CRE stands for carbapenem-resistant Enterobacterales, a group of bacteria that have developed resistance to carbapenems, which are among the most powerful antibiotics available. The CDC estimates roughly 13,100 CRE infections occurred in hospitalized patients in the U.S. in 2017, leading to about 1,100 deaths. These bacteria are considered one of the most urgent antibiotic resistance threats in the world.
The Bacteria Behind CRE
Enterobacterales are a large order of bacteria that naturally live in the human gut. Most of the time they’re harmless, but they can cause serious infections if they spread to the bloodstream, lungs, or urinary tract. The two species most commonly associated with CRE are Escherichia coli (E. coli) and Klebsiella pneumoniae. When these otherwise treatable bacteria develop carbapenem resistance, infections become far more dangerous because the go-to backup antibiotics no longer work.
How CRE Resists Antibiotics
The main way CRE bacteria survive carbapenem treatment is by producing special enzymes called carbapenemases. These enzymes physically break apart the antibiotic molecule before it can kill the bacteria. Several types of these enzymes exist, and the type matters because it determines which treatments might still be effective.
What makes CRE especially concerning is that the genetic instructions for producing these enzymes can sit on small, mobile pieces of DNA. Bacteria can pass these DNA fragments to neighboring bacteria, even bacteria of different species. This means resistance can spread rapidly through a hospital environment, turning previously treatable infections into difficult ones almost overnight.
Who Is Most at Risk
CRE infections overwhelmingly affect people who are already in healthcare settings. Patients in intensive care units, those on mechanical ventilators, and people with long-term urinary catheters or IV lines face the highest risk. The bacteria can enter the body through these medical devices or through wounds, and a weakened immune system makes it harder to fight the infection once it takes hold.
Long-term care facilities and nursing homes are another common setting. Patients who have taken multiple rounds of antibiotics are also at elevated risk because those drugs can wipe out the protective bacteria in the gut, leaving room for resistant strains to take over.
Colonization Versus Active Infection
Not everyone who carries CRE gets sick from it. Some people become “colonized,” meaning the bacteria live on their skin or in their gut without causing symptoms. Colonized individuals feel perfectly fine but can still spread the bacteria to other patients, which is why hospitals screen for CRE even in people who show no signs of illness. An active infection, by contrast, produces symptoms like fever, pain, or organ dysfunction depending on where the bacteria have settled, whether that’s the bloodstream, urinary tract, or lungs.
Why CRE Is Classified as Critical
The World Health Organization ranks carbapenem-resistant Enterobacterales in its highest threat category: critical priority. This designation, reaffirmed in the 2024 update to the WHO’s priority pathogens list, signals that these bacteria pose the greatest risk to human health and that new treatments are urgently needed. The critical label places CRE alongside only a handful of other resistant pathogens at the very top of global concern.
The high mortality rate drives this classification. CRE bloodstream infections can kill up to half of infected patients in some clinical settings, largely because so few effective drugs remain once carbapenems fail.
How CRE Infections Are Treated
Treatment depends heavily on which resistance enzymes the specific bacteria produce. Over the past decade, several newer antibiotics have been developed that pair a traditional drug with a compound designed to block the resistance enzyme, essentially restoring the antibiotic’s ability to work.
For bacteria that produce the most common resistance enzyme (KPC), doctors have multiple newer options that combine an antibiotic with an enzyme blocker. These combinations have significantly improved outcomes compared to the older, more toxic drugs that were once the only choice. For bacteria producing a different enzyme type called an MBL (common in parts of Asia), treatment is harder. One approach combines two different antibiotics that together can overcome the resistance, though options remain limited.
A newer antibiotic uses an unusual strategy: it hitches a ride into the bacterial cell by mimicking iron, a nutrient bacteria actively absorb. This approach works against nearly all types of CRE, regardless of which resistance enzyme they carry, making it a valuable option when the specific enzyme type is unknown or when other drugs fail.
Additional combination drugs are currently in late-stage clinical trials, which may expand options further for the hardest-to-treat enzyme types.
How Hospitals Prevent Spread
Stopping CRE from moving between patients is considered just as important as treating individual infections. In hospitals, patients with CRE are placed in isolation with contact precautions, meaning healthcare workers wear gloves and gowns before entering the room. In nursing homes, the approach may involve enhanced barrier precautions or full isolation depending on the situation.
Beyond isolation, hospitals enforce strict hand hygiene protocols, thorough cleaning of surfaces and equipment, and careful management of catheters and other devices. Identifying colonized patients early through screening tests is a key part of the strategy, since people carrying CRE without symptoms can silently spread it to more vulnerable patients nearby. These combined measures have proven effective at containing outbreaks when followed consistently.