(90 days)
Not Found
No
The description focuses on automated PCR processes and real-time detection, with no mention of AI or ML algorithms for analysis or interpretation.
No.
This device is an in vitro diagnostic test intended to aid in the diagnosis of C. difficile infection (CDI) by detecting the tcdB gene, not to treat or cure a disease.
Yes
The device is explicitly stated as an "automated, qualitative in vitro diagnostic test" intended "as an aid in the diagnosis of CDI in humans."
No
The device is a system that includes both hardware (cobas® Liat® Analyzer, single-use disposable assay tube) and software. The software controls the hardware components to perform the test.
Yes, this device is an IVD (In Vitro Diagnostic).
Here's why:
- Intended Use/Indications for Use: The very first sentence explicitly states: "The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System is an automated, qualitative in vitro diagnostic test..." This directly identifies the device as an IVD.
- Device Description: The description further reinforces this by stating, "The cobas® Liat® System is for in vitro diagnostic use."
- Function: The device is designed to detect the presence of genetic material (DNA) in a biological sample (stool) to aid in the diagnosis of a medical condition (CDI). This is a core function of an IVD.
- Clinical Performance Evaluation: The document includes a detailed description of a clinical performance evaluation comparing the device's results to a reference method (culture) using human specimens. This type of evaluation is standard for IVDs to demonstrate their accuracy and reliability for diagnostic purposes.
N/A
Intended Use / Indications for Use
The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System is an automated, qualitative in vitro diagnostic test, that utilizes real-time polymerase chain reaction (PCR), for the detection of the toxin B (tcdB) gene of toxigenic Clostridium difficile in unformed (liquid or soft) stool specimens suspected of having C. difficile infection (CDI). The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System is intended for use as an aid in the diagnosis of CDI in humans in conjunction with clinical and epidemiological risk factors.
Product codes (comma separated list FDA assigned to the subject device)
OZN, OOI
Device Description
The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System (cobas® Cdiff ) is a rapid, automated in vitro diagnostic test for the qualitative detection of C. difficile DNA in human stool specimens.
The cobas® Liat® System is for in vitro diagnostic use. The system is designed to identify and/or measure the presence of genetic material in a biological sample. The system automates all nucleic acid amplification test (NAAT) processes, including reagent preparation, target enrichment, inhibitor removal, nucleic acid extraction, amplification, real-time detection, and result interpretation in a rapid manner.
The cobas® Cdiff test detects the tcdB target-specific oligonucleotide sequences. Toxin B (or tcdB) is a major toxin that is implicated in C. difficile pathogenesis and allows the differentiation between toxigenic and non-toxigenic C. difficile strains. Primers and probe oligonucleotide sequences were designed to detect C. difficile conserved sequences without cross-reacting with other Clostridium genus organisms, as well as with organisms commonly found in normal gut flora.
The cobas® Cdiff test uses silica magnetic particle-based nucleic acid extraction and TaqMan probe-based real-time PCR amplification and detection. The cobas® Liat® Analyzer automates and integrates sample purification, nucleic acid amplification and detection of the target sequence in biological samples. Other than adding the sample to the cobas® Cdiff assay tube, no reagent preparation or additional steps are required. The cobas® Liat® System consists of an cobas® Liat® Analyzer with integrated software for running tests and analyzing the results, and a single-use disposable cobas® Cdiff assay tube that holds all of the sample purification and PCR reagents and hosts the sample preparation and PCR processes specific for the Cdiff analyte. The test uses the assay tube as both the sample and reaction vessel. The assay tube comprises flexible tubing containing all required unit dose reagents pre-packed in tube segments, separated by pressure-sensitive seals, in the order of reagent use.
During the testing process, multiple sample processing actuators of the analyzer compress the cobas® Cdiff assay tube to selectively release reagents from tube segments, move the sample from one segment to another, and control reaction conditions such as reaction volume, temperature, pressure, and incubation time. Precise control of all these parameters provides optimal conditions for assay reactions, allowing the test to achieve high performance similar to or better than that of currently available molecular assays. The cobas® Liat® Analyzer software controls and coordinates these actions to perform all required assay processes, including sample preparation, nucleic acid extraction, target enrichment, inhibitor removal, nucleic acid elution, and real-time PCR. All assay steps are performed within the closed and self-contained cobas® Cdiff assay tube, thereby eliminating the potential for cross-contamination between samples. The collected data are automatically analyzed and the result is displayed in the assay report on the integrated LCD touch screen of the cobas® Liat® Analyzer.
Mentions image processing
Not Found
Mentions AI, DNN, or ML
Not Found
Input Imaging Modality
Not Found
Anatomical Site
Unformed (liquid or soft) stool specimens
Indicated Patient Age Range
Not Found (median age of 59 years, range 5 to 98 in clinical study but not an indication.)
Intended User / Care Setting
For prescription use
Description of the training set, sample size, data source, and annotation protocol
Not Found
Description of the test set, sample size, data source, and annotation protocol
A multi-site investigation (2 external sites, 1 internal site) using simulated clinical samples evaluated across reagent lot, site, operator, and testing day. Overall, 818 tests were performed in this study, out of which 798 were valid for the study and included in the final percent agreement analysis.
Panels consisted of 3 members: 1 negative specimen and 2 specimens with different concentrations of 1 strain of toxigenic C. difficile – the first a low positive concentration at ~ 1 x limit of detection (LOD) and the second a moderate positive at ~3 x LOD. There were 3 replicates per panel member; testing of 1 replicate sample was 1 test. A run was defined as testing of 3 replicates of a panel member. For each of 3 lots, panels were run on 5 different nonconsecutive days by 2 different operators at each of the 3 sites.
Summary of Performance Studies (study type, sample size, AUC, MRMC, standalone performance, key results)
Study Type: Non-clinical Analytical Performance Evaluation (Analytical Sensitivity, Inclusivity, Analytical Specificity/Cross-reactivity, Interference) and Clinical Performance Evaluation (Reproducibility, Clinical Performance).
Sample Size:
- Analytical Sensitivity (LOD): 2 toxigenic C. difficile strains (ATCC 43255, R12087), 5-member test panels.
- Inclusivity: 37 toxigenic strains, 3 replicates per strain.
- Analytical Specificity (Cross-reactivity): 146 non-toxigenic strains (toxinotype XI) of Clostridium difficile, human genomic DNA, and other microorganisms (total 149 samples mentioned in Table 4).
