(103 days)
Simplexa C. difficile Direct: The Focus Diagnostics Simplexa™ C. difficile Direct assay is intended for use on the Integrated Cycler instrument for the detection of Clostridium difficile toxin B gene (tcdB) present in liquid or unformed stool samples from individuals suspected of C. difficile infection (CDI). This test aids in the diagnosis of illness resulting from CDI. The assay is for professional and prescription use only.
Simplexa C. difficile Positive Control Pack: The Simplexa™ C. difficile Positive Control Pack is intended to be used as a control with the Simplexa™ C. difficile Direct kit. This control is not intended for use with other assays or systems.
The Simplexa™ C. difficile Direct assay system is a real-time PCR system that enables the direct amplification and detection of toxigenic C. difficile DNA from unprocessed liquid or unformed stool specimens that have not undergone nucleic acid extraction. The system consists of the Simplexa™ C. difficile Direct assay, the Integrated Cycler (with Integrated Cycler Studio Software), the Direct Amplification Disc and associated accessories. In the Simplexa™ C. difficile Direct assay, bi-functional fluorescent probe-primers are used together with corresponding reverse primers to amplify C. difficile and DNA internal control targets. The assay targets a sequence which is in a well conserved region of C. difficile toxin B gene (todB). A DNA internal control is used to detect PCR failure and/or inhibition
Acceptance Criteria and Device Performance for Simplexa C. difficile Direct
1. Table of Acceptance Criteria and Reported Device Performance
The provided document describes the performance of the Simplexa C. difficile Direct assay in comparison to various gold standards and other NAATs. The acceptance criteria are implicit in the presented tables.
Acceptance Criteria for Simplexa C. difficile Direct (versus Combined Culture + Toxin Assay):
| Metric | Acceptance Criteria (Implied) | Reported Device Performance | 95% Confidence Interval (CI) |
|---|---|---|---|
| Sensitivity | Not explicitly stated | 85.9% (336/391) | 82.1% to 89.0% |
| Specificity | Not explicitly stated | 95.1% (1849/1945) | 94.0% to 95.9% |
| PPV | Not explicitly stated | 77.8% (336/432) | 73.6% to 81.4% |
| NPV | Not explicitly stated | 97.1% (1849/1904) | 96.3% to 97.8% |
Additional Performance (versus other FDA-cleared NAATs for reference):
| Comparison | Metric | Reported Device Performance | 95% Confidence Interval (CI) |
|---|---|---|---|
| Simplexa vs NAAT-1 | Positive Agreement | 93.4% (114/122) | 87.6% to 96.6% |
| Negative Agreement | 96.6% (683/707) | 95.0% to 97.7% | |
| Simplexa vs NAAT-2 | Positive Agreement | 93.9% (138/147) | 88.8% to 96.7% |
| Negative Agreement | 94.0% (591/629) | 91.8% to 95.6% | |
| Simplexa vs NAAT-3 | Positive Agreement | 84.8% (112/132) | 77.8% to 90.0% |
| Negative Agreement | 99.2% (584/589) | 98.0% to 99.6% |
2. Sample Size Used for the Test Set and Data Provenance
The primary clinical performance study (method comparison) used 2351 samples prospectively collected.
- Data Provenance: Samples were prospectively collected from five (5) geographically diverse sites in the USA between December 3, 2015, and June 10, 2016.
- Evaluable Samples: 2330 samples were evaluable on Simplexa C. difficile Direct & the Direct Culture method, and 2336 were evaluable on Simplexa C. difficile Direct & the Combination of Direct/Enriched Culture methods.
- Invalid Rate: The initial invalid rate was 0.64% (15/2351), reduced to a final invalid rate of 0.13% (3/2351) after repeat testing.
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 for the clinical sample test set. However, the ground truth was based on Direct Culture + Toxin Assay and Combined Culture (Direct & Enriched) + Toxin Assay, with confirmatory testing using FDA cleared nucleic acid amplification test (NAAT) results for discrepant analysis. This implies that the ground truth was established by laboratory methods and not by individual expert interpretation.
4. Adjudication Method for the Test Set
For discrepant samples in the clinical study, discrepant analysis was performed using FDA cleared nucleic acid amplification test (NAAT) results provided by the sites.
- For the "Simplexa C. difficile Direct versus Direct Toxigenic Culture Method" table:
- 116/163 discrepant Simplexa-positive/Culture-negative samples were positive, and 46/163 were indeterminate for C. difficile Toxin B gene DNA when tested using an FDA cleared molecular test.
- 8/12 discrepant Simplexa-negative/Culture-positive samples were negative, and 4/12 were positive for C. difficile Toxin B gene DNA when tested using an FDA cleared molecular test.
- For the "Simplexa C. difficile Direct versus Combined Direct and Enriched Toxigenic Culture Methods" table:
- 59/96 discrepant Simplexa-positive/Culture-negative samples were positive, and 37/96 were negative for C. difficile Toxin B gene DNA when tested using an FDA cleared molecular test.
- 43/55 discrepant Simplexa-negative/Culture-positive samples were negative for C. difficile Toxin B gene DNA when tested using an FDA cleared molecular test.
This indicates an adjudication process involving a third, independent, FDA-cleared NAAT for resolving discrepancies between the investigational device and the culture methods.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done
No, an MRMC comparative effectiveness study was not explicitly described in the provided text. The study focuses on the performance of the analytical device rather than human reader interpretation with or without AI assistance.
6. If a Standalone Study (Algorithm Only Without Human-in-the-loop Performance) Was Done
Yes, the studies presented are standalone performance evaluations of the Simplexa C. difficile Direct assay. The assay is an automated real-time PCR system designed for direct detection of C. difficile toxin B gene, meaning its performance is measured independently of human interpretation of its results, although trained lab personnel would operate the instrument.
7. The Type of Ground Truth Used
The ground truth for the clinical performance study was established using:
- Direct Culture + Toxin Assay
- Combined Culture (Direct & Enriched) + Toxin Assay
- FDA cleared molecular tests (NAATs) for discrepant analysis.
This represents a composite reference standard based on microbiological culture techniques and molecular detection for toxigenic C. difficile, with additional molecular confirmation for discordant results.
8. The Sample Size for the Training Set
The document does not specify a separate "training set" sample size. The studies described are performance evaluations of the device, implying that the device's development and internal optimization would have occurred prior to these validation studies. Therefore, information regarding a training set is not provided as this is a diagnostic assay, not a machine learning algorithm that requires a separate training and test set in the same way.
9. How the Ground Truth for the Training Set Was Established
As no specific training set is mentioned for the device (which is a molecular diagnostic assay), the method for establishing ground truth for such a set is not applicable or described in this document. The focus is on the analytical and clinical validation of the completed product.
§ 866.3130 Clostridium difficile toxin gene amplification assay.
(a)
Identification. AClostridium difficile toxin gene amplification assay is a device that consists of reagents for the amplification and detection of target sequences inClostridium difficile toxin genes in fecal specimens from patients suspected of havingClostridium difficile infection (CDI). The detection of clostridial toxin genes, in conjunction with other laboratory tests, aids in the clinical laboratory diagnosis of CDI caused byClostridium difficile. (b)
Classification. Class II (special controls). The special controls are set forth in FDA's guideline document entitled: “Class II Special Controls Guideline: Toxin Gene Amplification Assays for the Detection ofClostridium difficile; Guideline for Industry and Food and Drug Administration Staff.” See § 866.1(e) for information on obtaining this document.