Public Health: Ready for the Next Bug?
On June 20, Dr. Fred Tenover at the Centers for Disease Control & Prevention (CDC) got a sobering call. A female dialysis patient in southeastern Michigan had come down with a nasty infection that vancomycin, commonly called the antibiotic of last resort, couldn't kill. It was the first-ever confirmed report of a Staphylococcus aureus bug, a major menace, that was fully resistant to this powerful antibiotic. "This is the problem we had been fearing--and hoping would never come," says Dr. Marcus Zervos, an antibiotic-resistance expert at William Beaumont Hospital in Royal Oak, Mich. Suddenly, the world is a more dangerous place. And the emergence of the superbug is yet another worrisome reminder of how unexpected agents--whether bred in nature or in secret terror labs--could wreak havoc if not identified and checked quickly.
But the story also has a surprising twist. For years, public health pros have warned that America's ability to respond to new disease threats--including bioweapons--was crumbling. Then came last year's anthrax scare. Congress responded quickly, handing nearly $1 billion to the CDC for 2002 to help health departments and infectious-diseaselabs across the country better prepare for terrorist attacks. "We're also using the new investments to strengthen the public health foundation," says Director Dr. Julie L. Gerberding.
As a result, the nation's public health system is beginning a mini-resurgence. From Maryland to Mississippi, state health departments are tracking the spread of West Nile virus better than ever before. The upgrade is improving links between front-line EMS units and public health departments, helping to identify unusual disease outbreaks faster than in the past. Indeed, the sharpened capabilities needed to counter biological attacks are helping to fight everything from tuberculosis and food poisoning to the new drug-resistant staph infection. "At the end of the day, it's all about having adequate resources and personnel to do investigations of this sort," says Dr. Matthew L. Boulton, chief epidemiologist for the state of Michigan.
In the case of the vancomycin-resistant S. aureus, the public health system showed that the investment is paying off. Tenover got the long-dreaded call on Thursday afternoon. By Friday morning, a sample of the superbug arrived via FedEx at the CDC for analysis. By Sunday, the CDC had a team assembled and ready to travel to Michigan to help state and local investigators already on the scene. Within days, more than 400 people were tested to see if the staph infection had spread. The rapid response helped keep the microbe isolated to the one patient, where it was tamed with new antibiotics. "Two to three years ago, that call may have been returned on Monday morning," says Tenover. "But September 11 and [the anthrax attack] really showed us we have to communicate the same day, if not the same hour. This is an organism of great public health consequence--and we wereonit."
Almost as important as quashing the dangerous infection was figuring out how the patient's S. aureus germs acquired the ability to thwart vancomycin. And thanks to the recent boost to the public health system, Tenover and his colleagues were able to solve this mystery as well. They knew that vancomycin, a powerful antibiotic that was first discovered and used in the 1950s, works by attacking the fortress-like cell walls that bacteria build around themselves. The walls are made of sugar molecules bonded by amino acids, Tenover explains, and vancomycin attacks the amino acid links. Unable to build the protective walls, the microbes die.
For three decades, vancomycin worked like a charm, quashing dangerous hospital-acquired infections--such as enterococcus and staphylococcus germs--even when the bacteria were resistant to other antibiotics.
Then suddenly, in 1988, a strain of vancomycin-resistant enterococcus (vre) popped up. Somehow, the bacterium had been able to acquire five new genes, enabling it to replace the amino acid links with another molecule that the drug couldn't attack. "There must have been a whole series of trials and errors by the organism to get all the right genes and do it in the right order," says Tenover. In just a decade, vre's rapid spread has led to hundreds of millions of dollars in extra costs--and thousands of deaths-per year in hospitals.
Now, the Michigan case has provided U.S. health authorities with their first taste of a potentially worse threat,"the possibility of staph becoming resistant to vancomycin," says Zervos. Here's what happened. The Michigan patient harbored two bugs: one, a strain of S. aureus that was resistant to most other antibiotics; the other, a relatively rare species of VRE known to be promiscuous in spreading genes to other bacteria. As a result, the VRE genes were able to jump over to S. aureus.
This time, the infection never spread beyond that patient. But it will happen again, and the public health system has to be ready. "We might see another case next week--or not for years," says Tenover. By then, the potential consequences could be worse. Resistance is already emerging to the last-ditch antibiotics used in the Michigan case. "We need new antibiotics," says Dr. Stuart B. Levy, director of the Center for Adaptation Genetics & Drug Resistance at Tufts University School of Medicine. "We've got some time to breathe, but we are down to the last drug again."
The good news, however, is that health sleuths now stand a better chance of spotting and stamping out new drug-resistant germs or other types of infectious agents than they did before the anthrax attacks. While experts caution that the public health resurgence is only beginning, and that it still has a long way to go, our once shaky defenses against deadly microbial invaders have finally been given a badly needed boost.
By John Carey in Washington