- Interference: 38 commonly used medications, fecal fat, whole blood, and mucin. Two toxigenic C. difficile isolates spiked to 3xLOD as targets.
- Reproducibility: 818 tests performed, 798 valid tests included in analysis.
- Clinical Performance: 1,013 evaluable fresh remnant stool specimens from patients (483 males, 530 females).
AUC, MRMC, standalone performance: Not applicable.
Key results:
- Analytical Sensitivity (LOD): LOD for ATCC 43255 was 90 CFU/swab; LOD for R12087 (CD196) was 45 CFU/swab.
- Inclusivity: All 37 toxigenic strains were detected with a 100% hit rate.
- Analytical Specificity (Cross-reactivity): The cobas® Liat Cdiff Test did not cross react with Cdiff non-toxigenic (toxinotype XI) strains, human epithelial cells, or other microorganisms tested. Presence of these potential cross-reactants did not interfere with detection of toxigenic Cdiff strains.
- Interference: Various substances tested did not show interference at specified concentrations (e.g., Fecal Fat up to 39% (w/v), Whole blood up to 100% (v/v), Mucin up to 50% (w/v)).
- Reproducibility:
- Overall percent agreement for ~1xLOD (low positive) was 98.5% (95% CI: 96.2%, 99.4%).
- Overall percent agreement for ~3xLOD (moderate positive) was 99.3% (95% CI: 97.3%, 99.8%).
- Overall percent agreement for negative panel member was 100.0% (95% CI: 98.6%, 100.0%).
- Total CV (%) for Ct values was ≤ 1.9% for all positive panel members.
- Clinical Performance (compared to combined direct and broth enrichment toxigenic culture):
- Sensitivity: 87.2% (156/179; 95% CI: 81.5% to 91.3%)
- Specificity: 98.1% (818/834; 95% CI: 96.9% to 98.8%)
- PPV: 90.7% (156/172; 95% CI: 85.4% to 94.2%)
- NPV: 97.3% (818/841; 95% CI: 95.9% to 98.2%)
- Clinical Performance (compared to direct culture):
- PPA: 94.6% (139/147; 95% CI = 89.6% to 97.2%)
- NPA: 96.2% (833/866; 95% CI = 94.7% to 97.3%)
Key Metrics (Sensitivity, Specificity, PPV, NPV, etc.)
Compared to Combined Direct and Broth Enrichment Culture:
- Sensitivity: 87.2% (156/179; 95% CI = 81.5% to 91.3%)
- Specificity: 98.1% (818/834; 95% CI = 96.9% to 98.8%)
- PPV: 90.7% (156/172; 95% CI = 85.4% to 94.2%)
- NPV: 97.3% (818/841; 95% CI = 95.9% to 98.2%)
Compared to Direct Culture:
- PPA: 94.6% (139/147; 95% CI = 89.6% to 97.2%)
- NPA: 96.2% (833/866; 95% CI = 94.7% to 97.3%)
Predicate Device(s)
cobas® Cdiff Test on the cobas® 4800 system
Reference Device(s)
Not Found
Predetermined Change Control Plan (PCCP) - All Relevant Information
Not Found
§ 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.
0
Public Health Service
Food and Drug Administration 10903 New Hampshire Avenue Document Control Center - WO66-G609 Silver Spring, MD 20993-0002
September 12, 2017
Roche Molecular Systems, Inc. Clare Santulli Senior Manager 4300 Hacienda Drive Pleasanton, California 94588-2722
Re: K171770
Trade/Device Name: cobas Cdiff Nucleic acid test for use on the cobas Liat System Regulation Number: 21 CFR 866.3130 Regulation Name: Clostridium difficile toxin gene amplification assay Regulatory Class: Class II Product Code: OZN, OOI Dated: June 13, 2017 Received: June 14, 2017
Dear Clare Santulli:
We have reviewed your Section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food, Drug, and Cosmetic Act (Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. The general controls provisions of the Act include requirements for annual registration. Isting of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.
If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.
Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Part 801 and Part 809); medical device reporting of medical device-related adverse events) (21 CFR 803); good manufacturing practice requirements
1
as set forth in the quality systems (OS) regulation (21 CFR Part 820); and if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR 1000-1050.
If vou desire specific advice for your device on our labeling regulation (21 CFR Part 801 and Part 809), please contact the Division of Industry and Consumer Education (DICE) at its toll-free number (800) 638-2041 or (301) 796-7100 or at its Internet address
http://www.fda.gov/MedicalDevices/ResourcesforYou/Industry/default.htm. Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR Part 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part 803), please go to
http://www.fda.gov/MedicalDevices/Safety/ReportaProblem/default.htm for the CDRH's Office of Surveillance and Biometrics/Division of Postmarket Surveillance.
You may obtain other general information on your responsibilities under the Act from the Division of Industry and Consumer Education (DICE) at its toll-free number (800) 638-2041 or (301) 796-7100 or at its Internet address
http://www.fda.gov/MedicalDevices/ResourcesforYou/Industry/default.htm.
Sincerely,
Ribhi Shawar -S For
Uwe Scherf, M.Sc., Ph.D. Director Division of Microbiology Devices Office of In Vitro Diagnostics and Radiological Health Center for Devices and Radiological Health
Enclosure
2
Indications for Use
510(k) Number (if known) K171770
Device Name
cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System
Indications for Use (Describe)
The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System is an automated, qualitative in vitro diagnostic test, that utilizes real-time polymerase chain reaction (PCR), for the detection of the toxin B (tcdB) gene of toxigenic Clostridium difficile in unformed (liquid or soft) stool specimens suspected of having C. difficile infection (CDI). The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System is intended for use as an aid in the diagnosis of CDI in humans in conjunction with clinical and epidemiological risk factors.
| Type of Use (Select one or both, as applicable) | |
|---|---|
| × Prescription Use (Part 21 CFR 801 Subpart D) | Over-The-Counter Use (21 CFR 801 Subpart C) |
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3
510(k) Summary
| Submitter Name | Roche Molecular Systems, Inc. |
|---|---|
| Address | 4300 Hacienda Drive |
| Pleasanton, CA 94588-2722 | |
| Contact | Clare Santulli |
| Phone: (925) 730-8886 | |
| FAX: (925) 225-0207 | |
| Email: clare.santulli@roche.com | |
| Date Prepared | September 11, 2017 |
| Proprietary Name | cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System |
| Common Name | Clostridium difficile Test |
| Classification Name | 21 CFR 866.3130 - Clostridium difficile toxin gene amplification assay |
| 21 CFR 862.2570 - Real Time Nucleic Acid Amplification System | |
| Product Codes | OZN, OOI |
| Predicate Devices | cobas® Cdiff Test on the cobas® 4800 system |
| Establishment Registration | Branchburg: 2243471 |
| Pleasanton: 3004141078 | |
| Indianapolis: 1823260 |
4
1. DEVICE DESCRIPTION
The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System (cobas® Cdiff ) is a rapid, automated in vitro diagnostic test for the qualitative detection of C. difficile DNA in human stool specimens.
