An ESBL infection is caused by bacteria that produce enzymes called extended-spectrum beta-lactamases, which break down many common antibiotics before they can work. These aren’t exotic or rare bacteria. They’re ordinary gut bacteria, most often E. coli and Klebsiella pneumoniae, that have acquired the ability to resist a wide range of antibiotic treatments. The “infection” itself looks like any other bacterial infection (urinary tract infections, bloodstream infections, wound infections), but it’s significantly harder to treat because the usual antibiotics fail.
How ESBL Bacteria Resist Antibiotics
Most antibiotics used for common bacterial infections belong to a family called beta-lactams. This includes penicillins, cephalosporins, and a drug called aztreonam. They all share a chemical structure, a ring shape called the beta-lactam ring, that lets them latch onto bacteria and kill them.
ESBL-producing bacteria make enzymes that physically break open that ring. The enzyme grabs the antibiotic molecule, snaps the ring apart with a water molecule, and releases the now-useless drug fragments. The bacterium is free to keep multiplying. This process happens rapidly and repeatedly, so even high doses of these antibiotics can’t overcome the resistance. The bacteria chew through third- and fourth-generation cephalosporins, which are powerful antibiotics typically reserved for serious infections, and aztreonam. That leaves doctors with a much narrower set of treatment options.
Where These Infections Happen
ESBL infections have traditionally been associated with hospitals and nursing homes, where antibiotic use is high and resistant bacteria circulate among vulnerable patients. But the landscape is shifting. A systematic review of U.S. data found that the majority of ESBL E. coli infections (82.7%) and ESBL Klebsiella infections (71.1%) at community hospitals were actually community-onset, meaning patients arrived already carrying the resistant bacteria. About half of those patients were nursing home residents.
More concerning, studies have found that community-onset ESBL infections are increasing at a statistically significant rate, while hospital-onset rates have remained more stable. Roughly 2% of healthy people in the Americas carry ESBL-producing bacteria in their gut without any symptoms, a figure that rises to 14% globally. International travel is one way people pick up these bacteria. You can carry them for weeks or months without knowing, only discovering the resistance when an infection develops and standard antibiotics don’t work.
The COVID-19 pandemic made things worse. CDC data from a 2024 update showed that hospital-onset infections from several resistant bacteria, including ESBL producers, increased by a combined 20% during the pandemic compared to pre-pandemic levels, peaking in 2021 and remaining elevated through 2022.
What ESBL Infections Look and Feel Like
ESBL bacteria cause the same types of infections as their non-resistant counterparts. The most common is a urinary tract infection: burning during urination, frequent urges to go, cloudy or foul-smelling urine, and sometimes lower abdominal pain. You wouldn’t be able to tell it apart from an ordinary UTI based on symptoms alone. The difference only becomes apparent when the first round of antibiotics doesn’t clear it up, or when lab results come back showing resistance.
These bacteria can also cause wound infections, pneumonia (especially in ventilated hospital patients), and abdominal infections. In serious cases, bacteria enter the bloodstream, causing bacteremia or sepsis. The symptoms of ESBL-related sepsis are the same as any sepsis: high fever, rapid heart rate, confusion, and a sharp drop in blood pressure. What makes it more dangerous is the delay in getting an antibiotic that actually works.
Why Delayed Treatment Is Dangerous
When doctors treat a serious infection with an antibiotic the bacteria are resistant to, every hour counts. Research on ESBL bloodstream infections found that more than 25% of patients with sepsis and organ failure experienced a delay of more than one day before receiving an effective antibiotic. That delay contributed to a mortality rate of 51.9% among patients with severe sepsis and septic shock.
Organ failure during ESBL sepsis carries a 4.5-fold higher risk of death. Pre-existing kidney disease increases the risk 2.7-fold, and liver disease raises it 1.8-fold. These numbers underscore why rapid identification of ESBL resistance matters so much. The infection itself isn’t inherently more aggressive than a normal bacterial infection. The danger comes from lost time spent on antibiotics that can’t do their job.
Who Is Most at Risk
Recent antibiotic use is the strongest predictor. Taking a third-generation cephalosporin within three months of a new infection raises the odds of an ESBL infection nearly 16-fold. Prior use of fluoroquinolones (a common class of antibiotics prescribed for UTIs and respiratory infections) increases risk about 8-fold. Any antibiotic exposure lasting more than 24 hours in the preceding three months is considered a risk factor.
Other factors that raise your risk include recent hospitalization, living in a nursing home or long-term care facility, having a urinary catheter, and recent international travel, particularly to regions in South Asia, Southeast Asia, and parts of Africa where ESBL bacteria are more prevalent. Older adults and people with chronic illnesses face higher risk because they tend to have more contact with healthcare settings and more frequent antibiotic courses.
How ESBL Is Detected
If your doctor suspects antibiotic resistance, a sample (urine, blood, wound swab) goes to the lab for culture and sensitivity testing. The lab grows the bacteria and tests which antibiotics kill them. ESBL production is confirmed through specific methods that pair a cephalosporin antibiotic with a substance called clavulanic acid, which blocks the ESBL enzyme. If the antibiotic works dramatically better when clavulanic acid is present (at least an eightfold improvement), the bacteria are confirmed as ESBL producers.
Many hospitals now use automated systems that can run both screening and confirmatory tests on the same plate, speeding up detection. For more precise identification of which resistance genes are involved, labs use molecular testing, most commonly PCR, which can identify specific gene families in a matter of hours rather than the day or more that traditional culture methods require. Faster identification means faster switches to effective treatment.
Treatment Options
ESBL infections are treatable, but the antibiotic options are limited. Because ESBL enzymes destroy most penicillins, cephalosporins, and aztreonam, doctors typically turn to a different class of antibiotics called carbapenems, which are resistant to ESBL enzymes. For uncomplicated urinary tract infections, certain older antibiotics that aren’t affected by ESBLs may still work, depending on the specific bacteria’s sensitivity profile.
Treatment decisions depend entirely on the lab results showing which antibiotics your particular bacteria respond to. This is why the culture and sensitivity test is so important. There’s no one-size-fits-all answer, and an antibiotic that works for one ESBL infection may not work for another. For mild infections like uncomplicated UTIs, treatment is often oral antibiotics taken at home. For bloodstream infections or sepsis, treatment involves intravenous antibiotics in a hospital, sometimes for two weeks or longer depending on the source and severity of infection.
Reducing Your Risk
The most effective thing you can do is avoid unnecessary antibiotic use. Every course of antibiotics you take, whether it helps or not, shifts the bacterial population in your gut toward more resistant strains. If your doctor prescribes antibiotics, take the full course as directed. Don’t request antibiotics for viral infections like colds or flu, where they do nothing but increase resistance pressure.
Good hand hygiene is the single most effective way to prevent transmission, both in hospitals and at home. If you’re caring for someone with a known ESBL infection, wash your hands thoroughly with soap and water after any contact. In healthcare settings, patients with ESBL infections are typically placed under contact precautions, meaning healthcare workers wear gloves and gowns and use dedicated equipment to prevent spreading the bacteria to other patients. If you’ve recently traveled internationally and develop an infection, let your doctor know so they can factor potential resistance into their treatment choices from the start.