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The Great Basin Shiga Toxin Direct Test performed on the Portrait™ Analyzer is an automated, in vitro diagnostic assay for the qualitative detection of Shiga toxin 1 (stxl) / Shiga toxin 2 (stx2) genes and specific identification of a conserved genetic region of the E. coli O157 serogroup. Shiga toxin genes are found in Shiga toxin-producing strains of E. coli (STEC) and Shigella dysenteriae. The E. coli 0157 test result is reported only if a Shiga toxin gene is also detected.

The test is performed directly from Cary-Blair or C&S Medium preserved stool specimens from symptomatic patients with suspected acute gastroenteritis, or colitis in hospital laboratories. The assay is intended for use in conjunction with clinical presentation as an aid in the diagnosis of STEC infections. Positive results do not rule out oninfection with other organisms, and may not be the definitive cause of patient illness.

The results of this test should not be used as the sole basis for diagnosis, treatment, or other patient management decisions. Shiga Toxin Direct Test negative results in the setting of clinical illness compatible with gastroenteritis may be due to infection by pathogens that are not detected by this test or non-infectious causes such as ulcerative colitis, irritable bowel syndrome, or Crohn's disease.

The Portrait System is a fully automated system that includes the Portrait Analyzer, single-use Great Basin Shiga Toxin Direct Test cartridges, and the Portrait System data analysis software. The Portrait System is designed to perform automated sample preparation, PCR, and optical chip-based detection with integrated data analysis in approximately 2 hours.

The single-use Test Cartridge contains blister packs, fluidic channels, processing chambers, a waste chamber, and an assay chip coated with an array of sequence-specific detection probes. All reagents are contained within the integrated blister packs with the exception of the amplification reagents and SPC, which are dried into the Amplification Chamber and SPC Chambers of the Cartridge, respectively.

The appropriate specimen for use in the Test Cartridge is an aliquot of stool from symptomatic patients preserved in Cary-Blair or C&S transport media. A preserved stool specimen is placed into the sample port of the Test Cartridge for processing. Multiple fluidic channels move reagents from integrated blister packs to chambers where reagent mixing and sample processing occur. A waste chamber, self-contained and segregated within the Test Cartridge, collects and stores reagent waste.

Here's a breakdown of the acceptance criteria and study details for the Great Basin Shiga Toxin Direct Test, as extracted from the provided text:

1. Table of Acceptance Criteria and Reported Device Performance:

The document doesn't explicitly state "acceptance criteria" as a separate, pre-defined set of values that the device must meet to be approved. Instead, it presents the clinical performance (sensitivity, specificity, PPA, NPA) as results from the studies, which are then compared to a predicate device (though specific performance metrics for the predicate are noted as "Not Reported").

However, based on the performance data presented, here's a summary of the device's reported performance which implicitly serve as the achieved acceptance level, especially when compared against itself in different study types. The comparison chart with the predicate device also indicates a qualitative "same" for intended use and target sequences which are fundamental acceptance points.

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

• Prospective Clinical Study:

  • Sample Size: 1,082 clinical specimens.
  • Data Provenance:
    • Origin: Collected prospectively (fresh) at five sites.
    • Retrospective/Prospective: Prospective.
    • Timeframe: June to September 2015 (three-month period).

• Frozen Retrospective Clinical Study:

  • Sample Size: 88 unique frozen clinical specimens (from an initial panel of 92).
  • Data Provenance:
    • Origin: Previously characterized clinical specimens.
    • Retrospective/Prospective: Retrospective.

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

The document does not specify the number of experts used or their qualifications to establish the ground truth for the clinical test sets. It mentions "reference clinical microbiology protocols" for the prospective study and "Clinical Characterization - Molecular and/or Shiga Toxin EIA" for the retrospective study as the basis for ground truth.

4. Adjudication Method for the Test Set:

The document does not detail any specific adjudication method (e.g., 2+1, 3+1). It states that the device's performance was compared to "reference clinical microbiology protocols" and "Molecular and/or Shiga Toxin EIA" results. For discrepant results in the prospective study, it notes:

• "Shiga toxin was detected in 8/8 false positive specimens by both bi-directional sequencing and alternate, FDA-cleared comparator NAAT."
• "O157 serogroup was detected in 2/2 false positive specimens by alternate, FDA-cleared comparator NAAT."
  This describes a characterization process for disagreements rather than a multi-expert adjudication method for the initial ground truth.

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:

This device is an in-vitro diagnostic assay for direct detection of nucleic acids, not an imaging device or an AI-assisted diagnostic tool that involves human readers. Therefore, an MRMC comparative effectiveness study involving human readers and AI assistance is not applicable and was not performed.

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

Yes, the studies evaluate the Great Basin Shiga Toxin Direct Test (a molecular diagnostic assay run on an automated system) as a standalone device. The device's output (qualitative detection of Shiga toxin genes and E. coli O157) is the primary subject of the performance evaluation. It is an automated, in-vitro diagnostic assay.

7. The Type of Ground Truth Used:

• Prospective Clinical Study: "Reference clinical microbiology protocols for the detection of both Shiga Toxin and the E. coli O157 Serotype." This typically involves culture, immunoassay (EIA), and potentially molecular methods. For discrepant results, bi-directional sequencing and FDA-cleared comparator NAAT were used for confirmation.
• Frozen Retrospective Clinical Study: "Clinical Characterization - Molecular and/or Shiga Toxin EIA."

