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The Accula™ Strep A Test performed on the Accula Dock is a molecular in vitro diagnostic test utilizing polymerase chain reaction (PCR) and lateral flow technologies for the qualitative, visual detection of Streptococcus pyogenes (Group A B-hemolytic Streptococcus, Strep A) bacterial nucleic acid. It is intended to aid in the rapid diagnosis of Group A Streptococcus bacterial infections from throat swabs of patients with signs and symptoms of pharyngitis.

All negative test results should be confirmed by bacterial culture because negative results do not preclude infection with Group A Streptococcus and should not be used as the sole basis for treatment.

The Accula™ Strep A Test is a semi-automated, colorimetric polymerase chain reaction (PCR) nucleic acid amplification test to qualitatively detect Streptococcus pyogenes (Group A Bhemolytic Streptococcus, Strep A) bacterial nucleic acid from unprocessed throat swabs that have not undergone prior nucleic acid extraction. The system integrates nucleic acid extraction, a novel Mesa Biotech PCR nucleic acid amplification technology named OscAR™, and hybridization-based visual detection into a completely self-contained and automated system. The Accula Strep A system consists of a small reusable Dock to drive the automated testing process, and a single-use disposable test cassette that contains all the enzymes and reagents.

The Mesa Biotech Accula Strep A Test is an in vitro diagnostic test for the qualitative, visual detection of Streptococcus pyogenes (Group A B-hemolytic Streptococcus, Strep A) bacterial nucleic acid from throat swabs. The device integrates nucleic acid extraction, OscAR™ PCR amplification technology, and hybridization-based visual detection.

Acceptance Criteria and Device Performance:

The primary performance metrics for the Accula Strep A Test were Sensitivity, Specificity, Positive Percent Agreement (PPA), and Negative Percent Agreement (NPA). These were evaluated against a reference bacterial culture and an FDA-cleared molecular comparator.

Study Details:

1. Sample Size and Data Provenance:

   • Test Set (Clinical Study):
     • Evaluable for Accula vs. Culture: 654 samples from 669 enrolled subjects.
     • Evaluable for Accula vs. Molecular Comparator: 648 samples from 669 enrolled subjects.
     • Provenance: Prospective clinical study conducted at nine U.S. sites from May 2019 to January 2020.
   • Reproducibility/Near-Cutoff Study: 90 samples per condition (Low Positive, Moderate Positive, Negative) tested across three CLIA-waived sites. These were contrived throat swabs.
   • Limit of Detection (LoD): Replicates of 20 for confirmatory testing of two Strep A strains.
   • Analytical Reactivity: 3 replicates per strain (4 strains total) at two concentrations.
   • Analytical Specificity (Cross-Reactivity): 3 replicates per organism (47 organisms total), both in presence and absence of Strep A.
   • Interfering Substances: 3 replicates per substance, positive and negative Strep A samples.

2. Number of Experts and Qualifications for Test Set Ground Truth:

   • The document does not explicitly state the "number of experts" used to establish the ground truth for the clinical test set. However, for the reference methods:
     • Bacterial Culture (Blood Agar Culture): Performed at a "central laboratory" according to "instructions from the reference laboratory." This implies trained laboratory personnel, but specific qualifications are not detailed.
     • FDA-cleared molecular test (comparator): Performed at the central laboratory.
     • Second FDA-cleared molecular test (discrepant analysis): Used for all discrepant results.

3. Adjudication Method for the Test Set:

   • For the clinical study, a discrepant analysis method was used. "All specimens generating discrepant results between the Accula Strep A Test and Blood Agar Culture, or between Accula and the molecular comparator test, were tested with a second FDA-cleared molecular test." This effectively acts as a "tie-breaker" or confirmatory method for unusual results.

4. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study:

   • No MRMC comparative effectiveness study was specifically described in terms of human readers' improvement with AI vs. without AI assistance.
   • However, the Reproducibility/Near-Cutoff Study and the CLIA Waiver Studies involved "non-laboratory personnel" at "CLIA-waived sites" (Point of Care sites) to demonstrate that the device could be accurately used by intended users in the intended environment. This indirectly assesses the effectiveness of the device in the hands of typical users, rather than an AI assistance to human readers.

5. Standalone (Algorithm Only) Performance:

   • Yes, the clinical performance described (Sensitivity, Specificity, PPA, NPA) represents the standalone performance of the Accula Strep A Test against established reference methods (Blood Agar Culture and FDA-cleared molecular tests). The device itself is a semi-automated system; these metrics evaluate its diagnostic accuracy independent of a human interpretation layer (beyond reading the visual result in the lateral flow).

6. Type of Ground Truth Used:

   • For the clinical study, the primary ground truth was bacterial culture (Blood Agar Culture) for Streptococcus pyogenes.
   • A second FDA-cleared molecular test was used as a confirmatory ground truth for discrepant results.
   • Additionally, an FDA-cleared molecular comparator method served as another reference standard for direct comparison.
   • For analytical studies (LoD, Reactivity, Specificity, Interfering Substances), the ground truth was established by contriving samples with known concentrations of specific organisms or substances.

7. Sample Size for the Training Set:

   • The document describes performance studies (validation). It does not provide information on a "training set" in the context of machine learning, as this is a nucleic acid amplification test, not an AI-driven image analysis or algorithm that would typically require a training set. The device's components (enzymes, reagents, PCR technology) are developed and optimized rather than "trained."

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

   • Not applicable as described in item 7. The device operates on molecular principles and does not involve a machine learning training phase with a labeled dataset in the traditional sense.

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