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Focus Diagnostics' Plexus™HerpeSelect®1 and 2 IgG is intended for qualitatively detecting the presence or absence of human IgG class antibodies to HSV-1 and HSV-2 in human sera. The test is indicated for testing sexually active adults or expectant mothers for aiding in the presumptive diagnosis of HSV-1 and HSV-2 infection. The predictive value of a positive or negative result depends on the population's prevalence and the pretest likelihood of HSV-1 and HSV-2 infection. The performance of this assay has not been established for use in a pediatric population, for neonatal screening, for testing of immunocompromised patients, for use by a point of care facility or for use with automated equipment.

The Focus Diagnostics Plexus™HerpeSelect®1 and 2 IgG is a multiplexed immunoassay for qualitatively detecting and differentiating human IgG antibodies to HSV-1 and HSV-2. The Focus Diagnosics Plexus™HerpeSelect®1 and 2 IgG uses an Antigen Bead suspension that contains two distinct HSV antigen bead types that fluoresce at different wavelengths and/or intensities: gG-1 beads. The Focus Diagnostics Plexus 100 HerpeSelect®1 and 2 IgG is a three step procedure. Patient sera are diluted, and the diluted sera are incubated with Antibodies are present, then the 1 . antibodies bind to the corresponding antigen beads. Phycoerythrin-conjugated goat anti-human IgG, (Conjugate) is added, and the Conjugate binds to the bound HSV 2. antibody (if present), and forms a Conjugate-HSV antibody-antigen bead sandwich. Fluorescence from each distinct HSV antigen bead type is measured and compared against a Cut-off Calibrator. 3.

Here's a breakdown of the acceptance criteria and study details for the Plexus HerpeSelect 1 and 2 IgG device, based on the provided document:

Acceptance Criteria and Device Performance

Note: The document does not explicitly state the pre-defined "acceptance criteria" as numerical thresholds beyond what is simply reported for the CDC panel. The "acceptance criteria" column above infers a reasonable expectation based on the device's intended use and the reported performance.

Study Details

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

   • Expectant Mothers: n=300 (150 from Focus Diagnostics, 150 from an external investigator at a University laboratory in Northern California). Sera were collected in the Pacific Northwestern United States. Retrospective (sequentially submitted, archived, and masked).
   • Sexually Active Adults: n=300 (150 from Focus Diagnostics, 150 from an external investigator at a clinical laboratory in Southern California). Sera were collected in the Pacific Northwestern United States. Retrospective (sequentially submitted, archived, and masked).
   • CDC HSV/CMV Panel: n=100 (contains duplicate samples of 50 test sera, effectively 50 unique sera for agreement, but 100 samples for reproducibility). Source: CDC.
   • Low Prevalence Population: n=77 (from Focus Diagnostics). Sera from patients aged 18 and 19 years, submitted to a clinical laboratory in Southern California from states with a history of low STD prevalence. Sera indicating immunocompromised status or previous herpesvirus testing were excluded. Retrospective (sequentially selected, archived, and masked).
   • Cross-reactivity: n=51 (37 "HSV ELISA dual negative" and 14 "HSV ELISA mixed sero-reactivity"). Source not explicitly stated, but likely laboratory archived samples tested by Focus.

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

   • The document implies that the Focus HerpeSelect 1 and 2 Immunoblot IgG was the reference method used to establish ground truth for the Expectant Mothers, Sexually Active Adults, and Low Prevalence Population studies. For the CDC panel, it states "CDC Result" as the ground truth.
   • The document does not specify the number of experts or their qualifications for interpreting the Immunoblot results or for establishing the CDC results.

3. Adjudication method for the test set:

   • The document does not explicitly state an adjudication method for ambiguous or discordant results between the reference method (Immunoblot/CDC Result) and the Plexus device. The data shows samples categorized as "Eqv" (equivocal) for the Plexus device, but no details on how these were handled in the agreement calculations or if an adjudication process was in place.

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 MRMC comparative effectiveness study was not done. This device is an in vitro diagnostic (IVD) assay, specifically a multiplexed immunoassay for detecting antibodies. It does not involve human readers interpreting images or data that an AI might assist with. Therefore, the concept of "human readers improve with AI vs without AI assistance" is not applicable.

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

   • Yes, this is effectively a standalone performance study. The device itself is an automated assay that produces a qualitative result (positive, negative, or equivocal) for HSV-1 and HSV-2 IgG antibodies. Its performance is evaluated against a reference standard without human interpretation being a variable in the device's output.

6. The type of ground truth used:

   • Serological Reference Method / Consensus Standard:
     • For Expectant Mothers, Sexually Active Adults, and Low Prevalence Population studies, the Focus HerpeSelect 1 and 2 Immunoblot IgG was used as the reference method. This is a commonly accepted confirmatory test for HSV serology.
     • For the CDC panel, the "CDC Result" served as the ground truth, implying a characterized and validated reference panel.

7. The sample size for the training set:

   • The document does not specify distinct "training set" sizes. For IVD assays like this, the development process usually involves internal validation and optimization, but a formal "training set" like in machine learning algorithms is not typically detailed or distinguished in regulatory summaries. The studies described are primarily for performance validation.

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

   • As no specific "training set" is detailed, the method for establishing ground truth for any internal development or optimization (which would be analogous to training) is not provided. However, it can be inferred that similar validated reference methods (like Immunoblot or well-characterized panels) would have been used during the development phase.

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