The cobas® Liat® System is for in vitro diagnostic use. The system is designed to identify and/or measure the presence of genetic material in a biological sample. The system automates all nucleic acid amplification test (NAAT) processes, including reagent preparation, target enrichment, inhibitor removal, nucleic acid extraction, amplification, real-time detection, and result interpretation in a rapid manner.
1.1. Target Selection
The cobas® Cdiff test detects the tcdB target-specific oligonucleotide sequences. Toxin B (or tcdB) is a major toxin that is implicated in C. difficile pathogenesis and allows the differentiation between toxigenic and non-toxigenic C. difficile strains. Primers and probe oligonucleotide sequences were designed to detect C. difficile conserved sequences without cross-reacting with other Clostridium genus organisms, as well as with organisms commonly found in normal gut flora.
1.2. Test Principle
The cobas® Cdiff test uses silica magnetic particle-based nucleic acid extraction and TaqMan probe-based real-time PCR amplification and detection. The cobas® Liat® Analyzer automates and integrates sample purification, nucleic acid amplification and detection of the target sequence in biological samples. Other than adding the sample to the cobas® Cdiff assay tube, no reagent preparation or additional steps are required. The cobas® Liat® System consists of an cobas® Liat® Analyzer with integrated software for running tests and analyzing the results, and a single-use disposable cobas® Cdiff assay tube that holds all of the sample purification and PCR reagents and hosts the sample preparation and PCR processes specific for the Cdiff analyte. The test uses the assay tube as both the sample and reaction vessel. The assay tube comprises flexible tubing containing all required unit dose reagents pre-packed in tube segments, separated by pressure-sensitive seals, in the order of reagent use.
5
During the testing process, multiple sample processing actuators of the analyzer compress the cobas® Cdiff assay tube to selectively release reagents from tube segments, move the sample from one segment to another, and control reaction conditions such as reaction volume, temperature, pressure, and incubation time. Precise control of all these parameters provides optimal conditions for assay reactions, allowing the test to achieve high performance similar to or better than that of currently available molecular assays. The cobas® Liat® Analyzer software controls and coordinates these actions to perform all required assay processes, including sample preparation, nucleic acid extraction, target enrichment, inhibitor removal, nucleic acid elution, and real-time PCR. All assay steps are performed within the closed and self-contained cobas® Cdiff assay tube, thereby eliminating the potential for cross-contamination between samples. The collected data are automatically analyzed and the result is displayed in the assay report on the integrated LCD touch screen of the cobas® Liat® Analyzer.
2. INDICATIONS FOR USE
The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System is an automated, qualitative in vitro diagnostic test, that utilizes real-time polymerase chain reaction (PCR), for the detection of the toxin B (tcdB) gene of toxigenic Clostridium difficile in unformed (liquid or soft) stool specimens obtained from patients suspected of having C. difficile infection (CDI). The cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System is intended for use as an aid in the diagnosis of CDI in humans in conjunction with clinical and epidemiological risk factors.
TECHNOLOGICAL CHARACTERISTICS 3.
The primary technological characteristics and intended use of the RMS cobas® Cdiff Nucleic acid test for use on the cobas Liate System are substantially equivalent to other legally marketed nucleic acid amplification tests intended for the qualitative detection of Clostridium difficile. As indicated in Table 1, the RMS cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System is substantially equivalent to significant characteristics of the identified predicate device, the currently cleared cobas® Cdiff Test for use on the cobas® 4800 System, 510(k) 142422. The predicate device and the submitted device both utilize the cobas® PCR Media Uni Swab Sample Kit for specimen transfer into cobas PCR Media.
6
| | Submitted Device:
cobas® Cdiff Nucleic acid test for use
on the cobas® Liat® System | Predicate Device:
cobas® Cdiff Test for use on the cobas®
4800 System , K142422 |
|-------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Intended Use | The cobas® Cdiff Nucleic acid test for use
on the cobas® Liat® System is an
automated, qualitative in vitro diagnostic
test, that utilizes real-time polymerase
chain reaction (PCR), for the detection of
the toxin B (tcdB) gene of toxigenic
Clostridium difficile in unformed (liquid or
soft) stool specimens obtained from
patients suspected of having C. difficile
infection (CDI). The cobas® Cdiff Nucleic
acid test for use on the cobas® Liat®
System is intended for use as an aid in the
diagnosis of CDI in humans in conjunction
with clinical and epidemiological risk
factors. | The cobas® Cdiff Test on the
cobas® 4800 system is an automated,
qualitative in vitro diagnostic test, that
utilizes real-time polymerase chain
reaction (PCR), for the direct detection of
the toxin B (tcdB) gene of toxigenic
Clostridium difficile in unformed (liquid or
soft) stool specimens obtained from
patients suspected of having C. difficile
infection (CDI). The cobas® Cdiff Test is
intended for use as an aid in the diagnosis
of CDI in humans in conjunction with
clinical and epidemiological risk factors. |
| Conditions for use | For prescription use | Same |
| Regulation Number,
Classification and
Subsequent Product
Codes | 21 CFR 866.2660: Microorganism
differentiation and identification device.
OMN: C. difficile Nucleic Acid
Amplification Test Assay.
OOI: Real Time Nucleic Acid
Amplification System. | Same |
| Sample Types | Unformed soft stool specimens | Same |
| Amplification Technology | Real-time PCR | Same |
| Detection Technology | TaqMan probes with fluorescent dyes | Same |
| Internal Control | A gram-positive Bacillus thuringiensis israelensis bacterial organism to monitor
the full process on the cobas® Liat®
Analyzer. Native sequence in the bacteria
is used as the Internal Control target. | Lambda phage with encapsulated internal
control sequence |
| Positive Control | Plasmid in buffer | Same |
| Negative Control | Buffer only | Same |
| Analyte Targets | Toxin B ( tcdB ) gene | Same |
| Sample Transfer Devices | cobas® PCR Media Uni Swab Sample Kit | Same |
| Sample Preparation | Magnetic bead-based nucleic acid
extraction automated by
cobas® Liat® Analyzer | Magnetic bead-based nucleic acid
extraction automated by
cobas® 4800 System |
| Result Analysis | Based on PCR cycle threshold analysis | Same |
| Subject Status | Symptomatic | Same |
Similarities and Differences between the cobas® Cdiff Nucleic acid test for use Table 1: on the cobas® Liat® System and the Predicate Device
7
NON-CLINICAL PERFORMANCE EVALUATION 4.
