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The Focus Technologies West Nile Virus ELISA IgG is intended for qualitatively detecting IgG antibodies to West Nile virus in human serum. In conjunction with the Focus Technologies West Nile Virus IgM Capture ELISA, the test is indicated for testing persons having symptoms of meningioencephalitis, as an aid in the presumptive laboratory diagnosis of West Nile virus infection. Positive results must be confirmed by neutralization test, or by using the current CDC guidelines for diagnosing West Nile encephalitis. This test is not intended for self-testing, and this test is not FDA cleared nor approved for testing blood or plasma donors. Assay performance characteristics have not been established for automated instruments.

Indirect Enzyme-linked immunosorbent assay for qualitatively detecting human serum IgG antibodies to West Nile virus.

Here's a detailed breakdown of the acceptance criteria and the study that proves the Focus Technologies West Nile Virus ELISA IgG device meets them, based on the provided text:

Acceptance Criteria and Device Performance for Focus Technologies West Nile Virus ELISA IgG

The document does not explicitly state pre-defined acceptance criteria (e.g., "sensitivity must be > X%") for the device. Instead, it reports the device's performance characteristics from various studies. Therefore, the "acceptance criteria" presented below are inferred from the reported performance, implying that these levels of performance were deemed acceptable for market clearance.

1. Table of Acceptance Criteria (Inferred) and Reported Device Performance

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

• Study Site 1 (Encephalitis/Meningitis Patients):
  • Sample Size: 300 total patients (37 confirmed positive, 210 presumptive results, 53 unclassified). Performance calculated on 242 samples (37 confirmed positive + 205 presumptive negative).
  • Data Provenance: Sera were sequentially submitted to a state department of health laboratory in the northeastern U.S., archived, and masked. Retrospective.
• Study Site 2 (WNV PRNT Positives):
  • Sample Size: 75 retrospective sera.
  • Data Provenance: Sera were sequentially submitted to a clinical laboratory in the mid-western U.S., archived. Retrospective.
• Study Site 3 (WNV IFA Negatives):
  • Sample Size: 157 samples.
  • Data Provenance: Retrospective sera from a clinical laboratory in the southwestern U.S.
• Study Site 4 (Suspected Encephalitis/Meningitis Patients):
  • Sample Size: 50 sera (1 confirmed positive, 49 presumptively negative).
  • Data Provenance: Retrospective and masked sera provided by a U.S. federal government laboratory.
• Study Site 4 (Non-Flavivirus Test Samples):
  • Sample Size: 476 samples. Performance calculated on 461 samples (21 CDC ELISA positive + 440 CDC ELISA negative).
  • Data Provenance: Prospectively collected from North America (August 2003) and submitted to a clinical laboratory in Southern California for non-flavivirus tests. Prospective, but the "test set" for WNV performance was created using the CDC ELISA.
• Cross-reactivity Studies:
  • Sample Size: 75 sera (20 Dengue, 20 Japanese encephalitis, 21 St. Louis encephalitis, 20 Yellow fever, 17 Alphavirus, 15 Bunyavirus, 60 HSV-1, 12 EBV, 20 Cytomegalovirus, 20 Echovirus/Poliovirus, 20 Lyme disease).
  • Data Provenance: Sera were archived and masked, conducted at Focus (Study Site 4, for most pathogens) and a state department of health laboratory in the northeastern U.S. (DOH, for SLE positives). Retrospective.
• Freeze-Thaw Study:
  • Sample Size: 8 sera (5 positive, 3 negative).
  • Data Provenance: Conducted at Focus (Study Site 4).
• Reproducibility Studies:
  • Sample Size: Inter-lot: 5 samples; Inter/Intra-assay: 7 samples; Inter-laboratory: 7 samples.
  • Data Provenance: Conducted at Focus (Study Site 4), a state department of health laboratory in the northeastern U.S. (Study Site 1), and a clinical laboratory in the mid-western U.S. (Study Site 2).

