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The BACTEC® MGIT™ 960 PZA Kit is used as a rapid qualitative procedure for susceptibility testing of Mycobacterium tuberculosis, from culture, to pyrazinamide (PZA). The BACTEC® MGIT™ 960 PZA kit is used with the BACTEC® MGIT™ 960 System.

The BACTEC® MGIT™ 960 PZA susceptibility test kit is used with the BACTEC® MGIT™ PZA Medium and performed on the BACTEC® MGIT™ 960 System. The PZA Medium tube is supplemented with BACTEC® MGIT™ 960 PZA Supplement and prepared with the appropriate dilution of pyrazinamide as the mechanism for performing the susceptibility test.

The BACTEC® MGIT™ 960 PZA susceptibility test utilizes a four to twenty-one day testing protocol. A standardized suspension of Mycobacterium tuberculosis growth is prepared from either solid or liquid culture media. An appropriate dilution is made of this suspension and 0.5 mL is inoculated into a Growth Control tube (drug-free) and a tube containing pyrazinamide (both tubes are referred to as an AST Set). The test interpretation is based on growth of the Mycobacterium tuberculosis isolate in the Growth Control tube compared to the growth in the drug-containing tube.

At the completion of the PZA susceptibility testing protocol. the instrument reports a susceptible or resistant result for the Mycobacterium tuberculosis isolate being tested.

The BACTEC® MGIT™ 960 PZA Kit is a medical device used for the rapid qualitative susceptibility testing of Mycobacterium tuberculosis to pyrazinamide (PZA) from culture. The device is used with the BACTEC® MGIT™ 960 System.

Acceptance Criteria and Device Performance

The acceptance criteria are implied through the comparison with a predicate device (BACTEC® 460TB PZA) and the achievement of high agreement percentages in various studies. The primary measure of performance is the "category agreement" with the reference method (BACTEC® 460TB PZA).

Study Details

2. Sample Size Used for the Test Set and Data Provenance:

• Analytical Study (Reproducibility): 26 qualified Mycobacterium tuberculosis strains (including 3 ATCC® strains).
• Analytical Study (CDC Challenge Panel): A panel of challenge strains from the Centers for Disease Control and Prevention (CDC).
• Clinical Studies (Reproducibility): A panel of five qualified strains.
• Clinical Studies (CDC Challenge Panel): A panel of challenge strains from the Centers for Disease Control and Prevention (CDC).
• Clinical Isolate Testing: A total of 118 clinical strains of Mycobacterium tuberculosis. This generated 228 PZA test results. The testing included fresh clinical and subculture isolates from both liquid and solid source cultures.
• Data Provenance: The clinical studies were conducted at four geographically diverse clinical sites, comprising regional reference centers and university-based laboratories. This suggests a prospective collection of data from various real-world clinical settings within the US (given the involvement of the CDC).

3. Number of Experts Used to Establish Ground Truth for the Test Set and Qualifications:
The document does not explicitly state the "number of experts" or their specific qualifications for establishing the ground truth. However, for the clinical isolate testing, the BACTEC® 460TB PZA test was used as the reference method. This implies that the results from the BACTEC® 460TB PZA, a legally marketed and established device, served as the ground truth. The CDC provides "expected results" for their challenge panels, indicating that their consensus or established laboratory findings were used as ground truth for those specific panels.

4. Adjudication Method for the Test Set:
The document does not describe a formal adjudication method (e.g., 2+1, 3+1). Instead, the performance of the BACTEC® MGIT™ 960 PZA was compared directly to the results obtained from either the "expected results" (for reproducibility and CDC challenge panels) or the "reference method" (BACTEC® 460TB PZA) for clinical isolate testing. Discrepancy resolution is not detailed.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study was done:
No, an MRMC comparative effectiveness study involving human readers improving with or without AI assistance was not performed. This device is an automated in vitro diagnostic test, not an AI-assisted diagnostic tool that would involve human interpretation of images or data.

6. If a Standalone Study (i.e., algorithm only without human-in-the-loop performance) was done:
Yes, the studies described are standalone performance evaluations of the BACTEC® MGIT™ 960 PZA Kit and system. The device automatically interprets results ("the instrument reports a susceptible or resistant result," "data are automatically interpreted by the instrument software"). While human operators are involved in preparing the samples and loading them into the instrument, the interpretation of the susceptibility result itself is automated by the device, making this a standalone performance assessment.

7. The Type of Ground Truth Used:

• Expected Results: For reproducibility testing (analytical and clinical) and CDC challenge panel testing (analytical and clinical), the "expected results" or "CDC expected results" were used as ground truth. These are likely established reference values for known strains.
• Reference Method: For the clinical isolate testing, the BACTEC® 460TB PZA test served as the reference method (ground truth). This implies that the results from an established and legally marketed predicate device were considered the correct outcome for comparison.

8. The Sample Size for the Training Set:
The document does not explicitly specify a "training set" size. The reported studies evaluate the performance of the device, implying that the algorithm and methodology were already developed. In vitro diagnostic devices like this typically undergo extensive development and internal testing, which would involve data, but it's not generally referred to as a "training set" in the context of reporting clinical validation for regulatory submission, as is common for AI/ML-based devices.

9. How the Ground Truth for the Training Set Was Established:
Since a "training set" is not explicitly mentioned in the context of this regulatory submission, how its ground truth might have been established is not described. The focus is on the validation of the final device against established methods and reference panels.

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