4.1. Analytical Sensitivity
The analytical sensitivity (Limit of Detection or LOD) for the cobas® Cdiff test was determined by analyzing 2 toxigenic C. difficile strains ATCC 43255(VPI 10463) and R12087 (CDI 196). Five-member test panels were prepared with the two different strains of Cdiff at concentrations that bracketed the expected Limit of Detection (LOD). Replicates of each test panel member were then tested with two different lots of cobas® Liat® Cdiff assay tubes to determine the Limit of Detection, or the lowest Cdiff concentration to yield a Hit Rate of at least 95%, where all higher concentrations also have a Hit Rate of ≥ 95%. Additional replicates were tested to confirm the LOD.
Negative stool background samples were also run to verify the Limit of Blank (LoB).
The LOD results among 2 reagent lots are shown in Table 2.
LOD cobas® Cdiff Nucleic acid test for use on the cobas® Liat® System Table 2:
| Strain ID | Toxinotype | REA*
Type | PFG†
Type | Ribotype | Phenotype | LOD
(CFU/swab) |
|---------------------------|------------|--------------|--------------|----------|-----------|-------------------|
| ATCC 43255
(VPI 10463) | 0 | N/A | N/A | 87 | A+B+CDT- | 90 |
| R12087 (CD196) | III | BI | NAP1 | 27 | A+B+CDT+ | 45 |
*Restriction endonuclease analysis; *Pulse Field Gel
4.2. Inclusivity
The limit of detection of cobas Cdiff test on 37 toxigenic strains representing additional toxinotypes was verified by testing three replicates per strain at three times the LOD level (~60 CFU/ml equivalent to 270 CFU/swab) of ATCC 43255.
All 37 toxigenic strains were detected with a 100% hit rate for each toxigenic strain in this study, confirming that the cobas Cdiff test can detect these C. difficile toxinotypes. Results are shown in Table 3.
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| Sample ID | Cdiff Strain | Toxinotype | Ribotype |
|---|---|---|---|
| 1 | RMSCC 11251 | ||
| (ATCC#BAA-1382; 630) | 0 | 012 | |
| 2 | EX 623 | I | 102 |
| 3 | AC 008 | II | 103 |
| 4 | RMSCC 12827 [2004118; CDC-204118 (NAP-1)] | III | 027 |
| 5 | SE 844 | IIIa | 080 |
| 6 | CH6230 | IIIc | N/A |
| 7 | RMSCC 11298 (P43) | IV | N/A |
| 8 | 55767 | IV | 023 |
| 9 | RMSCC 11300 (2748-06) | V | 078 |
| 10 | SE 881 | V | 045 |
| 11 | RMSCC 11302 (SE 1203) | VI | 033 |
| 12 | 57267 | VII | 063 |
| 13 | RMSCC 12472 | ||
| (ATCC# 43598; 1470) | VIII | 017 | |
| 14 | RMSCC 11299 (51680) | IX | 019 |
| 15 | RMSCC 11304 (CCUG 8864/STCC20309) | X | 036 |
| 16 | RMSCC 11308 (F15) | XII | N/A |
| 17 | IS 25 | XII | 056 |
| 18 | R 9367 | XIII | 070 |
| 19 | R 10870 | XIV | |
| (New-XIVa) | 111 | ||
| 20 | R 9385 | XV | |
| (New XIVb) | 122 | ||
| 21 | SUC36 | XVI | 078 |
| 22 | RMSCC 11309 (No 1313) | XVII | 232 |
| 23 | K095 | XVIII | 014 |
| 24 | TR13 | XIX | N/A |
| 25 | TR14 | XX | N/A |
| 26 | CH6223 | XXI | N/A |
| 27 | CD07-468 | XXII | N/A |
| 28 | 8785 | XXIII | |
| (New-IXc) | N/A | ||
| 29 | 597B | XXIV | 131 |
| 30 | 7325 | XXV | 027 |
| 31 | 7459 | XXVI | N/A |
| 32 | KK2443/2006 | XXVII | N/A |
| 33 | CD08-070 | XXVIII | 126 |
| 34 | CD07-140 | XXIX | 056 |
| 35 | ES 130 | XXX | N/A |
| 36 | WA 151 | XXXI | N/A |
| 37 | 173070 | XXXII | N/A |
Table 3: Results of Testing Three Replicates of 40 Cdiff Strains at 60CFU/mL (~3x LOD)
9
Analytical Specificity (Cross-reactivity) 4.3.
The cobas Liat Cdiff test was examined for analytical specificity by testing 146 non-toxigenic strains (toxinotype XI) of Clostridium difficile, human genomic DNA, and other microorganisms which could be present in clinical stool specimens at ~3xLOD concentration.
Test panels were prepared that contained each of these microorganisms, and each test panel was tested with the cobas Liat® Cdiff assay tubes. The microorganism concentrations that were tested correspond to approximately 1E+06 units (CFU, IFU, cells) per mL of stool specimen for bacteria and human epithelial cells (as a source for human genomic DNA) and 1E+05 TCID50and/or PFU per mL of stool specimen for viruses.
Three non-toxigenic Cdiff strains (toxinotype XI) tested during inclusivity study [RMSCC # 11305 (ES 1103), 11306 (6035/06) and 12414 (F14)] were not detected by the cobas® Cdiff test are included in this section.
The cobas® Liat Cdiff Test did not cross react with Cdiff non-toxigenic (toxinotype XI) strains, human epithelial cells (tested as a source of human genomic DNA) or other microorganisms which could be present in clinical stool specimens and that were tested in the study. Further, the presence of any of these potential cross reactants tested did not interfere with detection of toxigenic Cdiff strains tested at approximately 3x LOD level.
All 149 non-toxigenic strains (toxinotype XI) of Clostridium difficile, human genomic DNA, and other microorganisms are listed in Table 4.
