A man has died amid an outbreak of influenza at Toronto's largest homeless shelter as the city scrambles to expand its overcrowded facilities for those living on the street.

Associate medical officer of health Allison Chris confirmed to The Globe and Mail on Wednesday that public-health officials have been investigating an influenza outbreak since Sunday on the "long-term stay" floor of the Seaton House homeless shelter, near Jarvis and Gerrard Streets.

Seaton House informed Toronto Public Health on Wednesday morning that a man staying at the shelter and suffering from "respiratory symptoms" had died, Dr. Chris said. Whether he actually had influenza has not been confirmed and she could not say the victim's age.

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About 23 of the approximately 100 residents on the shelter's fourth floor – many of whom are older than 55 and suffer from mental and physical health problems – have been sick with respiratory symptoms since Sunday, Dr. Chris said. Seven of them had cases so severe they went to hospital.

But for now, Dr. Chris said, the situation at the shelter appears not to be worsening: "Fortunately it seems that we're not seeing more cases at this point."

Special precautions have been taken at the shelter since Sunday. Warning signs have been put up advising residents and staff to wash their hands frequently and cough into their sleeves. Staff who deal directly with sick residents are being advised to wear masks and goggles. And extra disinfectant cleaning is being done.

Local city councillor Kristyn Wong-Tam said she had been told by shelter officials that five of the men taken to hospital were in the intensive-care unit.

She warned that if more outbreaks occur, especially in one of the city's new, crowded temporary warming centres, or in one of the city's mostly church-run Out of the Cold programs for the homeless, the problem could get out of hand quickly.

"I don't believe that we can handle this if it spreads," Ms. Wong-Tam said.

She said activists and front-line workers have been warning city hall for years that the city needed more shelter beds and more health care in its shelters. Just Tuesday, the province of Ontario announced a pilot project to offer more health services in a handful of Toronto shelters.

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On Wednesday, activists with the Ontario Coalition Against Poverty rallied at City Hall to decry crowded conditions and demand more shelter beds.

It is not the first disease outbreak at Seaton House, which just last year emerged from a 19-month outbreak of the bacterial infection strep.

The massive and aging shelter, which can house more than 500 people, has long been slated to be torn down and redeveloped, forcing the city to scramble to replace its capacity elsewhere.

Cathy Crowe, a nurse and long-time advocate for the homeless, said the influenza outbreak underscores the dangers in the city's failure to live up to its own shelter crowding standard, which is to cap its shelters at 90 per cent of their capacity.

"When you have the crowding, it is easier for something like that to spread," Ms. Crowe said.

Jo Connelly, executive director of the Inner City Family Health Team, which provides health services at Seaton House, said her staff, shelter workers and other health workers were trying very hard to deal with what she described as a "very virulent" outbreak.

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She feared there could be more deaths among the men sent to hospital: "We're not sure how many of them are going to make it. It's that serious."

She said one factor at the crowded shelter may have been the influx of homeless people from the street in the current crisis into beds normally reserved for Seaton House's long-term residents, potentially exposing both groups to new illnesses from each other.

A spokesman for John Tory said the mayor is aware of the outbreak and is being updated on the situation.

"The loss of any life is tragic and our condolences go out to this man, his family and friends," spokesman Don Peat said. "Influenza outbreaks aren't unusual at this time of year and we have been informed the city is seeing a number of influenza outbreaks, including in a number of long-term care homes."

Word of the outbreak comes after a shelter-capacity crisis forced city officials to scramble to find new beds as temperatures plummeted in late December, opening a convention centre at Exhibition Place and later the Canadian military's Moss Park Armoury as temporary emergency shelters.

After supporting plans to add a smaller number of new shelter beds last December, Mr. Tory has since called for more investment in the shelter system as the crisis worsened. On Tuesday, his budget chief, councillor Gary Crawford, and the city's budget committee approved a motion to add funding for 1,000 new shelter beds over three years. But activists argue that the plan does not move fast enough.