LAS VEGAS — Reno officials got a report on the “nightmare bacteria” in late August.
A Washoe County woman in her 70s had been admitted to a local hospital with a full-body response to an infection. It was carbapenem-resistant Enterobacteriaceae, or CRE, a bug resistant to all 26 federally approved antibiotics. The patient, whose identity has not been disclosed, died in early September, reported the Las Vegas Sun.
In Lei Chen’s years as an epidemiologist at the Washoe County Health District, she had investigated a case of Japanese encephalitis (a virus that causes brain inflammation), uncovered salmonella (the bacteria behind a brutal form of food poisoning) and studied the spread of coxsackievirus (otherwise known as hand, foot and mouth disease). But the lab results she received Aug. 25 were unfamiliar.
“I’ve never seen that kind of report,” Chen recalled recently, after publishing results of the incident through the Centers for Disease Control.
“Nightmare” is the dramatic epithet CDC director Tom Frieden used in a 2013 media release to describe CRE, a superbug that defies some of the strongest antibiotics. Experts noted that the incident in Washoe County was an extreme and rare case. Its significance is that it is one of the first instances of a U.S. patient dying of bacteria resistant to all FDA-approved antibiotics.
“It’s a wake-up call to us North Americans to realize that these bad bugs we’ve been hearing about are right here at home,” said James Johnson, an epidemiologist and professor at the University of Minnesota. “We need to take them seriously.”
Johnson was referring to the fact that some of the most resistant bacteria strains are clustered outside of North America, notably in India, where the Washoe County resident had reportedly spent two years.
“It’s very prevalent in India,” Chen said of CRE.
In the CDC publication, Chen and other investigators wrote that the patient had multiple hospitalizations in India during her time there. She was treated for a femur fracture, inflammation of the bone marrow and a hip procedure. Her last admission in India was in June, two months before returning to the U.S. Chen is fairly confident the patient contracted the bacteria in India. In fact, the protein responsible for her particular CRE’s resistance is called New Delhi Metallobetalactamase.
Upon the discovery that she had CRE, the patient was isolated and doctors took procedural precautions, including strict hand washing. Officials at the Washoe County hospital did not identify CRE in other patients admitted to the unit.
“We have known that bacteria resistant to all the antibiotics available are possible, but they’ve been a specter that has concerned people rather than something killing people on our doorstep,” Bill Hanage, a Harvard epidemiologist, wrote in an email. “This obviously changes that. However, it does not mean that they are common. Yet.”
Transmission of CRE can be difficult to track. With a team of researchers from the Harvard T.H. Chan School of Public Health and the Broad Institute, Hanage recently published findings that show wide variation in resistant bacteria. The research also suggests that CRE colonizes in healthy, asymptomatic patients, living peacefully in the gut. It turns dangerous when it enters the bloodstream or when a patient’s health is already insecure. The latter accounts for CRE’s presence in long-term care facilities.
That’s the kind of setting in the United States where CRE is likely to spread, as patients already are ill, take a lot of antibiotics and often make frequent trips to hospitals.
“The risk to the average person walking down the street is negligible,” said Alex Kallen, an epidemiologist and outbreak response coordinator at the CDC.
More focus should go into studying transmission pathways, Hanage said. “Any competent epidemiologist will tell you the best way to stop someone getting sick is to ensure they never get the bug in the first place,” he wrote. “And when it comes to resistance, we’ve been documenting increases without sufficient attention for how people pick up the bacteria ...”
But Hanage also noted that the Nevada case is rare. As of January, the CDC had received reports of at least 286 patients with CRE. In many instances, the bacteria are susceptible to at least some antibiotics. What made the Nevada case stand out was that the patient’s bacteria culture resisted all FDA-approved antimicrobial drugs.
“It is very uncommon for us to see isolates with this much resistance,” Kallen said.
The variation in resistance is controlled in part by the unique genetics of each bacteria culture, Hanage’s study found. In some cases, genes code for enzymes that thwart antibiotics. In other cases, mutated genes alter the cell’s physical structure, which can create a challenge for antibiotics attempting to infiltrate the bacteria.
Johnson, who also directs the molecular epidemiology unit at the Minneapolis VA Health Care Center, said bacteria develop resistance by picking up mutations in their genetic codes that favor their survival against antibiotics. The resistant bacteria often spread from there through human activities — travel, trade and food preparation.
In the U.S., there is little transmission taking place outside of health care settings, Kallen said. But he emphasized the importance of containment, highlighting the steps Washoe County took in isolating the victim and testing other patients. He said basic hygiene, such as hand washing, and precautions like wearing gloves, can help. Other experts suggest protecting patients by reducing antibiotic prescription.
“(The Nevada case is) a good example (of what) could await us if we don’t take it seriously,” Kallen said.
