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The Xpert GBS LB XC test, performed on the GeneXpert® Instrument Systems, is an automated qualitative in vitro diagnostic test for the detection of Group B Streptococcus (GBS) DNA from enriched vaginal/rectal swab specimens, using real- time polymerase chain reaction (PCR).

Xpert GBS LB XC testing is indicated as an aid in determining the GBS colonization status of antepartum women.

· The Xpert GBS LB XC test is intended for antepartum testing on enriched Lim broth cultures of vaginal/rectal swabs after 18-24 hours of incubation

· The Xpert GBS LB XC test does not provide antimicrobial susceptibility test results. Culture is necessary to obtain isolates to perform susceptibility testing as recommended for penicillin-allergic women

The Xpert GBS LB XC test is an automated in vitro diagnostic test for qualitative detection of DNA from Group B Streptococcus (GBS) from vaginal-rectal swab specimens obtained from pregnant women that are transported to the laboratory following enrichment in Lim broth.

The primers and probes in the Xpert GBS LB XC test are designed to simultaneously amplify and detect two unique GBS chromosomal targets: the first is a target within a coding region for a glycosyl transferase family protein and the second is within a coding region for a LysR family transcriptional regulator of Streptococcus agalactiae DNA.

The Xpert GBS LB XC test includes reagents for the detection of DNA from GBS in Lim broth-enriched vaginal/rectal swabs. A Sample Processing Control (SPC) and a Probe Check Control (PCC) are also included in the cartridge. The SPC is present to control for adequate extraction and processing of the target sequences and to monitor for the presence of inhibitors in the PCR reaction. The PCC verifies reagent rehydration, PCR tube filling in the cartridge, probe integrity, and dve stability.

The single-use, multi-chambered fluidic cartridges are designed to complete sample preparation and real-time PCR for the detection of GBS genomic DNA in as little as 27 minutes with high titer specimens; GBS negative specimens generate results in approximated 43 minutes. The GeneXpert Instrument Systems, comprised of the GeneXpert Dx Systems and the GeneXpert Infinity Systems, have 1 to 80 randomly accessible modules, depending upon the instrument, that are each capable of performing separate sample preparation and real-time PCR and RT-PCR tests. Each module contains a syringe drive for dispensing fluids (i.e., the syringe drive activates the plunger that works in concert with the rotary valve in the cartridge to move fluids between chambers), an ultrasonic horn for lysing cells or spores, and a proprietary I-CORE® thermocycler for performing real-time PCR and RT-PCR and detection.

The Xpert GBS LB XC test is performed on the Cepheid GeneXpert® Instrument Systems (GeneXpert Dx, GeneXpert Infinity-48s, and GeneXpert Infinity-80 systems). The GeneXpert Instrument System platform automates sample preparation, amplification and real-time detection. The GeneXpert systems consist of an instrument, computer, and preloaded software for running tests and viewing the results.

The GeneXpert Instrument Systems require the use of single-use, disposable cartridges (the Xpert GBS LB XC cartridges) that hold the PCR reagents and host the PCR process. Because the cartridges are self-contained and specimens never come into contact with working parts of the instrument modules, cross-contamination between samples is minimized.

Here's a breakdown of the acceptance criteria and the study proving the device meets them, based on the provided text:

Acceptance Criteria and Reported Device Performance

The document describes the performance of the Xpert GBS LB XC test, a qualitative in vitro diagnostic test for the detection of Group B Streptococcus (GBS) DNA. The acceptance criteria are implicitly derived from the reported performance characteristics.

Study Details

1. Sample size used for the test set and the data provenance:

   • Test Set Sample Size: 621 specimens were included in the Xpert GBS LB XC versus Composite Comparator analysis.
   • Data Provenance: The study was a multi-site clinical study conducted in the United States. It used vaginal/rectal swab specimens collected from pregnant females as part of routine care. The nature of the specimen collection ("as a part of routine care") suggests it was likely a prospective collection for this study, though it might have utilized leftover samples. The text specifies "aliquots of leftover Lim broth samples were obtained for testing."

2. Number of experts used to establish the ground truth for the test set and the qualifications of those experts:

   • The document does not specify the number of experts or their qualifications for establishing the ground truth. The ground truth was established using a "composite comparator method" which involved enriched bacterial culture and an FDA cleared NAAT. For the culture component, species identification was performed via Matrix Assisted Laser Desorption Ionization - Time of Flight Mass Spectroscopy (MALDI-TOF MS). While MALDI-TOF MS requires skilled lab personnel, the term "expert" in the sense of a medical professional making a diagnostic determination is not used for this ground truth establishment.

3. Adjudication method (e.g. 2+1, 3+1, none) for the test set:

   • The adjudication method for the test set was: "a specimen was considered positive if either enriched bacterial culture or the FDA cleared NAAT was positive and negative when both enriched bacterial culture and the FDA cleared NAAT were negative." This is a rule-based composite comparator rather than an expert adjudication method like 2+1.

4. If a multi reader multi case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance:

   • No, a multi-reader multi-case (MRMC) comparative effectiveness study focusing on human readers improving with AI assistance was not done. This device is an automated in vitro diagnostic test (NAAT) for detecting GBS DNA. It does not involve human "readers" in the diagnostic process beyond laboratory technicians operating the equipment and interpreting the automated qualitative results.

5. If a standalone (i.e. algorithm only without human-in-the loop performance) was done:

   • Yes, the clinical "Performance of Xpert GBS LB XC v Composite Comparator" (Table 9) is a standalone performance assessment. The Xpert GBS LB XC test is an automated qualitative test where the instrument system performs sample preparation, amplification, and real-time detection, with the software running tests and viewing results. This is inherently an "algorithm only" performance, as the final output is a qualitative (Positive/Negative) result generated by the device itself.

6. The type of ground truth used (expert consensus, pathology, outcomes data, etc):

   • A composite comparator method was used as the ground truth. This method combined:
     • Enriched bacterial culture with species identification via Matrix Assisted Laser Desorption Ionization - Time of Flight Mass Spectroscopy (MALDI-TOF MS).
     • An FDA cleared Nucleic Acid Amplification Test (NAAT).

7. The sample size for the training set:

   • The document describes a clinical validation study for regulatory submission. It does not provide information about the sample size used for the training set of the algorithm or device. Regulatory submissions typically focus on validation performance rather than development/training data.

8. How the ground truth for the training set was established:

   • Since information on the training set (including its sample size) is not provided, the method for establishing its ground truth is also not detailed in this document.

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