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NG-Test® CTX-M MULTI is an in vitro rapid and visual immunochromatographic assay for the qualitative detection of CTX-M enzymes (groups 1, 2, 8, 9, and 25) from pure colonies of Enterobacterales suspected of ESBL production when grown on the following media:

• 5% sheep blood agar or MacConkey agar (16-24 hours)
• HardyCHROM™ ESBL agar (18-24 hours)

The NG-Test® CTX-M MULTI is intended as an aid for infection control in the detection of CTX-M enzymes-producing organisms (Enterobacterales) in healthcare settings. NG-Test® CTX-M MULTI is not intended to guide or monitor treatment. A positive or negative NG-Test® CTX-M MULTI test result does not rule out the presence of other mechanisms of antibiotic resistance. NG-Test® CTX-M MULTI should be used in conjunction with other laboratory tests including phenotypic antimicrobial susceptibility testing.

NG-Test® CTX-M MULTI is an in vitro rapid and visual immunochromatographic assay for the qualitative detection of CTX-M enzymes (groups 1, 2, 8, 9, and 25) from pure colonies of Enterobacterales suspected of ESBL production after culturing on agar and processed in an extraction buffer. The device consists of a sample port, sample and conjugate pad, and nitrocellulose test strip, which are contained within a plastic cassette, in addition to reagents for liquid extraction. The result can be read 15 minutes after adding the sample to the sample well. A positive result on the NG-Test® CTX-M MULTI occurs when two red lines appear, one on the control (C) region and one on the test (T) region. A negative result occurs when only the control line is observed and indicates the sample does not contain any target CTX-M enzymes, or the CTX-M enzymes are present at a non-detectable level. If the control line does not appear, the test result is invalid.

Monoclonal antibodies that recognize the five major CTX-M groups are immobilized on a nitrocellulose membrane. Free monoclonal antibodies are present in the conjugate pad and labeled with colloidal gold. Upon addition of the processed sample to the sample pad, the capillary action of the nitrocellulose draws the sample through the mobile antibodies in the conjugate pad and the immobile antibodies on the test strip. The immobilized control antibodies capture any mobile antibodies that do not bind to the test line.

This document describes the performance of the NG-Test® CTX-M MULTI device, an in vitro rapid immunochromatographic assay for detecting CTX-M enzymes.

Here is a breakdown of the requested information:

1. Acceptance Criteria and Reported Device Performance

The acceptance criteria for the device are implied by the reported sensitivity and specificity values. While explicit "acceptance criteria" are not listed as target percentages, the study results demonstrate high performance that led to clearance.

Table of Performance Data (Clinical Study - Blood and MacConkey Agar):

Table of Performance Data (Seeded Study - HC ESBL Agar):

Note: The lower bound of the specificity for HC ESBL agar (87.9%) is acknowledged as being below 90% due to a lower quantity of CTX-M negative isolates in this specific part of the study, and additional CTX-M negative isolates were evaluated in the cross-reactivity study to compensate.

2. Sample Size and Data Provenance

• Test Set Sample Size:
  • Clinical Study (Blood and MacConkey Agar): 309 Enterobacterales isolates.
  • Seeded Study (HardyCHROM™ ESBL Agar): 193 clinical isolates.
• Data Provenance:
  • Country of Origin: Not explicitly stated, but the study was conducted at "three geographically diverse hospitals," implying the data is from a clinical setting.
  • Retrospective or Prospective: A mix was used:
    • "Prospectively-collected" bacterial isolates were used for the performance evaluation.
    • "Stock bacterial isolates" were also used. This suggests a combination of prospective collection and retrospective use of archived isolates.

3. Number of Experts and Qualifications for Ground Truth

• The document does not specify the number of experts used to establish ground truth or their qualifications. The ground truth relies on laboratory methods (PCR and AST).

4. Adjudication Method for the Test Set

• The document does not describe an adjudication method for the test set results. The comparison is between the device's reading and the reference method (PCR and AST).

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

• A MRMC comparative effectiveness study involving human readers with vs. without AI assistance was not conducted. This device is an immunochromatographic assay, not an AI-based diagnostic with human-in-the-loop performance.
• However, a reproducibility study involved multiple readers: "The testing was done with one operator and two readers, blinded to each other's results, per site." This was to demonstrate reproducibility of the device's results, not to compare human performance with and without the device.

6. Standalone (Algorithm Only) Performance

• This device is a standalone diagnostic test (an immunochromatographic assay). Its performance is evaluated directly without a human-in-the-loop component for result interpretation beyond visual reading. The reported sensitivity and specificity refer to the device's performance as a standalone test.

7. Type of Ground Truth Used

• Reference standard:
  • PCR (Polymerase Chain Reaction): Used to detect blaCTX-M genes, considered the definitive molecular method. Isolates with a positive PCR result were also sequenced to determine the CTX-M variant.
  • Antimicrobial Susceptibility Testing (AST): Performed according to CLSI M100, 34th edition breakpoints. A positive comparator method result was defined as any Enterobacterales that produced a positive PCR result and was not susceptible to at least one of the antimicrobial agents.
  • Identification (ID): Performed using FDA-cleared ID systems.

8. Sample Size for the Training Set

• The document does not specify a separate "training set" size. As this is an immunochromatographic assay, it doesn't involve machine learning model training in the typical sense. The analytical reactivity study and analytical specificity study essentially serve as extensive performance characterization using known strains, which could be conceptually similar to a "development" or "characterization" set for more traditional devices.
  • Analytical Reactivity: 57 strains of Enterobacterales characterized to harbor CTX-M enzymes.
  • Analytical Specificity: 55 organisms with other resistance mechanisms.

9. How the Ground Truth for the Training Set Was Established

• For the analytical reactivity and analytical specificity studies (which characterize the device's performance with known strains, akin to a training/development set in ML contexts):
  • Strains were "characterized to harbor CTX-M enzymes" or "exhibit antimicrobial resistance mechanisms other than CTX-M." This characterization would typically involve established molecular methods (e.g., PCR, sequencing) and phenotypic susceptibility testing performed by a reference lab or research institution. The document states "Each organism was incubated..." and tested, implying these were well-characterized isolates.

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