Legionella bacteria found at London's Victoria hospital, officials say

Testing of Victoria Hospital's cooling towers has returned positive results for legionella bacteria as local health officials investigate an ongoing Legionnaires' disease outbreak in the city, according to officials at London Health Sciences Centre (LHSC). 

LHSC officials say two samples were taken from the hospital's cooling towers and air-conditioning systems on July 16 and 17.

It followed confirmation from the Middlesex-London Health Unit (MLHU) that the Victoria campus fell within a six-kilometre radius where most cases in the outbreak had been found.

In a statement on Wednesday, southwestern Ontario's largest hospital network revealed that the cooling tower samples came back positive for legionella bacteria on an initial screening test.

"More testing is now underway to find out if it matches the strain causing the community outbreak," the statement said. "Those results will take approximately three weeks. We want to be clear: this does not mean Victoria Hospital is the source of the community outbreak."

LHSC said the risk to patients, staff and visitors remains very low, but individuals who are older, have lung problems or are immunocompromised (have a weak immune system) are at greater risk of serious infection.

The outbreak, declared on July 8, has impacted at least 69 people, according to the latest numbers from the MLHU. Two people have since died, and source of the outbreak has not yet been determined.

In an interview, Dr, Nadim Khalil, site lead of infection prevention and control at Children's Hospital, said no hospital-acquired cases had presented to LHSC.

"The public health unit has been testing different samples to see what could be the source of it, and because of our location at Victoria Hospital, we got tested. We have sent samples from our University Hospital as well, which is going to be much more lower-risk," he said.

He added that cooling towers are, "more to help evaporate some of the temperature that's in the building, but not circulate into the air conditioning system."

Legionnaires' disease is caused by legionella bacteria, naturally found in water sources. If conditions are right, it can contaminate hot tubs, cooling towers, hot water tanks, large plumbing systems or parts of air-conditioning systems. 

Legionella is not transmitted from person to person. If the bacteria are aerosolized or misted into the air (via wind or fans), people may inhale the bacteria and become unwell. Most people exposed to legionella don't get ill, but some may experience Pontiac fever, a mild, flu-like illness that commonly resolves itself.

"The challenging thing for us is the cooling towers have to be present to help cool the building, especially during summer, (but) the waters can be a bit stagnant in it because it's not circulating with the rest of the building," Khalil said.

"We do have our policies to get the water tested per provincial guidelines as well as treatment. We treat the water twice a year. When we did hear about the outbreak, we treated the water an extra time."

Khalil says LHSC treated the water a fourth time to be safe, but says the results came back positive, prompting a chemical cleaning of the towers, followed by a thorough systematic clean.

One challenge, he says, is that legionella can be slow to develop — upwards of two weeks on an agar plate.

"So they do additional DNA amplification, what we call PCR, to help see if there's any residual bacteria, and that's what came back positive. What that means is still unclear," he said.

"We do know a lot of water, if it's going to be tested, can be positive, and we do know, talking to the health unit, almost 80 per cent of samples they've had have tested positive."

Last week, health unit officials told CBC News that tests of several dozen systems within the six-kilometre radius came back positive for legionella, making pinpointing the outbreak's source a challenge.