May 14, 2010 / 9:18 PM / 7 years ago

Faster, stronger, deadlier: the MRSA superbug

NEW YORK (Reuters Health) - When she first described it in 1961, Patricia Jevons, a British bacteriologist, may have had a hard time imagining that the tiny bug she was staring at would soon become a penicillin-mocking juggernaut -- a superbug that kills an estimated 19,000 Americans a year and make millions more sick.

Methicillin-resistant Staphylococcus aureus -- or MRSA for short -- is the subject of journalist Maryn McKenna's new book Superbug: The Fatal Menace of MRSA (Free Press, March 2010). She spoke with Reuters Health on Thursday about the bacteria's toll on public health and how we may, unwittingly, be helping a new strain along (see more here with-maryn-mckenna-author-of-superbug-the-fatal-menace-of-mrsa/).

"One of the problems with MRSA, one of the reasons why it's become what I consider a true crisis, is that I really don't think we've been taking it sufficiently seriously for a very long time," McKenna said.

MRSA first crossed the Atlantic in 1968, landing in what used to be called Boston City Hospital. Then it inched its way across the country until 1980, when it infected a burn victim at Harborview Medical Center in Seattle and caused a devastating outbreak.

"For more than a year, it hop-scotched from patient to patient," McKenna explained. "Eventually they closed both the (intensive-care unit) and the burn unit and built new ones, and still had new cases."

"That was the outbreak that really demonstrated how serious hospital infections with MRSA could be. Nevertheless, that was 30 years ago. American healthcare is still locked in a death struggle over what really are the best strategies for controlling MRSA and other drug-resistant organisms in hospitals."

In Europe, McKenna added, many hospitals test patients for the bug when they first arrive. If they test positive, they are kept in isolation until they have been treated successfully. But the strategy has never gained a strong foothold in the US.

But hospitals aren't the only breeding ground for MRSA: A strain known as community-MRSA has been around for years. Although there isn't sufficient surveillance, according to McKenna, one study estimated that seven million Americans make a trip to the doctor every year because of these bacteria.

Lowering your risk of contracting a MRSA infection isn't difficult, though. A simple thing like good hand hygiene, for instance, can go a long way, because the bacteria need to get into the body to do harm, and hands are the perfect vehicle.

CUBIST ENTERS THE ANTIBIOTIC ARMS RACE

Once inside the body, however, MRSA is very hard to kill. For years, the drug doctors called on when all others failed was vancomycin, an old, rarely used medicine with significant side effects.

As other drugs started to lose potency, vancomycin became the go-to drug. But MRSA responded by developing resistance to vancomycin, too, and pharmaceutical companies had to look around for new drugs in the ongoing arms race against the bacteria. Many of them had already lost interest in antibiotics, because resistance was likely to make the drugs ineffective -- and unprofitable -- in little time.

Cubist Pharmaceuticals was one of the companies that took on the challenge of battling MRSA. In the late 1990s, it decided to focus on a molecule -- daptomycin -- that had been isolated earlier by another company. What this meant, however, was that Cubist had to come up with a new dosing of daptomycin in order to get a patent.

In addition, to get approved by the US Food and Drug Administration, daptomycin had to match the best drug on the market. In the case of pneumonia, this drug was ceftriaxone, marketed as Rocephin. Daptomycin lost to Rocephin in a trial, although the margin wasn't huge. The problem was that Rocephin didn't work on MRSA, which is a different bacterium from the one usually causing pneumonia.

"Daptomycin, envisioned as a new weapon against MRSA, had been judged less successful than a drug that MRSA had been resistant to for years," McKenna writes in her book.

Although daptomycin was eventually approved by the FDA in 2003, McKenna said Cubist's struggle illustrates the challenges of finding new antibiotics.

An added measure of irony, she said: Daptomycin's main developer, Dr. Frank Tally, died from a Staph infection of the heart just as the drug was being approved for treating MRSA in the bloodstream, the most severe infections.

A TESTING GROUND FOR NEW RESISTANCE

There's another problem, possibly even bigger than antibiotics' lack of profitability, said McKenna: Our agricultural practices encourage the development of new drug resistance.

In 2004, a 6-month-old Dutch girl was brought to the hospital for a heart defect. But a routine check for MRSA revealed something potentially much worse: An unfamiliar strain of the bacteria that had also developed resistance to antibiotics not used to treat Staph infections in humans.

It turned out the girl's family were pig farmers. Presumably, the widespread use of antibiotics in their animals had turned the pigs into the perfect testing ground for bacteria developing new ways to evade our drugs.

"Since that finding in 2004, this strain has now hop-scotched around the globe and it's caused serious illnesses, including hospital and nursing home outbreaks in the Netherlands and in other places in the European Union," McKenna said.

And, she added, "just a couple of weeks ago, it was discovered to be causing serious surgical infections in people in three provinces in Canada, who had never been anywhere near agriculture."

In the US, only researchers from the University of Iowa have looked for the new strain -- and they found it in about half the pigs and pig farmers they tested.

In an ongoing study, the researchers are homing in on the bug's origin by comparing organic farms to conventional ones. None of the pigs in organic farms harbored MRSA, it turned out, while about a quarter of those in conventional farms did. The latter tend to be generous with antibiotics: Instead of treating just one sick animal, they give the whole herd medicine because it's more cost-effective, McKenna said.

"When we give antibiotics to healthy beings, in human medicine we call it inappropriate use of antibiotics," she said. The Centers for Disease Control and Prevention "has very aggressive campaigns to try to get physician to stop doing that. But we've kind of let it slide on agriculture for a very long time."

"You can buy antibiotics without a prescription if you go to a farm supply store. There are people in the Midwest who do buy antibiotics that way rather than go to Canada for cheaper drugs."

McKenna said the new MRSA strain had already been found in retail meat in the US and Canada, although she estimates there have only been a couple dozen human infections so far.

"Maybe that's not very many," she said. "But in 1998, there were only 25 cases of community-MRSA in Chicago, and now we have more than seven million a year. So, are we at the bottom of a tall epidemic curve, or is it always just going to sort of dribble along and not be important? At this point, no one can say."

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