(144 days)
The SHIGA TOXIN CHEK test is an enzyme immunoassay for the simultaneous qualitative detection of Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2) in a single test. It is intended for use with human fecal samples from patients with gastrointestinal symptoms to aid in the diagnosis of disease caused by Shiga Toxin producing Escherichia coli (STEC). It may be used directly with human fecal specimens, or broth or plate cultures derived from fecal specimens. The test results should be considered in conjunction with the patient history. FOR IN VITRO DIAGNOSTIC USE.
The SHIGA TOXIN CHEK test uses antibodies to Stx1 and Stx2. The microassay wells supplied with the kit contain immobilized monoclonal antibodies against Stx1 and Stx2. The detecting antibody consists of a mixture of anti-Stx1 and anti-Stx2 polyclonal antibodies conjugated to horseradish peroxidase. In the assay, an aliquot of a fecal specimen or culture is emulsified in the Diluent and the diluted specimen is then transferred to the microassay well containing the detecting antibody. If Stx1 and/or Stx2 are present in the specimen, they will bind to the detecting antibody and to the immobilized monoclonal antibodies during the incubation phase. Any unbound material is removed during the washing steps. Following the addition of substrate, a color is detected due to the enzyme-antibody-antigen complexes that form in the presence of toxin.
The SHIGA TOXIN CHEK test is an enzyme immunoassay for the simultaneous qualitative detection of Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2). It is intended for use with human fecal samples from patients with gastrointestinal symptoms to aid in the diagnosis of disease caused by Shiga Toxin producing Escherichia coli (STEC).
Here's the breakdown of acceptance criteria and the study results:
1. Table of Acceptance Criteria and Reported Device Performance
| Performance Metric | Acceptance Criteria (Implicit) | Reported Device Performance (Direct Fecal Testing) | Reported Device Performance (Broth Cultures) |
|---|---|---|---|
| Sensitivity | High (e.g., >95%) | 100% | 97.1% |
| Specificity | High (e.g., >95%) | 99.9% | 99.7% |
| Correlation | High (e.g., >95%) | 99.9% | 99.5% |
| Reproducibility | 100% agreement | 100% agreement | Not explicitly stated for broth cultures (but for overall test) |
| Analytical Sensitivity (LOD) for Stx1 (direct fecal) | Should detect low concentrations | 0.28 ng/mL | N/A |
| Analytical Sensitivity (LOD) for Stx2 (direct fecal) | Should detect low concentrations | 0.23 ng/mL | N/A |
| Analytical Sensitivity (LOD) for Stx1 (broth cultures) | Should detect low concentrations | N/A | 0.18 ng/mL |
| Analytical Sensitivity (LOD) for Stx2 (broth cultures) | Should detect low concentrations | N/A | 0.30 ng/mL |
| Analytical Specificity (Cross-Reactivity) | No interference from common bacterial/viral strains | No interference | No interference |
| Precision - Intra-Assay | Positive remain positive, negative remain negative | 100% (positives remained positive, negatives remained negative) | Not explicitly stated for broth cultures (but for overall test) |
| Precision - Inter-Assay | Positive remain positive, negative remain negative | 100% (positives remained positive, negatives remained negative) | Not explicitly stated for broth cultures (but for overall test) |
2. Sample Size Used for the Test Set and Data Provenance
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Clinical Performance - Direct Fecal Testing:
- Sample Size: 913 samples (899 fresh and 14 frozen specimens).
- Data Provenance: Not explicitly stated, but clinical performance was evaluated at 3 independent sites, suggesting a mix of retrospective and prospective clinical samples. The origin country is not specified.
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Clinical Performance - Broth Cultures:
- Sample Size: 789 samples.
- Data Provenance: Not explicitly stated, but clinical performance was evaluated at 3 independent sites, suggesting a mix of retrospective and prospective clinical samples. The origin country is not specified.
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Reproducibility:
- Sample Size: 11 fecal specimens (coded to prevent identification).
- Data Provenance: Tested at 2 independent laboratories and on-site at TECHLAB®, Inc.
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Analytical Sensitivity (LOD):
- Sample Size: Replicates of 20 for each toxin dilution in a negative fecal pool (direct fecal) or overnight GN broth culture (broth cultures).
