The percentage of injection-drug users from Vancouver's Downtown Eastside neighbourhood found to be carrying a worrisome superbug jumped 150 per cent from 2000 to 2006, a study reveals.

The rise was fuelled by the spread of a worrying strain of methicillin-resistant Staphylococcus aureus, or MRSA, which has been causing soaring rates of community-acquired infections in the United States, researchers from Vancouver Coastal Health and the University of British Columbia say.

Experts called the rapid increase startling and suggested it could be a harbinger of what is in store for the wider population as the drug-resistant bug makes its way through Canadian communities.

"I think what this says is: We've got a genetically very smart micro-organism here," said senior author Dr. Elizabeth Bryce, a medical microbiologist and infection-control specialist with Vancouver General Hospital. "And these [injection-drug users] could be the canaries in the coal mine."

Dr. Andrew Simor, chief microbiologist at Toronto's Sunnybrook Health Centre, agreed.

"This article just documents what's happened in Vancouver, but it also true in other Canadian centres," Simor said, including Calgary, Toronto, Montreal, London, Ont.

The study, published in the February issue of the Journal of Clinical Microbiology, compared MRSA colonization rates over time in injection-drug users, a group known to be at higher risk of both carrying the bacteria and developing infections triggered by it.

Other high-risk groups are residents of First Nations reserves, athletes who play team sports and prison inmates.

Steep rise

Bryce and her colleagues found that in 2006, 18.6 per cent of 300 injection-drug users tested were carrying MRSA, a steep and surprising rise from the 7.4 per cent shown to be "colonized" with the drug-resistant form of the bacteria in 2000.

"This is certainly one of the highest colonization rates I've seen," said Dr. Elizabeth Bancroft, a medical epidemiologist with the public health department of Los Angeles County, which for years has been battling what is now considered an endemic MRSA problem.

Staph bacteria are ubiquitous. Between 25 and 30 per cent of healthy people carry Staph in their nose or on their skin at any given time. Some will go on to develop Staph infections — often boils or skin lesions, but sometimes life-threatening bloodstream infections or pneumonia.

The proportion of people carrying the drug-resistant form of the bacteria is substantially smaller. The U.S. Centers for Disease Control estimate in that country, about one per cent of people are colonized with drug-resistant strains.

MRSA colonization rates haven't been calculated for Canada but "I'm sure it would be even lower," Simor said. (Neither Simor nor Bancroft were involved in the Vancouver study.)

Experts worried

Rather than take comfort in Canada's lower rates, infectious-disease experts in this country are worried. Simor and others believe the MRSA profile here is shifting to become more in line with that of the United States, where invasive MRSA infections are estimated to have caused nearly 19,000 deaths in 2005.

What concerns public health experts on both sides of the border is the spread of MRSA outside the walls of hospitals, where the drug-resistant strains were historically found. The combination of sick people and abundant antibiotic use makes hospitals a fertile breeding ground for MRSA and other superbugs.

But in the last decade or so it has become apparent new strains of MRSA have arisen and are circulating beyond hospitals.

Alarmingly, they were causing infections in healthy people who hadn't been hospitalized and hadn't been on antibiotics — in short, people who previously wouldn't have been considered at risk of developing MRSA infections.

In the U.S., much of the community-acquired disease is caused by a drug-resistant Staph strain known as USA-300.  That is the strain Bryce and her colleagues found so commonly among the Vancouver injection-drug users.

When the initial testing was done in 2000, none of those who were colonized carried the USA-300 strain. Instead, they were colonized with a strain known as USA-500, a strain generally found in hospitals.

Surprising shift

By 2006, only a quarter of the colonized drug users carried USA-500 bacteria. The remaining 75 per cent were carrying the USA-300 strain. Bancroft found the overwhelming shift surprising.

"What was remarkable to me is not only did the rate of people with MRSA just jump up, but almost the entire increase was due to the so-called USA-300 strain coming into this population and then sort of spreading," she said.

While this particular strain most commonly causes skin and soft tissue infections, it can cause severe illnesses. In February 2006, for instance, a previously healthy Scarborough, Ont., teenager died from an MRSA-triggered pneumonia.

"It can cause extremely nasty stuff," Bancroft said. "It can cause anything from something that's a self-limited decent size pimple all the way to death. It can cause a full range of outcomes."

Frequent hand-washing is the best known protection against Staph bacteria and both Bancroft and Simor suggested public education programs getting out that message would help to control spread.