The Middlesex-London Health Unit has declared a COVID-19 outbreak at an apartment complex in the city's northeast, where almost 50 people have tested positive for the virus.

Between the two buildings, at 112 and 114 Arbor Glen Crescent, 46 people have tested positive for COVID-19, including three staff members.

"The health unit was notified of an initial case who lives in one of the buildings on December 11th and made the decision to declare an outbreak after being notified of 19 cases linked to Maple Ridge on the Parc within the last week," public health said in a statement.

"Health unit case investigators continue to follow up with staff and residents who have tested positive to provide advice and support in navigating the situation. Public health inspectors will also visit the apartment complex today to identify and better understand any practices, events or environmental factors that could have allowed the virus to spread."

The outbreak was declared as the region posted 100 new cases of the virus and another death.

The two buildings are owned by Boardwalk Property Management and have 259 units between them, said Boyd Belisle, the company's director of community corporate culture.

"Right now we are following all the advice that's being given to us by public health for how we care for the staff and residents of the building," Belisle said.

"The health and safety of our staff and residents is always top of mind and we're really grateful that we have the health authorities that can support us."

Health officials say they don't believe the building itself is to blame for the outbreak.

"It has always come down to people grouping together, sometimes that happens in laundry rooms and elevators, sometimes it happens in living rooms and dining rooms," Summers said.

The health unit is asking those who live and work in the buildings to monitor themselves for COVID-19 symptoms and to get tested if any develop. Two-thirds of the outbreak are in one of the buildings, with the remainder of cases in the other.

"The declaration of a COVID-19 outbreak is concerning, especially when it is related to someone's home. Our team is working closely with building management to determine transmission sources and reduce the potential for any further spread," said Dr. Alex Summers, the health unit's associate medical officer of health.

"Whether you live in an apartment building or a single-family home our advice is the same: limit interactions to only those who are part of your household, maintain two metres physical distance from others, and wear a mask in all enclosed spaces, including elevators, laundry rooms and common areas."