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The DiaSorin Molecular Simplexa™ VZV Swab Direct assay is intended for use on the LIAJSON® MDX instrument for the qualitative detection of varicella-zoster virus (VZV) DNA present in cutaneous and mucocutaneous lesion swabs from patients with signs and symptoms of VZV infection. This test is intended as an aid in the diagnosis of VZV infection. Negative results do not preclude VZV infection and should not be used as the sole basis for treatment or other patient management decisions.

The Simplexa™ VZV Positive Control Pack is intended to be used as a control with the Simplexa™ VZV Direct kit and the Simplexa™ VZV Swab Direct kit on the LIAISON® MDX Instrument. It is not intended for use with other assays or systems.

The Simplexa™ VZV Swab Direct assay is a real-time PCR system that enables the direct amplification and detection of VZV DNA from unprocessed cutaneous and mucocutaneous lesion swab specimens without nucleic acid extraction. The system consists of the Simplexa™ VZV Swab Direct assay, the LIAISON® MDX (with LIAISON® MDX Studio Software), the Direct Amplification Disc (DAD) and associated accessories.

In the Simplexa™ VZV Swab Direct assay, fluorescent probes are used together with corresponding forward and reverse primers to amplify VZV and internal control targets. A well-conserved region of the VZV DNA polymerase gene is targeted to identify VZV DNA in the specimen. An internal control is used to detect PCR failure and/or inhibition.

This document describes the validation of the DiaSorin Molecular Simplexa™ VZV Swab Direct assay. The assay is intended for the qualitative detection of varicella-zoster virus (VZV) DNA directly from cutaneous and mucocutaneous lesion swabs.

1. Table of Acceptance Criteria and Reported Device Performance:

The document implicitly defines acceptance criteria through the results of the clinical and analytical studies, which consistently demonstrate high agreement and sensitivity/specificity.

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

• Prospective Study: 452 cutaneous and mucocutaneous specimens.
  • Data Provenance: Collected from 10 collection sites across the USA (November 2018 - May 2019). This is prospective data.
• Retrospective Study: 60 positive and 120 negative (masked) cutaneous and mucocutaneous swab specimens. Total of 180 samples.
  • Data Provenance: Retrospective and blinded, specific country not mentioned but implied to be related to DiaSorin Molecular (Cypress, California, USA).
• Contrived Sample Study: 60 contrived positive specimens (30 VZV Ellen, 30 VZV 9939) and 60 masked negative specimens. Total of 120 samples.
  • Data Provenance: Contrived samples are laboratory-prepared.

3. 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 specific "qualifications" (e.g., "radiologist with 10 years of experience") for establishing the ground truth. Instead, it describes a "Composite Reference Method (CRM)" for the prospective study and "Composite Reference Method 2 (CRM 2)" for the retrospective and contrived studies.

• Prospective Study (CRM): The ground truth involved a three-part composite reference method:
  1. VZV direct stain fluorescent antibody (DSFA) and/or culture isolation with direct fluorescent antibody (DFA) performed by one testing site.
  2. Two validated VZV polymerase chain reaction (PCR) assays followed by bi-directional sequencing performed by another testing site.
• Retrospective and Contrived Studies (CRM 2): The ground truth utilized a two out of three outcome from:
  1. One FDA Cleared NAAT PCR assay for VZV (performed by one external site).
  2. Two validated VZV PCR assays followed by bi-directional sequencing (performed by different DiaSorin Molecular operators).

While these methods represent established laboratory diagnostic techniques, the specific number and qualifications of individuals performing or interpreting these reference methods are not detailed.

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

• Prospective Study: The document doesn't explicitly state an adjudication method like "2+1" or "3+1." It mentions a "three (3) part composite reference method." The results presented ("sensitivity" and "specificity") suggest a consensus or majority rule type of adjudication where the CRM's outcome defines the true positive/negative.
• Retrospective and Contrived Studies: The ground truth (CRM 2) explicitly used a "two (2) out of three (3) outcome" from the reference methods, which is a form of majority rule adjudication.

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 is a diagnostic device (molecular assay) for the detection of VZV DNA, not an AI-powered image analysis tool for human readers. Therefore, a multi-reader multi-case (MRMC) comparative effectiveness study with human readers (or improvement with AI assistance) is not applicable and was not performed. The device itself is a standalone diagnostic test performed by laboratory personnel.

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

Yes, the studies described are standalone performance studies of the Simplexa™ VZV Swab Direct assay. The assay is an in vitro diagnostic test that provides a qualitative result (positive or negative for VZV DNA) based on real-time PCR, effectively operating as an "algorithm only" in the sense that its output is directly read without requiring further human interpretive modifications beyond standard laboratory operating procedures.

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

The ground truth used was a composite reference method consisting of:

• For the Prospective Study:
  • VZV direct stain fluorescent antibody (DSFA) and/or culture isolation with direct fluorescent antibody (DFA).
  • Two validated VZV polymerase chain reaction (PCR) assays followed by bi-directional sequencing.
• For the Retrospective and Contrived Studies:
  • One FDA Cleared NAAT PCR assay for VZV.
  • Two validated VZV PCR assays followed by bi-directional sequencing.

This combination indicates a sophisticated, multi-modal ground truth incorporating both direct viral detection/culture and highly sensitive molecular methods with genetic confirmation (sequencing). This is a robust form of ground truth for pathogen detection.

8. The sample size for the training set:

The document does not describe a "training set" in the context of machine learning. The studies described are validation studies for a molecular diagnostic assay. The assay's design (primers, probes, reaction conditions) would have been developed/optimized prior to these validation studies, but this process is not typically referred to as "training" in the same way as for AI/ML models.

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

As there is no "training set" in the AI/ML sense, this question is not applicable. The ground truth for the validation (test) sets was established using the Composite Reference Methods described in point 7.

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