TORONTO -- An outbreak of COVID-19 in an apartment tower in Hamilton has nearly doubled in size over the past week, now involving more than 100 cases, and 50 more cases were detected at two other residential buildings on Monday.

Since May 4, the number of confirmed COVID-19 infections tied to a building at 235 Rebecca Street, in the Wilson and Wellington streets area, has grown from 55 cases to 103.

All cases are of the B.1.1.7 variant now dominant in the province and one person tied to the outbreak has died.

Hamilton Mayor Fred Eisenberger told CP24 that paramedics have been going door to door in the 164-unit building over the past two days, offering PCR COVID-19 tests to residents.

“We’re working with the property manager to identify the factors that have been contributing to this outbreak in the apartment complex,” he said.

He said he thought the local public health unit “did everything possible” to stop the spread of the virus in the building, but suggested that adherence to public health measures such as masking or distancing in elevators was partially to blame.

“We’re not laying blame here on this, it could happen very innocently, but the reality is the moment (the coronavirus) gets in there it gets much more complicated and much more difficult to deal with.”

Public health officials said last week that “close contact between apartment residents, and socializing between individuals from different households/units,” was likely to blame for the spread.

He said officials are investigating possible exposures at two other apartment buildings in the city – The Village Apartments at 151 Queen Street North, and the Wellington Place Apartments at 125 Wellington Street North.

“We rely on these property management companies to make sure that they’re doing the right thing and that they’re putting the right protocols in place,” Eisenberger said.

Those outbreaks were confirmed on Monday and so far involve a combined total of 51 cases of the B.1.1.7 variant.

Eisenberger said city staff and the public health unit are working to direct those who are not currently self-isolating in the building to book COVID-19 vaccine appointments.

He said the city will work to provide transportation to vaccine sites for those at the building who need it, but that there is not any plan to send a team directly to the building for vaccination, given the number of cases inside.

Public health officials have documented apartment building outbreaks in North Bay, Ottawa, and Mississauga.   

Research from Spain, South Korea, Hong Kong and Japan has suggested regular apartment ventilation shafts or ducts, even when working properly, can contribute to spread of aerosolized virus particles between units, unbeknownst to the residents inside.

Canadian and provincial public health guidance has so far diminished or omitted the possibility of aerosol transmission of coronavirus, instead emphasizing two metre physical distancing to avoid contact with larger respiratory droplets that cause infection.