(87 days)
The Xpert® C. difficile/Epi test is a qualitative in vitro diagnostic test for detection of toxin B gene sequences and for presumptive identification of 027/NAP1/BI strains of toxigenic Clostridioides difficile from unformed (liquid or soft) stool specimens collected from patients suspected of having C. difficile infection (CDI). Presumptive identification of 027/NAP1/BI strains of C. difficile is by detection of binary toxin (CDT) gene sequences and the single base pair deletion at nucleotide 117 in the tcdC gene. The tcdC gene encodes for a negative regulator in C. difficile toxin production. The test is performed on the GeneXpert® Instrument Systems and utilizes automated real-time polymerase chain reaction (PCR) to detect toxin gene sequences associated with toxin producing C. difficile. The Xpert® C. difficile/Epi test is intended as an aid in the diagnosis of CDI. Detection of 027/NAP/Bl strains of C. difficile by the Xpert® C. difficile/Evi test is presumptive and is solely for enidemiological purposes and is not intended to guide or monitor treatment for C. difficile infections. Concomitant culture is necessary only if further typing or organism recovery is required.
The Xpert C. difficile/Epi test is an automated in vitro diagnostic test for qualitative detection of toxin producing Clostridioides difficile (formerly known as Clostridium difficile) directly from unformed (liquid or soft) stool specimens of patients suspected of having Clostridioides difficile infection (CDI). The test detects the toxin B gene (tcdB), the binary toxin (CDT) gene, and the single base pair deletion at nucleotide 117 (tcdCΔ117) within the gene encoding TcdC, a negative regulator of toxin production. The combined presence of the genes encoding toxin B and binary toxin and the tcdCA117 deletion has been associated with a hypervirulent C. difficile strain known as 027/NAP1/BI, which has been associated with severe disease outbreaks in healthcare facilities worldwide.
The test is performed on the GeneXpert® Instrument Systems (comprised of the GeneXpert® Dx System. GeneXpert® System with Touchscreen, and GeneXpert® Infinity System). In the GeneXpert® Instrument Systems, sample preparation, amplification, and real-time detection are all fully automated and completely integrated. The single-use disposable Xpert C. difficile/Evi cartridge, required by the platform for use, holds the PCR reagents and hosts the PCR process. Because the cartridge is self-contained, cross-contamination between samples is minimized.
The Xpert C. difficile/Epi test includes reagents for the detection of toxigenic C. difficile and the detection of sequences for presumptive identification of 027/NAP 1/BI strains. In addition, the test reagents include an internal sample processing control (SPC) to ensure adequate processing of the target bacteria and to monitor the presence of inhibitor(s) in the PCR Assay. The SPC also ensures that the PCR conditions (temperature and time) are appropriate for the amplification reaction and that the PCR reagents are functional. The Probe Check Control (PCC) verifies reagent rehydration, PCR tube filling in the cartridge, probe integrity, and dye stability.
The Xpert C. difficile/Evi test system performs sample preparation and real-time, multiplex polymerase chain reaction (PCR) for detection of target-specific DNA. A swab is inserted into the stool specimen and then placed in a tube containing Sample Reagent. Following brief vortexing, the content of the Sample Reagent is transferred to the Sample Chamber of the disposable fluidic cartridge (the Xpert C. difficile/Epi cartridge). The user initiates a test from the system user interface of the GeneXpert® Instrument Systems and places the cartridge with sample into a GeneXpert® instrument system which performs hands-off real-time PCR for detection of C. difficile DNA.
Depending on the specific instrument, a GeneXpert® instrument system may contain 1-80 modules, each of which are randomly accessible and capable of performing separate sample preparation and real-time PCR tests for the detection of gene sequences for C. difficile toxin B and binary toxin and the tcdCA117 deletion in less than 45 minutes. Each module contains a syringe drive for dispensing fluids (i.e., the syringe drive activates the plunger that works in concert with the rotary valve in the cartridge to move fluids between chambers), an ultrasonic horn for lysing cells or spores, and a proprietary I-CORE® thermocycler for performing real-time PCR and detection.
Each instrument in the GeneXpert® instrument family is equipped with a Windows OS-based personal computer that is preloaded with software applications for running the tests and viewing the results, as described in Table 1.