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| Organism / Cell
| Number | Organism / Cell Name: | Source# |
|---|---|---|
| 1 | Abiotrophia defectiva | ATCC# 49176 |
| 2 | Acinetobacter baumannii | ATCC# 19606 |
| 3 | Acinetobacter Iwoffii | ATCC# 15309 |
| 4 | Aeromonas hydrophila | ATCC# 7966 |
| 5 | Alcaligenes faecalis | ATCC# 35655 |
| 6 | Alcaligenes faecalis subsp. Faecalis | ATCC# 8750 |
| 7 | Alcaligenes faecalis subsp. Faecalis | ATCC# 15554 |
| 8 | Anaerococcus tetradius | ATCC# 35098 |
| 9 | Bacillus cereus | ATCC# 13472 |
| 10 | Bacillus cereus | ATCC# 11778 (also known as HER 1414) |
| 11 | Bacteroides caccae | ATCC# 43185 |
| 12 | Bacteroides fragilis | ATCC# 25285 |
| 13 | Bacteroides merdae | ATCC# 43184 |
| 14 | Bacteroides stercoris | ATCC# 43183 |
| 15 | Bifidobacterium adolescentis | ATCC# 15703 |
| 16 | Bifidobacterium longum | ATCC# 15707 |
| 17 | Campylobacter coli | ATCC# 33559 |
| 18 | Campylobacter jejuni (f.k.a Campylobacter coli) | ATCC# 43479 |
| 19 | Campylobacter jejuni Subsp. jejuni | ATCC# 33292 |
| 20 | Candida albicans | ATCC# 10231 |
| 21 | Candida catenulata | ATCC# 10565 |
| 22 | Cedecea davisae | ATCC# 33431 |
| 23 | Chlamydia Trachomatis Serovar L2 | Zeptometrix # 0801776 |
| 24 | Citrobacter amalonaticus | ATCC# 25405 |
| 25 | Citrobacter freundii | ATCC# 8090 |
| 26 | Citrobacter koseri | ATCC# 27028 |
| 27 | Citrobacter sedlakii | ATCC# 51115 |
| 28 | Clostridium beijerinckii | ATCC# 8260 |
| 29 | Clostridium bifermentans | ATCC# 638 |
| 30 | Clostridium bolteae | ATCC# BAA-613 |
| 31 | Clostridium butyricum | ATCC# 19398 |
| 32 | Clostridium chauvoei | ATCC# 11957 |
| 33 | Clostridium difficile (Non-toxigenic, Serogroup B) | ATCC# 43593 |
| 34 | Clostridium difficile (Non-toxigenic, Serogroup I) | ATCC# 43601 |
| 35 | Clostridium fallax | ATCC# 19400 |
| 36 | Clostridium haemolyticum | ATCC# 9650 |
| 37 | Clostridium histolyticum | ATCC# 19401 |
| 38 | Clostridium innocuum | ATCC# 14501 |
| 39 | Clostridium methylpentosum | ATCC# 43829 |
| 40 | Clostridium nexile | ATCC# 27757 |
| 41 | Clostridium novyi | ATCC# 19402 |
| 42 | Clostridium orbiscindens (re-named | |
| Flavonifractor plautii) | ATCC# 49531 | |
| Organism / Cell | ||
| Number | Organism / Cell Name: | Source# |
| 43 | Clostridium paraputrificum | ATCC# 17796 |
| 44 | Clostridium perfringens | ATCC# 13124 |
| 45 | Clostridium ramosum | ATCC# 25582 |
| 46 | Clostridium scindens | ATCC# 35704 |
| 47 | Clostridium septicum | ATCC# 12464 |
| 48 | Clostridium sordellii | ATCC# 9714 |
| 49 | Clostridium sphenoides | ATCC# 19403 |
| 50 | Clostridium spiroforme | ATCC# 29899 |
| 51 | Clostridium sporogenes | CCRI# 11128 |
| 52 | Clostridium sporogenes | ATCC# 15579 |
| 53 | Clostridium symbiosum | ATCC# 14940 |
| 54 | Clostridium tertium | DSMZ# 662 |
| 55 | Clostridium tetani | ATCC# 19406 |
| 56 | Collinsella aerofaciens | ATCC# 25986 |
| 57 | Corynebacterium genitalium | ATCC# 33030 |
| 58 | Cytomegalovirus (AD-169) | ZeptoMetrix # 0810003CF |
| 59 | Desulfovibrio piger | ATCC# 29098 |
| 60 | Edwardsiella tarda | ATCC# 15947 |
| 61 | Eggerthella lenta | ATCC# 25559 |
| 62 | Enterobacter aerogenes | ATCC# 13048 |
| 63 | Enterobacter cloacae | ATCC# 13047 |
| 64 | Enterococcus casseliflavus | ATCC# 25788 |
| 65 | Enterococcus cecorum | ATCC# 43198 |
| 66 | Enterococcus dispar | ATCC# 51266 |
| 67 | Enterococcus faecalis Van B | ATCC# 51299 |
| 68 | Enterococcus faecium Van A | ATCC# 35667 |
| 69 | Enterococcus gallinarum Van C | ATCC# 49573 |
| 70 | Enterococcus hirae | ATCC# 8043 |
| 71 | Enterococcus raffinosus | ATCC# 49427 |
| 72 | Escherichia coli | ATCC# 11775 |
| 73 | Escherichia coli | ATCC# 25922 |
| 74 | Escherichia coli O157:H7 | ATCC# 700927 |
| 75 | Escherichia fergusonii | ATCC# 35469 |
| 76 | Escherichia hermannii | ATCC# 33650 |
| 77 | Fusobacterium varium | ATCC# 8501 |
| 78 | Gardnerella vaginalis | ATCC# 14018 |
| 79 | Gemella morbillorum | ATCC# 27824 |
| 80 | Hafnia alvei | CMCC# 147 |
| 81 | HCT-15 Human Cells | ATCC# CCL-225 |
| 82 | Helicobacter fennelliae | ATCC# 35683 |
| 83 | Helicobacter pylori | ATCC# 43504 |
| 84 | Human Adenovirus 41 | ZeptoMetrix # 0810085CF |
| 85 | Human Coxsackievirus A4 | ZeptoMetrix # 0810142CF |
| 86 | Human Coxsackievirus B4 | ZeptoMetrix # 0810075CF |
