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The Xpert Xpress CoV-2 plus test, performed on the GeneXpert Xpress System, is a rapid real-time RT-PCR test intended for the qualitative detection of SARS-CoV-2 RNA in nasopharyngeal and anterior nasal swab specimens collected from individuals with signs and symptoms of respiratory tract infection.

The Xpert Xpress CoV-2 plus test is intended for use as an aid in the diagnosis of COVID-19 if used in conjunction with other clinical, epidemiologic, and laboratory findings. Positive results are indicative of the presence of SARS-CoV-2 RNA. Positive results do not rule out bacterial infection or co-infection with other pathogens.

Negative results do not preclude SARS-CoV-2 infection. The results of this test should not be used as for diagnosis and patient management decisions.

The Xpert Xpress CoV-2 plus test is a rapid, automated in vitro diagnostic test for the qualitative detection of viral RNA from SARS-CoV-2 in nasopharyngeal swab (NPS) and anterior nasal swab (NS) specimens collected from individuals with signs and symptoms of respiratory tract infection.

The Xpert Xpress CoV-2 plus test is performed on GeneXpert Xpress System, which consist of a GeneXpert IV instrument that executes sample preparation, nucleic acid amplification and real-time fluorescent signal detection for the tests, and a GeneXpert Hub with preloaded GeneXpert Xpress software for running the tests and viewing the test results. The GeneXpert Hub accessory integrates the computer, touchscreen monitor and barcode scanner. Each of the GeneXpert modules in the GeneXpert IV instrument can perform independent sample preparation and testing. The GeneXpert Xpress System requires the use of single-use disposable cartridges that hold the RT-PCR reagents and host sample purification, nucleic acid amplification, and detection of the target sequences. Because the cartridges are selfcontained, cross-contamination between samples is minimized.

The Xpert Xpress CoV-2 plus test includes reagents for the detection of viral RNA from SARS-CoV-2 in NPS and NS specimens. The primers and probes in the Xpert Xpress CoV-2 plus test are designed to amplify and detect unique sequences in the genes that encode the following SARS-CoV-2 proteins: nucleocapsid (N2), envelope (E), and RNA-dependent RNA polymerase (RdRP). A Sample Processing Control (SPC) and a Probe Check Control (PCC) are also included in the cartridge serving as internal controls. The SPC is present to control for adequate processing of the sample and to monitor for the presence of potential inhibitor(s) in the RT-PCR reaction. The SPC also ensures that the RT-PCR reaction conditions (temperature and time) are appropriate for the amplification reaction and that the RT-PCR reagents are functional. The PCC verifies reagent rehydration, PCR tube filling, and confirms that all reaction components are present in the cartridge including monitoring for probe integrity and dye stability.

The Xpert Xpress CoV-2 plus test is designed for use with NPS or NS specimen collected with nylon flocked swabs and placed into viral transport medium (VTM), Universal Transport Medium (UTM) or eNAT®.

Acceptance Criteria and Study for Xpert Xpress CoV-2 plus

The Xpert Xpress CoV-2 plus test is a rapid real-time RT-PCR test for the qualitative detection of SARS-CoV-2 RNA in nasopharyngeal and anterior nasal swab specimens. The study aims to demonstrate substantial equivalence to a predicate device (K230440) by evaluating its analytical and clinical performance.

1. Table of Acceptance Criteria and Reported Device Performance

2. Sample Sizes and Data Provenance

• Test Set (Clinical Performance):

  • Total specimens: 1783
    • NPS (Nasopharyngeal Swab): 883
    • NS (Anterior Nasal Swab): 900
  • Data Provenance: Prospective clinical specimens collected from individuals showing signs and symptoms of respiratory infection in the United States (22 geographically diverse CLIA-waived sites). Data was collected in 2022.

• Analytical Performance Test Sets:

  • Limit of Detection (LoD):
    • NPS-UTM/VTM: At least 40 replicates (2 reagent lots x 20 replicates)
    • NPS-eNAT: At least 40 replicates (2 reagent lots x 20 replicates)
    • NS-UTM/VTM: At least 40 replicates (2 reagent lots x 20 replicates)
    • WHO First International Standard (NS-UTM/VTM): 20 replicates
  • Analytical Reactivity (Wet-testing): 61 SARS-CoV-2 strains, 3 replicates per strain (total 183 tests).
  • Analytical Specificity (Wet-testing): 62 microorganisms, 3 replicates per organism (total 186 tests).
  • Microbial Interference: 18 commensal microorganisms, 8 replicates per strain (total 144 tests) with SARS-CoV-2.
  • Potentially Interfering Substances: 23 substances, 8 replicates for negative samples and 8 replicates for positive samples (total up to 368 tests, plus re-tests).
  • Carryover Contamination: 40 positive samples, 42 negative samples.
  • Reproducibility: 3 panel members (Negative, Low Pos, Mod Pos), 90 observations per panel member (3 Sites x 3 Operators x 1 Lot x 5 Days x 1 Run x 2 Replicates = 90). Total 270 observations.

3. Number of Experts and Qualifications for Ground Truth (Test Set)

The document does not explicitly state the number of experts used to establish the ground truth for the clinical test set or their specific qualifications (e.g., radiologist with 10 years of experience). However, the ground truth was established by a "U.S. FDA-cleared molecular respiratory panel that included SARS-CoV-2," indicating an established and validated laboratory method. Discrepant results were investigated using a "U.S FDA EUA SARS-CoV-2 molecular test," further relying on FDA-authorized assays as the reference standard.

4. Adjudication Method (Test Set)

The adjudication method used for the clinical test set was a discrepant analysis. "Discrepant results between Xpert Xpress CoV-2 plus and the comparator were investigated using a U.S FDA EUA SARS-CoV-2 molecular test." This implies that for any cases where the Xpert Xpress CoV-2 plus result differed from the initial FDA-cleared comparator panel, a third, independent FDA EUA molecular test was used to determine the true positive or negative status.

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

There is no MRMC comparative effectiveness study mentioned in the provided text. The study focuses on the standalone performance of the device against a comparator device, not on human reader performance with or without AI assistance.

6. Standalone Performance Study

Yes, a standalone performance study was done. The entire "Performance Studies" section (1.4) details the analytical and clinical performance of the device itself (algorithm only, without human-in-the-loop performance). The clinical performance evaluation directly compares the Xpert Xpress CoV-2 plus test results to those of an FDA-cleared molecular respiratory panel.

7. Type of Ground Truth Used

For the clinical performance study, the ground truth was established by an FDA-cleared molecular respiratory panel and, in cases of discrepancy, by a U.S. FDA EUA SARS-CoV-2 molecular test. This falls under the category of reference standard laboratory testing rather than expert consensus, pathology, or outcomes data.

For analytical performance studies, the ground truth was established by spiking known concentrations/quantities of inactivated SARS-CoV-2 virus, genomic RNA, or other microorganisms into negative matrices, or by using established international standards (e.g., WHO First International Standard).

8. Sample Size for the Training Set

The document does not mention the sample size for the training set. This is a premarket notification (510(k)) and focuses on the performance testing of the final device, not on the developmental or training phases of its underlying algorithm. As a PCR-based diagnostic, it's unlikely to have a "training set" in the same sense as an AI/ML-based device; its analytical performance is determined by the specific primers and probes and their chemical/biological interactions.

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

Since no "training set" is explicit for this PCR diagnostic, there is no information provided on how its ground truth might have been established. The development of PCR assays typically involves careful design and validation of primers and probes against known genomic sequences and wet-lab testing with characterized samples, rather than machine learning training on a dedicated dataset.

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