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It's a cruel irony that in a setting where clean hands are critical, the sinks turned out to be the problem.

The design and placement of hand hygiene stations in hospital rooms housing transplant patients was responsible for an outbreak of bacterial infections that left 12 patients dead and two dozen others sickened, Toronto doctors who cracked the mystery behind how the bugs were spreading reveal in a new study.

The outbreak is history, having occurred - without much public attention - between December 2004 and March 2006 at Toronto General Hospital.

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But the infection control specialists who tracked down the source of the multi-drug resistant bug involved in the outbreak believe other hospitals could learn from the tragedy that befell their transplant unit.

"The main reason that we published this is because we thought that this was an important lesson. People need to know this," says Dr. Michael Gardam, senior author of the article, published in the January issue of the journal Infection Control and Hospital Epidemiology.

"The message from this for us was that hand hygiene sinks are obviously really important - and they have to be the right design. And they have to be in the right place. And they can't be splashing."

The bug behind the outbreak was Pseudomonas aeruginosa, a moisture lover. It thrives in drains, where it forms what scientists call biofilms. The rest of us call that slime, sludge or gunk.

Pseudomonas bacteria are everywhere. In fact, the bug would probably be found in most household drains if anyone bothered to check. But no one would. The bacteria pose no threat to healthy people.

But it's a different story for patients who have just received an organ transplant. These patients are on drugs that suppress their immune systems so their body doesn't reject the donor organ and their systems are already weakened by whatever caused the need for the transplant.

In these and other seriously ill hospitalized patients, Pseudomonas can trigger skin, wound or bloodstream infections or pneumonia. And if the bacteria become resistant to antibiotics - as bacteria in hospitals are wont to do - the infections they cause can be challenging to treat.

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"You had to be sick to get the infection. The infection makes you sicker," explains Dr. Gardam, head of infection control for the University Health Network (Toronto General is one of its three hospitals) and director of infectious diseases prevention and control at the Ontario Agency for Health Protection and Promotion.

"And when you've got an organism that is resistant to everything, there's not a lot of treatment we can offer you. That was basically the situation we were in."

When it became apparent transplant patients in the hospital's medical and surgical intensive care unit, transplant step-down unit and transplant ward were becoming infected with a multi-drug resistant strain of Pseudomonas, the infection control team began an intensive investigation to determine how patients and bugs were coming into contact.

Initially the cases were patients who were located near one another, leading infection control to suspect health-care workers were transferring the bugs on their hands. But when other patients started cropping up, it became apparent the answer wasn't that simple.

In all, 36 patients were either infected or colonized with the outbreak strain. (Colonized means a person is carrying the bacteria on the skin or in cavities like the nostrils, but the bacteria isn't causing illness.) Two-thirds of the patients were infected and 17 died. A retrospective review of the deaths concluded the outbreak strain killed five patients and contributed to the deaths of seven others, the article says.

Given Pseudomonas aeruginosa's fondness for moisture, the infection control team began testing sinks. Bacteria were found in some but not others, and in some it was only found intermittently.

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"It was really only when we said: 'OK, we're going to test every single bloody sink multiple times' that we started finding it in some of the sinks. It was never in all of the sinks. It was only ever in some of the sinks," Dr. Gardam says.

And how it was getting from drains to patients wasn't clear. "This was the kind of thing that kept us all up at night," he admits.

The painstaking investigation led to the conclusion that the design of the sinks was responsible.

Each single-patient room in the medical and surgical intensive care unit had its own hand hygiene station. They were located just over a metre from the head of the patient's bed and adjacent to a counter top health-care workers used to prepare medication and sterile dressings for the patient.

The sinks had shallow basins and high, gooseneck spouts that flowed directly into the drain below. Because of that design, the pressure from the spout splashed water out of the drain, spraying nearby surfaces.

If the drain contained Pseudomonas, it meant that using the sink ended up showering the counter top and maybe even the bed with droplets of bacteria-laced water.

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The infection control team proved this using a CSI-like approach. Hospital room surfaces were covered with black paper, a fluorescent gel was injected deep into the drain and someone washed his or her hands.

Using an ultraviolet light in the blacked out room, the investigators saw fluorescent splatter had travelled at least one metre - as far as the head of the bed and onto the preparatory counter. The authors believe smaller droplets probably carried further.

On the strength of that evidence, the hospital took the step of removing the sinks. No new cases were reported after that. New sinks with a different design were installed, with splash guards between the sink and the treatment preparation area. Testing showed the splatter problem had been solved.

Dr. Andrew Simor, an infection control expert at Toronto's Sunnybrook Health Sciences Centre, says the outbreak report identifies two issues of which hospitals should take note.

While single rooms with sinks are ideal for cutting the risk patients will pick up hospital-acquired infections, those sinks shouldn't be located too close to beds or treatment preparation areas.

And the design of sinks is critical. Dr. Simor says hospitals can't prevent biofilms from forming in drains, despite their best efforts. But by limiting the potential for splashing, they can perhaps keep those biofilms where they can't hurt patients.

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"We're always learning," says Dr. Simor, who heads the microbiology department of his hospital.

"And that's why this was an instructive report. Because it does remind us that it's not just as clear cut as having a private room with a sink."

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