Superbug 'genie is out of the bottle'

Staph aureus: Only a 'matter of time' before totally
resistant strain appears, experts fear
 
Helen Branswell
National Post

Monday, July 08, 2002
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TORONTO -- The U.S. Centers for Disease Control has announced the first confirmed case of staphylococcus aureus -- cause of some of the most common and troublesome infections to afflict man -- becoming resistant to the antibiotic arsenal's main weapon.

Vancomycin-resistant staph aureus -- known in the medical world as VRSA -- was found last month in a Michigan man.

Medical experts have long described this as the nightmare scenario of antibiotic resistance.

"The genie is out of the bottle," Dr. Donald Low, microbiologist-in-chief at Toronto's Mount Sinai Hospital, said of the confirmation. "It's ominous."

The news leaves experts such as Dr. Low contemplating a future in which common staph aureus infections will not be treatable with any antibiotics -- which was the case before the discovery of penicillin changed modern medicine. Prior to penicillin, many surgical procedures that now routinely save lives would have been too dangerous due to the risk of infection.

Penicillin is now nearly useless against staph aureus; overuse of the drug fuelled resistance, a process in which the rapidly evolving bug simply learns how to evade the drug's firepower.

Over the decades since antibiotics have become a staple of medicine, bacteria such as staph aureus and enterococcus have acquired resistance to a succession of antibiotics. Methicillin-resistant staph aureus (MRSA) and vancomycin-resistant enterococcus (VRE) are a fact of life in many hospitals.

People who acquire antibiotic-resistant strains of bugs generally pick them up in hospitals, where they thrive. But, increasingly, some of these bugs are moving out from behind hospital walls to infect people in the community.

Experts and organizations such as the Centers for Disease Control have been on the lookout for the development of a strain of staph aureus that is resistant to vancomycin. Given the growing rates of methicillin-resistant staph aureus and the vancomycin-resistant enterococcus, it seemed inevitable.

"It's only a matter of time before these two dance together in the right environment and this gene is shared. And this is exactly what's happened," Dr. Low said.

The gene he referred to is the one that conveyed vancomycin resistance to enterococcus. The interplay of the two bugs has allowed the gene to literally jump from enterococcus to staph aureus. It is actually called "a jumping gene."

The bad news could have been worse.

"It's not the totally resistant VRSA that we've been petrified of," said Shirley Paton, Health Canada's chief of nosocomial (hospital acquired) and occupational infections.

The Michigan man's staph infection responded to two new, less commonly used antibiotics, linezolid and quinupristin/dalfopristin. So his strain of staph aureus was not completely drug resistant. But those treatments are tremendously costly, costing between $150 and $200 a day compared to $10 a day for vancomycin.

And there have already been reports of resistance to linezolid in the United States, the first occurring within a year of the drug's introduction to the market.

The experts know the Michigan case is solid proof they will soon have to deal with their nightmare scenario -- completely resistant staph aureus.

"This is just a matter of time -- and one could liken it to a ticking time bomb," said Dr. John Conly, chairman of the Canadian Committee on Antibiotic Resistance and chairman of University of Calgary's medical school.

"It's a significant cause for concern ... And the concern is -- is this going to spread from patient to patient? Is this just the beginning or the tip of the iceberg? Are we now going to see this spreading as we saw in the 1950s when we are having epidemics of surgical wound infections due to vancomycin resistance? Are we going to run into the scenario where we've got no options for treatment of these patients?"

Some of those questions may be answered in October, when a major national policy conference on antibiotic resistance is scheduled to take place in Ottawa.

"I think it will really focus and crystallize attention on this issue," Dr. Conly said. "With the advent and arrival of VRSA, I think this appears to be a very timely meeting."

In the meantime, Health Canada will step up production of a set of guidelines on vancomycin-resistant staph aureus, Ms. Paton said.

"We have been working for about 18 months and will obviously speed this up in terms of ... writing a contingency plan related to vancomycin resistance in Canada," Ms. Paton said.

"That isn't published at this point ... but we'll be pulling out a few of the stops so that we'll move further ahead on it."

The plan will spell out guidelines on infection control in hospitals as it relates to VRSA -- how patients carrying the superbug are to be isolated, which public health authorities are to be notified, how laboratories need to gear up to recognize it.

"We want to be able to put walls around the organism as best we can to keep it from spreading to others," Ms. Paton said.