A gene that strips away one of the last reliable classes of antibiotics is no longer a rarity imported from overseas. It is showing up in more American hospitals, and new wastewater data suggest it is also circulating in some communities outside of them.
Federal laboratory surveillance found that infections caused by carbapenem-resistant Enterobacterales carrying the New Delhi metallo-beta-lactamase gene, known as NDM, rose 461% between 2019 and 2023, according to a CDC report published in Annals of Internal Medicine and detailed by CIDRAP.
For most healthy people going about a normal week, this is not a personal threat. The risk concentrates sharply among hospitalized patients, especially those in intensive care with ventilators, catheters or long stays. But the reason infection specialists are paying attention is that NDM does not behave like a single germ, and that changes how it has to be tracked.
Why a Gene Spreads Differently Than a Bacterium
Most hospital outbreak investigations look for one organism moving between patients. NDM does not respect that model.
The gene is almost always carried on plasmids, small loops of DNA that bacteria can pass to one another. That means a bacterium can become resistant without ever having been exposed to an antibiotic, simply by picking up the genetic instructions from a neighbor.
Nathan Raabe, PhD, MPH, a genomic epidemiologist at the University of Pittsburgh School of Medicine, described the gene as inherently mobile, able to spread among any compatible host species capable of holding the plasmids that carry it. His colleague Alex Sundermann, DrPH, noted that other bacteria readily take it up because it improves their odds of survival.
The practical consequence showed up in a 2024 investigation at UPMC Presbyterian Hospital, where researchers documented an NDM outbreak involving 15 patients and seven different bacterial species. Some of the transmission was the plasmid moving, not a single strain spreading. Most hospitals cannot detect that pattern in real time because they are not sequencing at that level.
CDC research indicates the current increase is being driven mainly by a handful of strains from three members of the CRE family: Klebsiella pneumoniae, Escherichia coli and the Enterobacter cloacae complex.
Why Treatment Options Are So Limited
All CRE infections are difficult. The CDC labeled them an urgent threat in its 2019 antibiotic resistance report, and mortality across CRE infections ranges from roughly 30% to 50%.
NDM-carrying infections add a specific problem. Several newer combination antibiotics were designed to defeat other carbapenemase genes and do not work against NDM. For years that left clinicians in a position where the newest drugs on the shelf simply did not apply.
That has partly changed. Aztreonam-avibactam, approved by the Food and Drug Administration in early 2025, gives clinicians another option. But the drug only helps if the infection is correctly identified as NDM-carrying, and many clinical laboratories lack the molecular testing needed to detect it.
Danielle Rankin, PhD, MPH, a CDC epidemiologist, said when the agency released its findings that "selecting the right treatment has never been more complicated," and stressed the need for provider access to testing that guides targeted therapy.
Richard Stanton, PhD, a bioinformatician with the CDC's Division of Healthcare Quality Promotion, told CIDRAP that "the rapid increase is a major concern for CDC," citing both treatment implications and the possibility of spread outside healthcare settings.
What Wastewater Data Add and What They Do Not
That second concern is where the newer research comes in. A team led by researchers at the University of California, Berkeley analyzed wastewater from 163 U.S. sites and published the results in Nature Communications in April.
NDM was undetectable in some parts of the country. Concentrations were higher in communities served by hospitals and nursing homes, particularly in southern and western states. The study also found that NDM presence was significantly associated with socioeconomic factors including lack of health insurance, overcrowding and housing burden.
Those associations are correlations. The senior author, Amy Pickering, PhD, an associate professor at UC Berkeley, said the mechanisms behind them are unclear and need further investigation. The study cannot establish that any of those factors cause higher NDM levels.
The variability itself was the notable finding. Several other resistance genes the team measured turned up at high concentrations everywhere, which makes them useless for distinguishing one community from another. NDM varied enough to potentially signal real regional differences.
WastewaterSCAN has since added NDM to its national dashboard. Its scientific program manager, Amanda Bidwell, MS, cautioned that interpretation will take time, because unlike seasonal flu there is no clear annual signal. It is not yet possible to tell whether a site showing high concentrations is experiencing a spike or simply has a high baseline because a large hospital sits within the sewershed.
The geographic picture, in short, remains incomplete. That is the most important limitation of the current evidence.
Who Is Actually at Risk and What Readers Can Do
The people who face meaningful risk are hospitalized patients, particularly in intensive care, those with invasive devices, transplant recipients, and people with prolonged or repeated hospital stays. Residents of long-term care facilities and patients transferred between institutions also carry higher exposure. International medical care, especially in regions where NDM is more common, is another established risk factor.
There is no consumer product to avoid and no screening test a healthy person should seek. What families can reasonably do is ask questions when a relative is admitted with a serious infection: whether cultures have been taken, whether resistance testing is being done, and what the isolation precautions are.
The broader lever is antibiotic use. Brad Spellberg, MD, chief medical officer at the Los Angeles General Medical Center, argued that resistance will eventually emerge to whatever is developed next, and that the more durable answer is controlling antibiotic use so these organisms are not repeatedly selected for in healthcare settings.
That points to an ordinary household action with real weight: not pressing a clinician for antibiotics for viral illnesses, and finishing courses as prescribed rather than saving leftovers.
What Happens Next
The picture is genuinely mixed. Separate CDC survey data show healthcare-associated infections overall have declined in recent years, which means the NDM increase is running against a broader improvement rather than alongside a general collapse in infection control.
Researchers expect several months of additional wastewater data before regional NDM patterns can be interpreted with confidence. Hospitals with genomic capacity will continue tracking plasmid movement, and CDC surveillance updates will show whether the 461% increase has continued past 2023.
The confirmed fact today is that NDM-carrying CRE infections rose sharply through 2023 and that the gene has been detected in community wastewater in some regions. The most affected group is hospitalized patients with invasive devices. The reasonable action for households is careful antibiotic use and informed questions during a hospital stay. The central uncertainty is where the gene is concentrated geographically and why.
Frequently Asked Questions
What is NDM? NDM stands for New Delhi metallo-beta-lactamase. It is a gene that makes bacteria resistant to carbapenems, a class of last-resort antibiotics, and often to other antibiotics as well.
How much have these infections increased? CDC surveillance found that CRE infections carrying NDM genes rose 461% from 2019 through 2023.
Why is a gene harder to track than a germ? NDM is carried on plasmids that move between bacterial species. An outbreak can involve several different bacteria sharing the same resistance gene, which standard hospital surveillance is not designed to detect.
Who is most at risk? Hospitalized patients, especially those in intensive care with ventilators or catheters, people with long or repeated hospital stays, long-term care residents and patients who received medical care in regions where NDM is common.
Is there any treatment? Aztreonam-avibactam, approved in early 2025, is an option for NDM-carrying infections. It only helps if the infection is identified as NDM-carrying, and many labs lack that testing capability.
Does the wastewater finding mean my community is unsafe? No. The gene was undetectable at some sites, and higher readings may reflect a nearby hospital rather than community spread. Researchers say months more data are needed before the patterns can be interpreted.
What can an ordinary household do? Avoid pressing for antibiotics for viral illnesses, take prescribed courses as directed, and ask about cultures, resistance testing and isolation precautions if a relative is hospitalized with a serious infection.