- Data Provenance: Laboratory controlled experiments using highly purified Stx1 and Stx2.
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Analytical Specificity (Cross Reactivity):
- Sample Size: A panel of various bacterial and viral strains.
- Data Provenance: Laboratory controlled experiments.
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Precision - Intra-Assay:
- Sample Size: 6 positive fecal specimens and 6 negative fecal specimens, each assayed in replicates of eight.
- Data Provenance: Laboratory controlled experiments.
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Precision - Inter-Assay:
- Sample Size: 12 fecal specimens (six negative, two positive for Stx1, two positive for Stx2, and two positive for both Stx1 and Stx2).
- Data Provenance: Laboratory controlled experiments.
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts
The ground truth for the clinical performance studies (Direct Fecal Testing and Broth Cultures) was established using the Vero Cell Cytotoxin Assay with neutralization. This is referred to as the "Clinical Reference Standard (Gold Standard)" in the document.
- Number of Experts: Not specified. The Vero Cell Cytotoxin Assay is a laboratory-based method, and its interpretation would typically be performed by trained laboratory personnel.
- Qualifications of Experts: Not specified. It's implied that trained microbiologists or laboratory technicians would perform and interpret the gold standard assay.
4. Adjudication Method for the Test Set
The document does not explicitly describe an adjudication method for discrepancies between the SHIGA TOXIN CHEK test and the Vero Cell Cytotoxin Assay. The results provided are direct comparisons. For example, in the direct fecal testing, 78 samples were positive by both methods, 1 was positive by SHIGA TOXIN CHEK and negative by the cytotoxin assay, and 0 were negative by SHIGA TOXIN CHEK and positive by the cytotoxin assay. This suggests that the cytotoxin assay was considered the definitive ground truth, and no further adjudication process is mentioned for conflicting results.
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 information is not applicable to the SHIGA TOXIN CHEK device. This is an enzyme immunoassay for detecting toxins, not an imaging or diagnostic device that involves human "readers" in the context of interpretation that could be assisted by AI. The device directly produces a qualitative (positive/negative) result based on an enzymatic reaction and color change.
6. If a Standalone (i.e. algorithm only without human-in-the-loop performance) was done
The SHIGA TOXIN CHEK is a standalone device in that its performance metrics (sensitivity, specificity, correlation) are reported directly against the gold standard (Vero Cell Cytotoxin Assay) without a human interpretation step that would then be assisted by the device. The device itself performs the detection. The results are read based on a colorimetric reaction, which is then interpreted as positive or negative. The "study" (clinical performance) focuses on the device's accuracy in identifying the presence of the toxins compared to the established gold standard.
7. The Type of Ground Truth Used
The primary ground truth used for the clinical performance studies was the Vero Cell Cytotoxin Assay with neutralization, described as the "Clinical Reference Standard (Gold Standard)".
- For analytical studies (LOD, cross-reactivity, precision), the ground truth was established through controlled laboratory experiments using known concentrations of purified toxins or specific bacterial/viral strains.
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 models. This device is an immunoassay, and its development would typically involve optimization and validation rather than a distinct "training set" for an algorithm. The clinical and analytical studies serve as validation of the device's performance.
9. How the Ground Truth for the Training Set Was Established
As there is no explicit "training set" described in the context of an AI/ML model for this immunoassay, this question is not applicable. The ground truth for the validation (test) sets was established using the Vero Cell Cytotoxin Assay with neutralization.
§ 866.3255
Escherichia coli serological reagents.(a)
Identification. Escherichia coli serological reagents are devices that consist of antigens and antisera used in serological tests to identifyEscherichia coli from cultured isolates derived from clinical specimens. Additionally, some of these reagents consist ofEscherichia coli antisera conjugated with a fluorescent dye used to identifyEscherichia coli directly from clinical specimens or cultured isolates derived from clinical specimens. The identification aids in the diagnosis of diseases caused by this bacterium belonging to the genusEscherichia, and provides epidemiological information on diseases caused by this microorganism. AlthoughEscherichia coli constitutes the greater part of the microorganisms found in the intestinal tract in humans and is usually nonpathogenic, those strains which are pathogenic may cause urinary tract infections or epidemic diarrheal disease, especially in children.(b)
Classification. Class I (general controls). The device is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to the limitations in § 866.9.