Deadly bacteria’s foothold spurs study
Mass. specialists try to halt spread
News that a hard-to-treat, potentially lethal germ had landed on US shores from India spawned sensational headlines last month about the emergence of a “superbug’’ capable of outwitting the best antibiotics available. So far, just three cases of this NDM-1 bacterium have been identified in the United States — including one in Boston.
But its genetic cousin has been spreading for several years in US hospitals, stoking sufficient concern that the Massachusetts Department of Public Health intends in coming weeks to survey hospitals to gauge the incidence of the bacteria.
Interviews with specialists at Boston teaching hospitals suggest that the germ has established a foothold in New England and even led to some deaths, but that cases tend to be sporadic and share no obvious common source.
Known as Klebsiella pneumoniae, the drug-resistant bacterium has been detected in 35 states. Like the superbug identified in New Delhi, it can devour a class of antibiotics that infectious disease specialists keep in reserve for the toughest cases, leaving physicians with few options when patients develop urinary tract, bloodstream, or respiratory infections.
“They’re both really bad, and you don’t want to get [them],’’ said Dr. Helen Boucher, an infectious disease specialist at Tufts Medical Center.
So why has the more recent vintage bug garnered such attention? “Maybe it’s the international flavor that’s kind of more sexy: ‘Oh, it came on an airplane.’ That gets people’s attention,’’ she said.
The presence of the home-grown germ, first found in the United States a decade ago and confined thus far to hospital patients left vulnerable by other illnesses or surgeries, underscores worries about the rapid appearance of drug-resistant bacteria, the slow pace of antibiotic development, and the potential for the bacteria to escape hospital walls. It has also intensified surveillance efforts on hospital wards and redoubled campaigns to prevent the germ’s spread.
“Yes, it’s true we don’t have enough antibiotics anymore,’’ said Dr. Alfred DeMaria, epidemiologist at the Massachusetts Department of Public Health. “But the real problem is we have too many infections. We need to slow down these organisms.’’
It was in North Carolina that scientists first identified Klebsiella bacteria that harbored the ability to evade antibiotics called carbapenems, a category of drugs summoned when everything else fails. Back then, fewer than 1 percent of all Klebsiella infections in the United States carried the trait.
Today, 8 percent have the escape mechanism, an enzyme that goes by the acronym KPC.
“This is important because the carbapenem antibiotics have for many years been a very reliable go-to agent when we were worried about highly drug-resistant infections,’’ said Dr. Arjun Srinivasan, who specializes in infection prevention at the US Centers for Disease Control and Prevention.
Infectious disease specialists believe overuse of these drugs is to blame.
Even when medicines are prescribed correctly against bacterial infections, an inevitable Darwinian tug-of-war plays out: The drugs are most successful at vanquishing the tamest bugs, allowing hardier ones such as the KPC strains to proliferate.
One study found that having received a carbapenem drug increased the risk of acquiring a drug-resistant Klebsiella strain by 15 times compared with patients not exposed to the medication.
But unlike another drugresistant germ that has gained widespread prominence and goes by the acronym MRSA, Klebsiella doesn’t typically sit on the skin or inside the nose. It generally remains in the intestinal tract, causing no problems — unless it finds a way to escape. That can happen when a patient has undergone surgery or some other medical treatment that causes incisions or requires invasive medical equipment to provide or remove fluids, or sustain breathing.
“It’s true that most of these patients have seen a lot of antibiotics, including carbapenems, and have had their primary defenses against infection violated, either through catheters or procedures or medical devices and are at high risk of getting infections,’’ said Dr. Deborah Yokoe, an epidemiologist at Brigham and Women’s Hospital.
The Brigham, like several other Boston teaching hospitals, has treated episodic cases of drug-resistant Klebsiella in the past year. Last October and November, specialists at Massachusetts General Hospital detected a cluster of about 10 patients infected with the bacteria.
The Mass. General doctors went into full medical detective mode to determine whether the patients, some referred from other hospitals not equipped to handle such complex cases, shared a common source, either outside Mass. General or inside. Although the germs are not highly transmissible — they are not, for example, spread through a cough or a sneeze — they can travel if a health care worker does not follow good hand-washing and other hygiene practices.
“We looked for common features,’’ said Dr. David Hooper, chief of Mass. General’s infection control unit. “We didn’t find any.’’
Three of the patients died; all of them had significant underlying health problems.
Doctors who encounter patients with a drug-resistant Klebsiella infection confront a nearly barren medicine cabinet. One of the two drugs they use, colistin, had largely been abandoned years ago because it is so toxic to the kidneys.
“Often, if the person is really sick and they’re not doing well, we end up having to do the colistin routine,’’ Boucher said, “and we hold our breath.’’
Stephen Smith can be reached at firstname.lastname@example.org.