What is the Carbapenem (CARB) screening test?

From the Guidelines

The carbapenem screening test is used to detect carbapenemase-producing organisms, particularly in Enterobacteriaceae, and rapid testing should be used to identify specific carbapenemase families, such as KPC, NDM, VIM, and OXA-48-like, to guide treatment strategies 1.

Importance of Carbapenem Screening

The carbapenem screening test is crucial for infection control and guiding antibiotic therapy, as carbapenem resistance severely limits treatment options.

• The test helps identify carbapenemase-producing organisms, which typically require combination therapy with agents like polymyxins (colistin), tigecycline, or newer agents like ceftazidime-avibactam depending on the specific resistance mechanism identified.
• Positive results should prompt strict infection control measures and consultation with infectious disease specialists.

Methods for Carbapenem Screening

Several methods are available for carbapenem screening, including:

• The Modified Hodge Test (MHT), which is a common screening method where a lawn of susceptible E. coli is streaked on an agar plate, and a carbapenem disk is placed in the center.
• The Carba NP test, which detects pH changes when carbapenemases hydrolyze imipenem.
• Molecular tests that identify specific carbapenemase genes like KPC, NDM, and OXA-48. Rapid testing for specific carbapenemase families is strongly recommended to guide treatment strategies, with a strong recommendation and moderate certainty of evidence 1.

Clinical Implications

The carbapenem screening test has significant clinical implications, including:

• Guiding antibiotic therapy: The test helps identify the most effective treatment options for patients with carbapenem-resistant infections.
• Infection control: Positive results should prompt strict infection control measures to prevent the spread of carbapenem-resistant organisms.
• Consultation with infectious disease specialists: The test results should be discussed with infectious disease specialists to determine the best course of treatment. Although another study suggests detecting carbapenemases of CRE isolates can be achieved by phenotypic or genotypic test in healthcare facilities 1, the most recent and highest quality study recommends rapid testing for specific carbapenemase families to guide treatment strategies 1.

From the Research

Overview of the Carbapenem (CARB) Screening Test

• The Carbapenem (CARB) screening test is used to detect carbapenemase-producing organisms (CPO) in patients, which is crucial for infection control and prevention in healthcare settings 2, 3, 4.
• The Xpert Carba-R test is a rapid real-time quantitative PCR (qPCR) assay that can detect five families of carbapenemase genes (blaIMP, blaKPC, blaNDM, blaOXA-48, and blaVIM) directly from rectal swab specimens 4.

Methodology and Performance

• The Xpert Carba-R test has been evaluated in several studies, demonstrating high sensitivity and specificity for detecting carbapenem resistance genes 2, 4.
• A pooling strategy using the Xpert Carba-R test has been shown to be effective for screening multiple specimens, with significant cost savings 2.
• The test has a positive percentage of agreement (PPA) between 60 and 100% for four targets (blaKPC, blaNDM, blaVIM, and blaOXA-48) and a negative percentage of agreement (NPA) ranging between 98.9 and 99.9% relative to the reference method (culture and sequencing of any carbapenem-nonsusceptible isolate) 4.

Clinical Applications and Risk Factors

• The Carbapenem (CARB) screening test is used to identify patients at risk of carrying CPO, which is essential for preventing the spread of these organisms in healthcare facilities 3, 5.
• Risk factors for infection or colonization with carbapenem-resistant Enterobacteriaceae (CRE) include the use of fluoroquinolones and cephalosporins, as well as undergoing invasive procedures with a scope device 5.
• The test can be used to guide infection control measures and antibiotic stewardship programs in healthcare settings 3, 5.