TORONTO (AP) – Toronto health officials on Thursday said Legionnaires’ disease was likely the cause of 16 deaths at a Toronto nursing home and warned that more deaths were possible before the bacteria was fully contained.

Dr. David McKeown, the chief medical officer for Public Health Toronto, said there had been no new deaths since Wednesday, when six more elderly people residing at the Seven Oaks Home for the Aged succumbed to the bacteria.

“We have a lot of sick people in hospital still, so I’m not going to make any more predictions about deaths,” he said.

In all, 70 residents, 13 employees and five visitors to Seven Oaks have been affected by the elusive bacteria and at least 34 of them have been hospitalized.

Though officials had earlier ruled out Legionnaires’ based on preliminary tests, they said cultures taken from autopsies, which took several days to grow, proved positive.

“We’ll continue to look for other possibilities, but we feel pretty confident … we’re dealing with Legionnaires’ disease,” said Dr. Donald Low, chief microbiologist at Mount Sinai Hospital. “Some patients are fragile enough that they may still succumb to this.”

Legionnaires’ disease is a type of pneumonia named after a severe outbreak that killed 29 people at a meeting of the American Legion in Philadelphia in 1976.

McKeown said the bacteria grows best in warm water, such as hot water tanks and large plumbing and air conditioning systems. He said the home’s ventilation system had been shut down and bottled water was brought.

When asked about a recent sewage pipe break at a nearby park, McKeown said investigations were under way as to how the bacteria made its way into the nursing home.

“Our environmental investigation is going to leave no stone unturned,” he said.

Toronto Mayor David Miller also sought to reassure residents and tourists that the outbreak is under control.

“This disease cannot be transferred from person to person,” he told a news briefing. “There is not – and there never was – a threat to the general population of Toronto. This disease is environmental, it is not contagious.”

City officials have been eager to downplay any threat of contagion, after losing an estimated $1 billion in tourism dollars during the SARS outbreak in the spring of 2003, when 44 people died of the respiratory syndrome in Toronto.

Legionnaires’ disease can have symptoms like many other forms of pneumonia, so it can be hard to diagnose at first. It can cause death in 5 percent to 30 percent of cases, according to the U.S. Centers for Disease Control and Prevention. Most cases can be treated successfully with antibiotics, and all residents and workers were being treated with a broad spectrum of antibiotics since the beginning of the outbreak on Sept. 25.

In the United States, an estimated 8,000-18,000 cases occur each year, but only a fraction of these are reported, officials say.

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