A flu outbreak that has killed at least one person at Toronto's Seaton House has spread to another level, city staff say.

The illness had been contained to the fourth floor of the homeless shelter, but it is now afflicting several patients on the third floor.

Patricia Anderson, a manager with the city's homelessness services, says three people on the third floor of Seaton House are currently displaying flu-like symptoms.

"There's a lot of flu in the wider community this year, so there's no surprise we are seeing it in the shelter community as well," she told CBC Toronto.

Healthcare professionals said earlier that this year's flu season could be particularly bad because two strains of the infection that are particularly prominent this season are not covered by the vaccine given out by the province.

'Infection control measures' to be implemented

Staff at Seaton House are now working with Toronto Public Health officials to implement strict "infection control measures" at the facility, Anderson explained.

Since the outbreak was originally declared last Sunday, a patient died from the virus on Wednesday and 11 people have been hospitalized.

The shelter is the largest for homeless men, with more than 500 beds.

Anderson said that the worst of the outbreak on the fourth floor of the shelter — a "long-stay" floor where residents generally live for an extended period — is starting to wane.