8. The Sample Size for the Training Set:

The document does not explicitly mention a "training set" in the context of machine learning or AI algorithm development because this is a molecular diagnostic test. However, the document details various analytical studies which are foundational to the device's design and calibration. These studies use panels of known strains and concentrations:

• Analytical Sensitivity (LoD): Involved testing specific E. coli strains (ATCC BAA-2191, ATCC 51434, ATCC BAA-2192, ATCC 43895) at varying concentrations (e.g., 25/25, 21/22, 26/26, 20/20 correct results for LoD determination, indicating numerous replicates).
• Analytical Reactivity (Inclusivity): Tested 33 known positive strains (30 STEC, 3 Shigella dysenteriae) with 3 replicates each, totaling 99 tests.
• Analytical Specificity (Exclusivity): Tested 118 microorganisms (bacteria, fungi, yeasts, parasites, viruses) and human genomic DNA, each typically with 3 replicates (e.g., 3/3 results mentioned frequently).
• Microbial Interference: Tested 42 microorganisms, each typically with 3 or more replicates, against two STEC strains (ATCC 43895 and ATCC 43894) at 2X LoD.
• Interfering Substances: Tested 26 different substances, each with 3 replicates, in both positive and negative stool matrices.

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

For these analytical studies, the ground truth was established by using well-characterized reference strains (e.g., ATCC strains) with known genetic profiles (presence of stx1, stx2, O157 genes) and established concentrations. This allows for precise control and verification of the device's ability to detect specific targets and its limits of detection, and to ensure it does not cross-react with non-targets. For other studies like specimen stability, known positive samples were contrived by spiking these characterized strains into negative stool matrix.

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The Great Basin Portrait™ GBS Assay, performed on the PA500 Portrait™ Analyzer System, is a qualitative in vitro diagnostic test (IVD) for the detection of Group B Streptococcus (GBS) DNA from vaginal/rectal swabs from antepartum women, following enrichment in LIM Broth for 18 - 29 hours. The assay utilizes automated sample preparation and polymerase chain reaction (PCR) to amplify a cfb gene sequence specific to the Streptococcus agalactiae (GBS) genome which is detected by hybridization probes immobilized on a silica chip surface.

Results from the Portrait™ GBS Assay can be used as an aid in determining colonization status in antepartum women. The Portrait™ GBS Assay does not provide susceptibility results. Cultured isolates are needed for performing susceptibility testing as recommended for penicillin-allergic women.

The Portrait™ GBS Assay is intended for use in clinical laboratory, and reference laboratory settings. The Portrait™ GBS Assay is not intended for point of care use.

The Great Basin PA500 Portrait Analyzer System is a fully automated system that includes the Portrait Analyzer, single-use Portrait GBS Assay Test Cartridges, and the Portrait data analysis software. The PA500 Portrait Analyzer System is designed to perform automated sample preparation, PCR, and optical chip-based detection with integrated data analysis in approximately 90 minutes. The Great Basin Portrait™ GBS Assay utilizes automated hot-start PCR technology to amplify target nucleic acid sequences that are detected using species-specific S. agalactiae DNA hybridization probes immobilized on a modified silicon chip surface.

Here's a breakdown of the acceptance criteria and the study details for the Portrait™ GBS Assay based on the provided document:

Acceptance Criteria and Reported Device Performance

Device Name: Portrait™ GBS Assay

Note: The document does not explicitly state pre-defined acceptance criteria values for sensitivity, specificity, PPV, or NPV in the "510(k) Summary" section. Instead, these are presented as the "overall assay performance" observed during the clinical study.

Study Details

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

• Sample Size: 448 compliant clinical samples.
• Data Provenance: From three clinical sites in the United States. The study was prospective, as samples were "run over the course of four months to evaluate the performance."

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

• The document states that the Portrait™ GBS Assay performance was compared "to the reference GBS clinical microbiology protocol." This implies standard laboratory culture methods were used as the gold standard. There is no mention of human experts establishing the ground truth for the test set in this context.

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

• None explicitly mentioned as human adjudication; the reference standard was the "GBS clinical microbiology protocol" (culture).

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, an MRMC comparative effectiveness study involving human readers and AI assistance was not performed or described. This device is an in vitro diagnostic (IVD) assay for molecular detection, not an AI-powered image analysis or diagnostic support tool for human readers.

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

• Yes, the clinical performance study evaluated the Portrait™ GBS Assay as a standalone diagnostic tool, comparing its results directly against the reference culture method. The "algorithm" here refers to the automated PCR technology, sample preparation, and optical chip-based detection with integrated data analysis within the PA500 Portrait™ Analyzer System.

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

• The ground truth used was GBS culture testing (the "reference GBS clinical microbiology protocol"). This is a recognized laboratory gold standard for detecting GBS colonization.

8. The sample size for the training set:

• The document does not specify a separate training set sample size. The analytical studies describe various experiments (LoD, inclusivity, exclusivity, interference, carry-over, reproducibility) that might contribute to the development and refinement of the assay and its software, but these are not explicitly labeled as a "training set" in the context of machine learning, which is not the primary mechanism of this device. For an IVD like this, validation often involves demonstrating performance across various analytical and clinical scenarios rather than "training" an AI model.

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

• As no explicit "training set" for an AI model is described, the mention of ground truth establishment for such a set is not applicable. For the analytical studies, the ground truth for spiked samples was known by design (e.g., specific GBS strains at known concentrations, or known interfering substances).

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