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The AmpliVue® GBS Assay is a qualitative in vitro diagnostic test for the rapid detection of Group B Streptococcus from vaginal/rectal swabs from antepartum women following 18 to 24 hours of incubation in an LIM enrichment broth culture. The AmpliVue" GBS Assay utilizes helicase-dependent amplification (HDA) of the thiolase (atoB) gene sequence and a self-contained disposable amplification detection device that allows for manual evaluation of assay results. Results can be used as an aid in determining the colonization status of antepartum women.

The AmpliVue GBS Assay does not provide susceptibility results. Culture isolates are needed for performing susceptibility testing as recommended for penicillin-allergic women.

The AmpliVue® GBS Assay is intended for use in hospital, reference or state laboratory settings. The device is not intended for point-of-care use.

The AmpliVue® GBS Assay combines simple sample processing, an isothermal amplification technology named helicase-dependent amplification (HDA), and a selfcontained disposable amplicon detection device, for the detection of Group B Streptococcus from vaginal /rectal swabs following 18 to 24 hours incubation in Lim enrichment broth culture.

A small amount of cultured specimen is transferred into a dilution tube. The diluted sample culture is then transferred into a lysis tube, and the cells are lysed by simple heat treatment. After heat treatment, an aliquot of the lysed sample is added to a reaction tube containing a lyophilized mix of HDA reagents including primers specific for the amplification of the thiolase (atoB) gene. The rationale behind the selection of this particular target sequence were: 1) a BLAST search of this gene resulted in no thiolase with significant homology in species other than those belonging to S. agalactiae; 2) the gene is conserved in GBS based on the recent GBS Genome project. The assay also includes a process control that monitors sample processing, confirms the integrity of the assay reagents and cassette detection, and assays for HDA-inhibitors that may be present within a broth culture. After completion of the HDA reaction, the reaction tube is transferred to a cassette for rapid detection with test result displayed as test and/or control lines in the window of the cassette.

Here's a breakdown of the acceptance criteria and study details for the AmpliVue® GBS Assay, based on the provided 510(k) summary:

Acceptance Criteria and Device Performance

1. Table of Acceptance Criteria and Reported Device Performance:

The document doesn't explicitly state "acceptance criteria" in a separate table with target values for clinical performance. However, it presents the clinical sensitivity and specificity results. For the purpose of this response, we'll interpret the reported clinical performance metrics as reflecting the achieved acceptance criteria. The predicate device's performance is also included for context, as it would have likely informed the expected performance of the new device.

Note: The document explicitly states "Reproducibility studies are acceptable" without providing a numerical acceptance criterion. For clinical sensitivity and specificity, no explicit numerical acceptance criterion is provided for the AmpliVue® GBS Assay in this summary. Instead, its performance is presented, and it is also compared to the predicate device's clinical sensitivity.

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

• Sample Size for Clinical Study (Test Set): 911 specimens were initially collected. After accounting for invalid samples (3 initially, 3 remaining invalid after repeat testing), the clinical performance was calculated based on 908 specimens.

• Data Provenance:

  • Country of Origin: United States (four distinct geographical sites).
  • Retrospective or Prospective: Prospective study conducted from July to November 2013.

• Sample Size for Analytical Studies (LoD, Cross-reactivity, Interference, Inclusivity):

  • LoD: For each of the six GBS strains, 20 replicates were tested, across 5 experiments of 14 assays per strain.
  • Cross-reactivity: Two GBS strains (BAA-611 and SS617) tested near LoD alongside a panel of 91 organisms (76 bacteria, 3 yeast, 11 viruses, 1 parasite) and human genomic DNA.
  • Interference: Two GBS strains (BAA-611 and SS617) tested near LoD with a panel of 34 substances.
  • Inclusivity: Twelve additional strains of Streptococcus agalactiae were tested as three replicates each, near the LoD.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications:

The document does not explicitly state the "number of experts" used to establish the ground truth or their specific qualifications (e.g., "radiologist with 10 years of experience").

However, the ground truth for the clinical study was established by bacterial culture. This implies that laboratory professionals (e.g., microbiologists, medical technologists) followed established protocols for bacterial culture, which serves as the "gold standard" or ground truth for GBS detection in this context.

For discordant specimens (AmpliVue Positive/Bacterial Culture Negative, and AmpliVue Negative/Bacterial Culture Positive), an FDA-cleared molecular device for the detection of GBS was used for further testing. This implies that the results from this FDA-cleared molecular device were leveraged to refine the understanding of the true GBS status in these cases.

4. Adjudication Method for the Test Set:

Based on the information provided, the adjudication method for the clinical test set seems to be:

• Primary Ground Truth: Bacterial culture.
• Discordant Analysis: For specimens where the AmpliVue® GBS Assay and bacterial culture disagreed, an FDA-cleared molecular device for the detection of GBS was used to re-evaluate the specimen. The results from this molecular device were then factored into the final assessment of the true positive/negative status for the discordant samples, as indicated by the footnotes in the clinical performance table. For example, of the 52 AmpliVue Positive/Bacterial Culture Negative samples, 39 were determined positive by the FDA-cleared molecular device. Similarly, the 1 AmpliVue Negative/Bacterial Culture Positive sample was found negative by the FDA-cleared molecular device.

This method resembles a tie-breaker or reference method adjudication rather than an expert consensus voting system.

5. 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 was not done.

This device is an in vitro diagnostic (IVD) assay for direct detection of a pathogen, not an AI-powered diagnostic imaging tool that assists human readers. Therefore, the concept of "human readers improve with AI vs without AI assistance" is not applicable to this type of device. The assay results are read manually (colored lines visible to the naked eye) by a single operator for each test, rather than a panel of human readers interpreting complex medical images.

6. If a Standalone (i.e. algorithm only without human-in-the-loop performance) was Done:

The performance reported in the clinical study (Clinical Sensitivity and Specificity) is a standalone performance of the AmpliVue® GBS Assay. The assay produces a direct result (test and/or control lines in the cassette window visible to the naked eye) that is interpreted by an operator. While an operator reads the result, it's not a "human-in-the-loop" scenario in the sense of a subjective interpretation or decision-making process that would significantly alter the algorithm's output. The output of the HDA reaction and detection cassette directly provides the positive/negative result.

7. The Type of Ground Truth Used (expert consensus, pathology, outcomes data, etc.):

The primary ground truth used for the clinical study was bacterial culture, which is the conventional gold standard for confirming GBS colonization. For discordant results, further confirmation was sought using an FDA-cleared molecular device for the detection of GBS.

8. The Sample Size for the Training Set:

The document does not provide information on a specific "training set" sample size. This is common for molecular diagnostic assays that detect specific gene sequences. The assay's "training" largely relies on the initial design and optimization of primers, probes, and reaction conditions to target the specific atoB gene sequence of S. agalactiae based on existing genomic knowledge. The clinical studies and performance evaluations described are validation studies, not "training" of a machine learning model.

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

As there is no explicit "training set" in the context of machine learning, the question of how its ground truth was established is not directly applicable.

However, the design of the assay (selection of the atoB gene as a target) was based on:

• BLAST search indicating no significant homology in non-S. agalactiae species.
• Conservation of the gene in GBS based on the recent GBS Genome project.

These bioinformatics and genomic reference data can be considered the "ground truth" that informed the initial assay design and target selection. The analytical and clinical validation studies then confirm that this design effectively detects GBS in real-world samples.

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