ESBL Bloodstream Infections: Why Choose Meropenem?

Why does the CDC warning matter for bloodstream infections?

The CDC's COVID-19 and antimicrobial resistance overview describes a setback in infection control: resistant hospital-onset infections and associated deaths each increased by at least 15% across seven pathogens between 2019 and 2020. Staffing shortages, disrupted prevention practices and longer hospital stays complicated care. These historical findings describe the pandemic's impact; they do not establish infection rates for October 2026. [CDC pandemic resistance overview](https://www.cdc.gov/antimicrobial-resistance/data-research/threats/COVID-19.html).

One relevant group is extended-spectrum beta-lactamase-producing Enterobacterales, or ESBL-E. These bacteria, which include some strains of E. coli and Klebsiella pneumoniae, manufacture enzymes that disable certain antibiotics. They can cause urinary tract and bloodstream infections, although some people carry them without symptoms. Serious infections may require hospitalization and intravenous treatment. The treatment challenge is choosing an antibiotic that remains effective despite the organism's resistance mechanisms. [CDC explanation of ESBL-producing bacteria](https://www.cdc.gov/esbl-producing-enterobacterales/about/).

What did the MERINO trial reveal about meropenem?

Published in JAMA in 2018, MERINO randomized 391 adults with bloodstream infections caused by ceftriaxone-resistant E. coli or Klebsiella pneumoniae that initially tested susceptible to piperacillin-tazobactam. Most isolates subsequently tested had ESBL genes. In the primary mortality analysis, 23 of 187 patients receiving piperacillin-tazobactam died within 30 days, compared with seven of 191 receiving meropenem: 12.3% versus 3.7%. The trial failed its noninferiority objective, meaning it could not demonstrate that piperacillin-tazobactam preserved an acceptable level of effectiveness compared with meropenem. [MERINO randomized clinical trial](https://jamanetwork.com/journals/jama/fullarticle/2702145).

Interpretation requires care. MERINO was open-label and stopped early, and its percentages are trial outcomes rather than predictions for an individual patient. A subsequent analysis using reference laboratory susceptibility testing narrowed the mortality difference and made it statistically uncertain. Nevertheless, IDSA continues to favor carbapenems for ESBL bloodstream infections because the overall evidence remains concerning for piperacillin-tazobactam. [IDSA treatment guidance](https://www.idsociety.org/practice-guideline/amr-guidance).

How does this evidence guide treatment today?

IDSA identifies meropenem, imipenem and ertapenem as preferred options for ESBL infections outside the urinary tract. It favors meropenem or imipenem in critical illness or when blood albumin is low. Piperacillin-tazobactam is not suggested for ESBL bloodstream infections even when laboratory testing reports susceptibility. After improvement, selected patients may transition to an oral antibiotic if testing confirms activity and their clinical circumstances support the change. [IDSA treatment guidance](https://www.idsociety.org/practice-guideline/amr-guidance).

This creates an important prescribing balance. Carbapenems can treat serious ESBL infections, but increasing reliance on them can encourage further resistance. Laboratory testing helps identify active treatment, while hand hygiene and infection prevention reduce opportunities for resistant bacteria to spread. The practical implication is to use an effective drug when a serious infection requires it while preventing avoidable infections and antibiotic exposure. [CDC ESBL treatment and prevention information](https://www.cdc.gov/esbl-producing-enterobacterales/about/).