| 87 | Human Echovirus 11 | ZeptoMetrix # 0810023CF |
| Organism / Cell | ||
| Number | Organism / Cell Name: | Source# |
| 88 | Human Enterovirus 71 | ZeptoMetrix # 0810236CF |
| 89 | Human Rotavirus | ZeptoMetrix # 0810041CF |
| 90 | Klebsiella oxytoca | ATCC# 33496 |
| 91 | Klebsiella pneumoniae subsp. Pneumoniae | ATCC# 13883 |
| 92 | Lactobacillus acidophilus | ATCC# 4356 |
| 93 | Lactobacillus reuteri | ATCC# 23272 |
| 94 | Lactococcus lactis | ATCC# 19435 |
| 95 | Leminorella grimontii | ATCC# 33999 |
| 96 | Listeria grayi | ATCC# 19120 |
| 97 | Listeria innocua | ATCC# 33090 |
| 98 | Listeria monocytogenes | ATCC# 15313 |
| 99 | Listeria monocytogenes | ATCC# BAA-839 |
| 100 | Mitsuokella multacida | ATCC# 27723 |
| 101 | Mobiluncus curtisii | ATCC# 35241 |
| 102 | Molellerella wisonsensis | ATCC# 35017 |
| 103 | Morganella morganii | ATCC# 25830 |
| 104 | Neiserria gonorrhoeae | ATCC# 35201 |
| 105 | Norovirus GII | ZeptoMetrix # 0810087CF |
| 106 | Peptoniphilus asaccharolyticus | ATCC# 14963 |
| 107 | Peptostreptococcus anaerobius | ATCC# 27337 |
| 108 | Plesiomonas shigelloides | ATCC# 14029 |
| 109 | Porphyromonas asaccharolytica | ATCC# 25260 |
| 110 | Prevotella melaninogenica | ATCC# 25845 |
| 111 | Proteus mirabilis | ATCC# 29906 |
| 112 | Proteus mirabilis | ATCC# 25933 |
| 113 | Proteus penneri | ATCC# 35198 |
| 114 | Providencia alcalifaciens | ATCC# 9886 |
| 115 | Providencia rettgeri | ATCC# 9250 |
| 116 | Providencia stuartii | ATCC# 29914 |
| 117 | Pseudomonas aeroginosa | ATCC# 35554 |
| 118 | Pseudomonas aeruginosa | ATCC# 33584 |
| 119 | Pseudomonas putida | ATCC# 12633 |
| 120 | Ruminococcus bromii | ATCC# 27255 |
| 121 | Salmonella enterica subsp. arizonae (f.k.a. | |
| Salmonella choleraesuis ssp. arizonae) | ATCC# 13314 | |
| 122 | Salmonella enterica subsp. enterica | CMCC# 1975 |
| 123 | Salmonella enterica subsp. enterica serovar | |
| Choleraesuis | ATCC# 7001 | |
| 124(^) | Salmonella enterica subsp. enterica serovar | |
| Typhi | ATCC# 19430 | |
| 125 | Salmonella enterica subsp.enterica serovar | |
| Typhimurium | ATCC# 14028 | |
| 126 | Serratia liquefaciens | CMCC# 169 |
| 127 | Serratia marcescens | ATCC# 8100 |
| 128 | Serratia marcescens | ATCC# 13880 |
| 129 | Serratia liquefaciens | ATCC# 27592 |
| Organism / Cell | ||
| Number | Organism / Cell Name: | Source# |
| 130 | Shigella boydii | ATCC# 9207 |
| 131 | Shigella dysenteriae | ATCC# 11835 |
| 132 | Shigella sonnei | ATCC# 29930 |
| 133 | Staphylococcus aureus | ATCC# 43300 |
| 134 | Staphylococcus epidermidis | ATCC# 14990 |
| 135 | Stenotrophomonas maltophilia | ATCC# 13637 |
| 136 | Streptococcus agalactiae | ATCC# 13813 |
| 137 | Streptococcus dysgalactiae | ATCC# 43078 |
| 138 | Streptococcus intermedius | ATCC# 27335 |
| 139 | Streptococcus sp.; strain V8 | ATCC# 12973 |
| 140 | Streptococcus uberis | ATCC# 19436 |
| 141 | Trabulsiella guamensis | ATCC# 49490 |
| 142 | Veillonella parvula | ATCC# 10790 |
| 143 | Vibrio cholerae | ATCC# 25870 |
| 144 | Vibrio parahaemolyticus | ATCC# 17802 |
| 145 | Yersinia bercovieri | ATCC# 43970 |
| 146 | Yersinia rohdei | ATCC# 43380 |
| 147 | Clostridium difficile (Non-toxigenic- Xla) | |
| (ES 1103)* | BMTU# 13799 (RMSCC 11305) | |
| 148 | Clostridium difficile (Non-toxigenic- Xia) | |
| (6035/06)* | BMTU#9961 (RMSCC 11306) | |
| 149 | Clostridium difficile (Non-toxigenic-Xlb) (F14)* | BMTU# 9962 (RMSCC 12414 and 11307) |
Table 4: All Cross Reactivity Panel Members
11
12
13
- Non-toxigenic Clostridium difficile (#147,148,149) were tested during Inclusivity study.
14
Interference 4.4.
Thirty eight commonly used medications, as well as fecal fat, whole blood, and mucin, were tested for potential interference effects with the cobas Cdiff test. All substances were tested at levels above what could be reasonably expected to be collected by a swab in a stool specimen. The amount of interference substance is expressed as concentration in primary stool specimen. Two toxigenic C. difficile isolates were spiked to 3 x Limit of Detection (LOD) of the cobas Cdiff test and used as targets in the tests. Exogenous substances at the highest tolerable concentration with no interference on cobas Cdiff test are shown in Table 5. Exogenous substances concentrations higher than listed in Table 5 may generate false negative or invalid results.
