U.S. military men and women gravely wounded in Iraq and Afghanistan face another threat
A. baumannii infection affects hospitalized patients at their most vulnerable. Now, antibiotics that once could overcome the dangerous bacteria have lost nearly all effect.
Left alive when a 500-pound car bomb in Baghdad killed two others on her TV crew, CBS News reporter Kimberly Dozier required an arduous chain of surgeries for the life-threatening wounds she sustained that May day in 2006. In the midst of her months-long medical battle—after military doctors "had pared away the dead, burned muscle tissue in my upper right leg," as Dozier later wrote—the journalist’s recovery was jeopardized by the menacing bacteria Acinetobacter baumannii.
The bacteria typically prey on patients who, like Dozier, are confined to the hospital and are extremely ill and vulnerable. Just one among more than 20 Acinetobacter (ass in ée toe back ter) species, Acinetobacter baumannii, or A. baumannii, is responsible for the vast majority of infections from this bacterial family. Infection can lead to diseases ranging from pneumonia to serious blood infections.
Though the medical community has long been aware of the bug, A. baumannii has received widespread attention recently for its conspicuous impact on wounded American soldiers returning from Iraq and Afghanistan. According to a report in the February 2008 issue of the military publication Proceedings, at least 250 Acinetobacter infections occurred at U.S. military health facilities in a two-year period beginning in March 2003.
Outbreaks are not limited to military settings, however. "A few outbreaks at military hospitals have gotten a great deal of attention, but it’s not a soldier’s disease," emphasizes Mark Adams, Ph.D., who studies A. baumannii in the Department of Genetics at Case Western Reserve University’s School of Medicine. Total incidence of infection from the pathogen is hard for health experts to pin down, but the Infectious Diseases Society of America estimates that Acinetobacter is responsible for about 3 percent of all health care-associated infections (infections from exposure during surgery or other treatment in medical facilities).
Experts agree A. baumannii is far from the most prevalent bacteria around. Nor is it the most virulent. Other bacteria, Staphylococcus aureus among them, are substantially more toxic. A. baumannii has recently raised concern in the medical community for another reason: its ever-growing ability to outsmart commonly prescribed antibiotics. Now, more than one-third of A. baumannii infections are resistant to multiple drugs, Adams says.
Robert Bonomo, M.D., a physician with Case Western Reserve University’s School of Medicine and the Louis Stokes Cleveland VA Medical Center, agrees. "This organism is of real clinical concern to us right now. As a cause of infection in the intensive care unit, A. baumannii is among the worst of the worst because it has become so difficult to treat."
A. baumannii can live on the skin and be transferred from one person to another, or spread through contact with contaminated surfaces or exposure in the environment. Infection-control steps, such as hand washing and environmental cleaning, can diminish the likelihood of transferring the bacteria, according to the Centers for Disease Control and Prevention.
For most people exposed to Acinetobacter, the pathogen lives or "colonizes" on the skin without causing any health problems. Infection begins only when the bacteria find an opportunity to enter the bloodstream.
"Normal, healthy people don’t get infected," says Bonomo. "Even people admitted to the hospital are at no risk except under the most unusual progression of circumstances. You’re talking about critically ill patients with suppressed immune systems, many of them on ventilators and requiring extensive surgical treatment."
Like reporter Dozier, Marine Cpl. David "DJ" Emery—who has since been promoted to sergeant—battled infection from A. baumannii while in the hospital with grievous injuries from a bomb blast in Iraq. But while Dozier lost neither life nor limb in her fight against Acinetobacter, Emery had a very different outcome. In the hospital after losing a leg in a February 2007 suicide bombing near the city of Haditha, his recuperation took a calamitous turn: A. baumannii—better known to U.S. forces simply as "Iraqibacter"—was discovered infecting Emery’s body and forced the amputation of his other leg by military surgeons.
It’s relatively uncommon, experts say, for someone to become infected with A. baumannii at the time of an initial injury. Where A. baumannii infections originate can be difficult to pinpoint. "There’s no simple answer," Adams says, adding that an early notion that Iraqi soil was a primary source of the bacteria has been discredited. Drug-resistant strains of A.baumannii may have gotten a foothold in Iraq, however, because of different hygiene standards or inappropriate use of antibiotics in the country, experts say.
In the United States, A. baumannii has made a name for itself as a "bad bug"—one of six bacteria that are increasingly immune to current antibiotics and for which the Infectious Diseases Society of America has put out an urgent call for new drugs. The bacteria’s most disturbing feature is its "remarkable level of resistance" to available antibiotics, physician-researcher Bonomo says.
Glenn Wortmann, M.D., chief of infectious disease at Walter Reed Army Medical Center, says physicians are having to alter the way they treat infected patients. "We’re having to go for broaderspectrum antibiotics, where in the past we could pick a fairly common one."
Physicians who once treated A. baumannii with standard drugs today find themselves resorting to toxic alternatives—sometimes gambling on the drug colistin, developed in the 1950s and known to be perilous to a patient’s kidneys.
No promising drugs are even in the pipeline for A. baumannii. Some researchers, however, are beginning to decipher the pathogen’s resistance mechanisms, which could support development of new treatments.
In one landmark study, published in the December 2008 Journal of Bacteriology, researchers scrutinized A. baumannii’s complex genetic makeup. The team, led by Case Western Reserve genetics expert Adams, observed quick DNA changes in A. baumannii bacteria. Even within a single outbreak in a hospital, each patient’s infection carried substantially different resistance genes that could affect response to antibiotics.
"Because of the disparate genetic characteristics, we found it’s not as simple as ‘You have this bug so you should get this antibiotic,’ " Adams says.
"This snapshot represents an important step toward explaining the organisms’ unique adaptability to life in a hospital, and also to life in patients themselves," explains Bonomo, who collaborated on the study. The research is ongoing, with the team aspiring to develop screening tests to reveal resistance mechanisms and targeted antibiotics to bypass resistance.
When journalist Dozier’s body managed to fend off the uniquely adaptable Acinetobacter bug without the need for noxious medicines, it was, she wrote, thanks to a "measure of luck." Doctors hope to rely soon on new, effective antibiotics—not on chance—to gain the upper hand against the bacteria.
"Unless we can find a way to undermine the success of this pathogen," writes Bonomo and co-authors of a June 2008 editorial in Expert Review of Anti-infective Therapy, "it is safe to conclude that A. baumannii will be with us for the long haul."
In the short term, emphasis is placed on cautious use of antibiotics—given the well-known association between their misuse and bacteria’s increased resistance. Also being stressed is the importance of optimizing infection-control procedures in health-care settings to prevent the pathogen’s spread.
And for now, Walter Reed physician Wortmann is pleased to have observed a recent drop in Acinetobacter incidence. He credits not only better infection control procedures, but also another factor: "Fortunately," he says, "we’re also helped by a decreased number of casualties coming through the door, which translates into fewer cases of Acinetobacter."