chris Mackie said in a statement.

"We're seeing a very small number of cases being reported in schools and there's been no transmission in these settings to date. That said, we and our school partners will continue to be vigilant."

The age, grade or number of close contacts at the school will not be revealed, officials said.

Also in London, a staff member at Ecole elementaire La Pomeraie, in the southwest, has tested positive, the French-language school board said on its website.

This is the third case of coronavirus in a Thames Valley District School Board school. The school board keeps a running tally of active cases in its schools on a web portal.

"Thames Valley is following all of the health and safety protocols recommended by public health and the Ministry of Education," said Thames Valley Education Director Mark Fisher. "Saunders Secondary School remains a safe place to attend school."

The other two school cases also involved students, one at H. B. Beal Secondary School, the other at Mitchell Hepburn Public School in St. Thomas. Two students doing remote learning have also tested positive.