The provided document is a 510(k) summary for the Cepheid Xpert C. difficile/Epi test. It details the device's characteristics, intended use, and performance studies conducted to demonstrate substantial equivalence to a predicate device and compliance with special controls.
Here's a breakdown of the requested information based on the provided text:
1. A table of acceptance criteria and the reported device performance
The document does not explicitly state formal acceptance criteria with numerical targets (e.g., minimum sensitivity/specificity percentages). Instead, it summarizes "verification studies" to demonstrate performance and compliance. The key performance indicators mentioned relate to agreement with expected results and accurate identification of strains.
| Acceptance Criteria (Implied) | Reported Device Performance |
|---|---|
| Maximum acceptable hold time for a prepared cartridge | Verified as 4 hours under all tested environments (ambient, elevated with high humidity, high temperatures). |
| Equivalent performance across different GeneXpert instruments/software | Functional testing showed 100% agreement with expected results and no statistically significant differences in Ct values among test runs in all instrument/software combinations (GeneXpert Dx System, GeneXpert Infinity System running GeneXpert Dx v6.5 and GeneXpert Xpertise v6.8/v7.1). |
| Accurate identification of C. difficile strains (Inclusivity) | Accurately identified all 26 strains of toxigenic C. difficile tested, demonstrating an inclusivity rate of 100%. |
| Compliance with Class II Special Controls Guidelines | The device met the requirements of the Class II Special Controls and accurately identified all strains of toxigenic C. difficile tested. |
2. Sample sized used for the test set and the data provenance (e.g. country of origin of the data, retrospective or prospective)
- Sample Size for Test Set:
- Prepared Cartridge Hold Time Study: Not explicitly stated how many "contrived positive" and "negative" samples were used, only that they were held for "various times under three (3) hold environments."
- Functional Testing: Not explicitly stated how many "contrived positive" and "negative" samples were used.
- Inclusivity Study: 26 C. difficile strains were tested (18 from previous study K110203 and 8 additional strains for K243730).
- Data Provenance: The document does not specify the country of origin of the data or whether the studies were retrospective or prospective. The studies mentioned (Hold Time, Functional Testing, Inclusivity) appear to be laboratory-based verification studies, rather than clinical trials with patient samples.
3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts (e.g. radiologist with 10 years of experience)
The document does not mention the use of experts to establish ground truth for the test set. The performance studies appear to be analytical verification studies using contrived samples and known bacterial strains, implying that the ground truth for these studies was established by laboratory methods rather than expert consensus on clinical samples.
4. Adjudication method (e.g. 2+1, 3+1, none) for the test set
The document does not describe any adjudication method for establishing ground truth, as the studies are analytical verification studies using controlled samples with known statuses (contrived positive/negative, specific C. difficile strains).
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
A multi-reader multi-case (MRMC) comparative effectiveness study was not done. The device is a diagnostic assay (Nucleic Acid Amplification Test) for infectious disease, not an AI-powered image analysis tool requiring human reader interpretation. No mention of AI assistance or human readers is present.
6. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done
Yes, the studies described (Prepared Cartridge Hold Time, Functional Testing, Inclusivity) assess the performance of the Xpert C. difficile/Epi test in a standalone manner. The device is an automated in vitro diagnostic test that performs sample preparation, amplification, and real-time detection without human intervention in the result determination process. It's an "algorithm-only" performance in the sense that the instrument provides a final result based on its internal processes.
7. The type of ground truth used (expert consensus, pathology, outcomes data, etc)
The ground truth for the verification studies was based on:
- Known status of contrived samples: "contrived positive (C. difficile cells added to negative matrix) and negative (negative matrix only) samples" for hold time and functional testing.
- Known bacterial strains: "C. difficile strains selected to broadly represent the majority of C. difficile toxinotypes encountered in practice" for the inclusivity study, where accurate identification of these known strains served as the ground truth.
8. The sample size for the training set
The document does not mention a "training set" in the context of machine learning or AI. This is a diagnostic assay, and its development likely involved traditional analytical validation and verification rather than an AI model requiring a training set.
9. How the ground truth for the training set was established
Not applicable, as no training set (in the AI/ML sense) is mentioned or implied for this device.
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