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

The document does not explicitly state the "number of experts" or their "qualifications" involved in establishing the ground truth. However, it indicates:

• Reference Methods Used:
  • CDC West Nile Virus IgG Capture ELISA
  • Plaque Reduction Neutralization Test (PRNT) for West Nile virus
  • Dengue PRNT
  • St. Louis Encephalitis (SLE) PRNT
  • West Nile Virus native antigen ELISA
  • West Nile IFA

These are established laboratory assays, and their results are considered the "ground truth." The implication is that skilled laboratory personnel at the respective state, federal, and clinical laboratories performed these reference tests. The qualifications of these individuals (e.g., highly trained lab technologists, clinical microbiologists) are inherent to the operation of such labs but are not specified in terms of "years of experience" or "radiologist" equivalent, as this is an in vitro diagnostic device.

4. Adjudication Method for the Test Set

The document does not describe an explicit "adjudication method" in the sense of multiple experts independently evaluating cases and resolving discrepancies (e.g., 2+1, 3+1).

Instead, the "ground truth" was established by reference laboratory assays (CDC WNV IgG ELISA, PRNT, IFA), which inherently have their own established protocols for result interpretation. For example, "confirmed positive West Nile encephalitis patients" were defined by symptoms and positive results from both CDC WNV IgG ELISA and WNV PRNT. Equivocal or indeterminant results from reference assays were often excluded from performance calculations.

5. If a Multi Reader Multi Case (MRMC) Comparative Effectiveness Study Was Done

No, a Multi Reader Multi Case (MRMC) comparative effectiveness study was not done. This type of study typically involves comparing human reader performance with and without an AI-assisted device in diagnostic imaging contexts. The Focus Technologies West Nile Virus ELISA IgG is an in vitro diagnostic laboratory test, not an imaging device intended for human interpretation.

6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done

Yes, the studies conducted evaluated the standalone performance of the Focus Technologies West Nile Virus ELISA IgG device (an algorithm/assay only). The device itself is an indirect ELISA designed to qualitatively detect antibodies, implying that the interpretation of the optical density readings and the final result (positive, negative, equivocal) is performed by the device's internal algorithms or by comparison to defined cut-offs, without a "human-in-the-loop" decision support role in the sense of AI for image interpretation. The performance metrics presented (sensitivity, specificity/agreement) directly reflect the device's ability to classify samples based on its own output against established reference methods.

7. The Type of Ground Truth Used

The primary types of ground truth used were:

• Reference Laboratory Assay Results:
  • CDC West Nile Virus IgG Capture ELISA: A highly respected and commonly used reference method for WNV IgG.
  • Plaque Reduction Neutralization Test (PRNT): Considered the gold standard for serological confirmation of arbovirus infections due to its high specificity.
  • West Nile IFA (Immunofluorescence Assay): Another serological test.
  • Dengue PRNT, SLE PRNT: Used for cross-reactivity assessment.
  • West Nile virus native antigen ELISA: Used as a screening method in Study Site 2 before PRNT confirmation.
• Clinical Criteria: For Study Site 1 and 4, patient presentation (meningioencephalitis symptoms, fever, altered mental status, CSF findings) was combined with laboratory results to define confirmed cases.

This combination of highly specific and sensitive reference assays, often coupled with relevant clinical symptoms, provides a robust ground truth for an in vitro diagnostic device.

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 development. This device is an ELISA, which is typically a biochemically-based assay, not an AI/ML algorithm that requires a separate training phase with labeled data in the same way. The performance studies evaluate the assay's built characteristics against clinical samples and reference methods.

If one were to loosely interpret "training" as the internal development and calibration of the assay (e.g., setting cut-offs), the size of the samples used for that purpose is not detailed. The provided studies are primarily for performance validation.

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

As noted above, there isn't a "training set" in the AI/ML sense for this ELISA device. The concept of "ground truth" for the internal development and establishment of assay cut-offs would typically involve:

• Well-characterized panels: Samples from individuals with known WNV infection status (confirmed by PRNT or PCR) and known negative individuals.
• Titration and statistical analysis: To determine optimal cut-off values for distinguishing positive, negative, and equivocal results based on optical density readings.

However, the document focuses on the validation studies performed to demonstrate the device's performance against established reference methods and clinical populations, rather than detailing its initial development and calibration.

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