For fecal fat, no interference was observed up to 39% (w/v), and for mucin, no interference was observed up to 50% (w/v). For whole blood, no interference was observed up to 100% (v/v), which is equivalent to 100% of the capacity of the transfer swab. These results are summarized in Table 5.
| Substance | Primary Stool
Specimen
Concentration |
|------------------------|--------------------------------------------|
| Fecal Fat | 0.22% - 39% (w/v) |
| Whole blood | 100% (v/v) |
| Mucin | 50% (w/v) |
| Aleve | 100% (w/v) |
| Mylanta | 100% (w/v) |
| Anusol | 100% (w/v) |
| Dulcolax | 23% (w/v)* |
| Equate Laxative | 50% (w/v)* |
| Equate Hydrocortisone | 100% (w/v) |
| E-Z-HD Barium Sulfate | 100% (w/v) |
| Fleet | 100% (w/v) |
| Glycerin Suppositories | 100% (w/v) |
| Gravol Suppositories | 100% (w/v) |
| Gynol II Contraceptive | 10% (w/v)* |
| Imodium | 100% (w/v) |
| Kaopectate | 100% (w/v) |
| K-Y Jelly | 100% (w/v) |
| Metronidazole | 100% (w/v) |
Results from Interference Substances Testing Table 5:
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| Substance | Primary Stool
Specimen
Concentration |
|-------------------------------------|------------------------------------------------------------|
| Miconazole | 100% (w/v) |
| Mineral Oil | 100% (w/v) |
| Monistat Cream | 100% (w/v) |
| Monistat Complete Care | 100% (w/v) |
| Nystatin Ointment | 100% (w/v) |
| Palmitic Acid | 100% (w/v) |
| Pedia Lax | 100% (w/v) |
| Pepto Bismol | 25% (w/v)* |
| Witch Hazel | 50% (w/v)* |
| Preparation H Hemorrhoidal Cream | 100% (w/v) |
| Preparation H Hemorrhoidal ointment | 100% (w/v) |
| Dramamine | 12.5% (w/v)* |
| Steric Acid | 100% (w/v) |
| Docusate Sodium | 100% (w/v) |
| Tums | 50% (w/v)* |
| Mesalamine Rectal Suspension | 100% (w/v) |
| Vagisil Anti-itch Cream | 12.5% (w/v)* |
| Vancomycin | 100% (w/v) |
| Vaseline | 100% (w/v) |
| Sun Screen | 100% (w/v) |
| Monistat Vaginal Insert | 100% (w/v) |
| Vaginal Contraceptive Film | 1 film vortexed with
20 ml of primary stool
sample |
| Spermicidal Condoms | 1 Condom vortexed
with 20 mL of primary
stool sample |
5. CLINICAL PERFORMANCE EVALUATION
5.1. Reproducibility
The reproducibility of the cobas Cdiff test was established in a multi-site investigation (2 external sites, 1 internal site) using simulated clinical samples evaluated across reagent lot, site, operator, and testing day. Overall, 818 tests were performed in this study, out of which 798 were valid for the study and included in the final percent agreement analysis.
Panels consisted of 3 members: 1 negative specimen and 2 specimens with different concentrations of 1 strain of toxigenic C. difficile – the first a low positive concentration at ~ 1 x limit of detection (LOD) and the second a moderate positive at ~3 x LOD. There were
16
3 replicates per panel member; testing of 1 replicate sample was 1 test. A run was defined as testing of 3 replicates of a panel member. For each of 3 lots, panels were run on 5 different nonconsecutive days by 2 different operators at each of the 3 sites. Table 6 shows the percent agreement results by panel member concentration, negative percent agreement for negative panel members and positive percent agreement for positive panel members. For the ~1 x LOD panel members (low positive), the overall percent agreement was 98.5% with a lower bound of the two-sided 95% Score CI of 96.2%. Overall percent agreement was 99.3% for the ~3 x LOD panel member (moderate positive) and 100% for the negative panel member.
Percent Agreement by Panel Member Compared to Acceptance Criteria Table 6:
| Percent Agreement | ||||
|---|---|---|---|---|
| Panel Member | Number of Valid | |||
| Test Results | Estimate | (95% CI)* | Met | |
| Acceptance | ||||
| Criteria | ||||
| Negative | 262 | 100.0% (262/262) | (98.6%, 100.0%) | n/a |
| ~1xLOD | 266 | 98.5% (262/266) | (96.2%, 99.4%) | Yes |
| ~3xLOD | 270 | 99.3% (268/270) | (97.3%, 99.8%) | n/a |
- 95% CI = two-sided 95% Score binomial confidence interval.
Results were in agreement when a positive panel member had a valid result of Positive (Cdiff Detected) for the analyte orwhen the negative panel member had a valid result of Negative (Cdiff Not Detected) for the analyte. n/a = not applicable
Table 7 presents the mean, total standard deviation (SD), and total percent coefficient of variation (CV %) of Ct values by panel member concentration.
Table 7 also presents percent agreement separately by lot, site, operator, and testing day.
17
| Panel Member | Negative | ~1x LOD | ~3x LOD | |
|---|---|---|---|---|
| Number of Valid Test Results | 262 | 266 | 270 | |
| Overall Percent Agreement, % (n/N)* | ||||
| Percent | ||||
| Agreement | 100.0 | |||
| (262/262) | 98.5 | |||
| (262/266) | 99.3 | |||
| (268/270) | ||||
| Overall | 95% Score CI | (98.6, 100.0) | (96.2, 99.4) | (97.3, 99.8) |
| Percent Agreement for Component Variables, % (n/N)* | ||||
| Reagent Lot | 1 | 100.0 (85/85) | 100.0 (87/87) | 100.0 (90/90) |
| 2 | 100.0 (88/88) | 100.0 (90/90) | 100.0 (90/90) | |
| 3 | 100.0 (89/89) | 95.5 (85/89) | 97.8 (88/90) | |
| Site | 1 | 100.0 (85/85) | 100.0 (88/88) | 100.0 (90/90) |
| 2 | 100.0 (89/89) | 97.8 (87/89) | 98.9 (89/90) | |
| 3 | 100.0 (88/88) | 97.8 (87/89) | 98.9 (89/90) | |
| 1 | 100.0 (43/43) | 100.0 (44/44) | 100.0 (45/45) | |
| 2 | 100.0 (42/42) | 100.0 (44/44) | 100.0 (45/45) | |
| 3 | 100.0 (45/45) | 97.7 (43/44) | 100.0 (45/45) | |
| Operator | 4 | 100.0 (44/44) | 97.8 (44/45) | 97.8 (44/45) |
| 5 | 100.0 (44/44) | 100.0 (44/44) | 97.8 (44/45) | |
| 6 | 100.0 (44/44) | 95.6 (43/45) | 100.0 (45/45) | |
| Testing Day | 1 | 100.0 (53/53) | 100.0 (54/54) | 100.0 (54/54) |
| 2 | 100.0 (54/54) | 96.3 (52/54) | 100.0 (54/54) | |
| 3 | 100.0 (52/52) | 96.0 (48/50) | 98.1 (53/54) | |
| 4 | 100.0 (52/52) | 100.0 (54/54) | 98.1 (53/54) | |
| 5 | 100.0 (51/51) | 100.0 (54/54) | 100.0 (54/54) |
Table 7: Percent Agreement by Panel Member for Lot, Site, Operator and Testing Day
Note: CI = confidence interval.
- For the negative panel member: Percent agreement = (number of not detected results) x 100. For the positive panel members: Percent agreement = (number of detected results/total valid results) x 100.
Table 8 below presents the overall SD and percent CV (%) of Ct values for positive panel members at ~1 x LOD and ~3 x LOD concentrations, as well as the variance attributed to individual components (lot, site, operator, testing day, and within-run). Within-run variation refers to the variation within a 'study run' that consists of the 3 replicates for a given panel member processed by the same operator on the same analyzer on the same day.
Across all components, the total CV (%) was ≤ 1.9% with respect to the cycle threshold (Ct) value for all positive panel members. Within each component, the CV (%) was ≤ 1.6% across positive panel members.
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| Standard Deviation and Percent Coefficient of Variation | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Lot | Site | Operator | Day | Within-Run | Total | |||||||||
| Panel Member | N | Mean Ct | SD | CV | SD | CV | SD | CV | SD | CV | SD | CV | SD | CV |
| ~1xLOD | 262 | 31.4 | 0.13 | 0.4% | 0.26 | 0.8% | 0.00 | 0.0% | 0.13 | 0.4% | 0.51 | 1.6% | 0.60 | 1.9% |
| ~3xLOD | 268 | 30.0 | 0.23 | 0.8% | 0.25 | 0.8% | 0.08 | 0.3% | 0.00 | 0.0% | 0.38 | 1.3% | 0.51 | 1.7% |
Table 8: Overall Mean, Standard Deviation (SD) and Percent Coefficients of Variation (CV) for Ct Values from Valid Results for Positive Panel Members
5.2. Clinical Performance
The clinical performance of the cobas® Cdiff test was established in a prospective, multi-site investigation designed to evaluate the sensitivity and specificity of the cobas Cdiff test compared to the combined results of direct and enriched toxigenic culture using leftover, deidentified, unformed stool samples from patients suspected of having C. difficile infection.
Nine (9) study sites from geographically diverse locations participated in this study. Nineteen (19) operators distributed across these study sites performed testing with the cobas® Cdiff test. Reference culture (combined direct and enriched toxigenic culture) was performed at a reference laboratory. The remnant sample was stored frozen for discrepant analyses or possible additional testing, as determined by Roche Molecular Solution (RMS).
All evaluable discordant specimens and an equal number of randomly selected and representative concordant samples were used for discrepant testing by an FDA-cleared comparator NAAT. Testing was performed at an external lab that was preselected and qualified by RMS.
Evaluable fresh remnant specimens were prospectively collected from 1,013 patients; 483 males (47.7%) and 530 females (52.3%) with a median age of 59 years (range 5 to 98). All 1,013 specimens had valid results for both combined direct and enrichment culture and the cobas Cdiff test. Of the 1,013 specimens, 179 were positive for toxigenic C. difficile using the combined results from direct and enrichment toxigenic culture, for a prevalence rate of 17.7% for the study.
19
Comparison with Combined Direct and Broth Enrichment Culture 5.3.
The clinical performance of the cobas® Cdiff test compared with the combined results of direct and broth enrichment toxigenic culture are shown in Table 9. The sensitivity and specificity of the cobas® Cdiff test were 87.2% (156/179; 95% CI: 81.5% to 91.3%) and 98.1% (818/834; 95% CI: 96.9% to 98.8%), respectively; and the PPV and NPV were 90.7% (95% CI: 85.4% to 94.2%) and 97.3% (95% CI: 95.9% to 98.2%), respectively. Of the 23 specimens with falsenegative cobas® Cdiff test results relative to combined direct culture and enrichment culture, 19 were negative. 3 were positive and 1 was invalid by the second NAAT method. Of the 16 specimens with false-positive cobas Cdiff test results relative to combined direct and enrichment culture, 14 were positive and 2 were negative by the second NAAT method.
| Table 9: Comparison of cobas Ciat® Cdiff Test with Combine Direct and Enrichment |
|---|
| Culture Results |
| Combined Direct and Enrichment Culture Result | |||
|---|---|---|---|
| cobas® Liat Cdiff Test | |||
| Result | Positive | Negative | Total |
| Detected | 156 | 16 | 172 |
| Not Detected | 23 | 818 | 841 |
| Total | 179 | 834 | 1013 |
| Sensitivity (95% CI) | 87.2% (156/179; 95% CI = 81.5% to 91.3%) | ||
| Specificity (95% CI) | 98.1% (818/834; 95% CI = 96.9% to 98.8%) | ||
| PPV (95% CI) | 90.7% (156/172; 95% CI = 85.4% to 94.2%) | ||
| NPV (95% CI) | 97.3% (818/841; 95% CI = 95.9% to 98.2%) |
Note: Specimens with both combined direct and enrichment culture and valid cobas Liat Cdiff test results are considered evaluable and included in this summary table.
Note: Cl = (score) confidence interval, PPV = positive predictive value, NPV = negative predictive value, OPA = overall percent agreement.
Of the 1,016 specimens tested with the cobas® Cdiff test, 1.4% were initially invalid and 0.2% initially had failed results. Following 1 retest per invalid or failed result, the final invalid rate was 0.1% and the final failed rate was 0%.
20
Comparison with Direct Culture 5.4.
The performance of the cobas® Cdiff test compared to direct culture is shown in Table 10. The positive percent agreement (PPA) and negative percent agreement (NPA) of the cobas® Cdiff test compared to the direct culture for all 1.013 specimens were 94.6% (139/147) and 96.2% (833/866). respectively. Of the 8 specimens with false-negative cobas® Cdiff test results relative to direct culture, 7 were negative and 1 was positive by a second NAAT method. Of the 33 specimens with false-positive cobas 9 Cdiff test results relative to direct culture, only 17 were tested with the second NAAT method: 14 were positive and 3 were negative by that second NAAT method. The remaining 16/33 specimens were positive by enrichment culture and hence not tested with the second NAAT method per the discrepant analysis protocol.
| Table 10: Comparison of cobas Liat® Cdiff Test with Direct Culture Results |
|---|
| Direct Culture Result | |||
|---|---|---|---|
| cobas Liat Cdiff Test Result | Positive | Negative | Total |
| Detected | 139 | 33 | 172 |
| Not Detected | 8 | 833 | 841 |
| Total | 147 | 866 | 1013 |
| PPA | 94.6% (139/147; 95% CI = 89.6% to | ||
| 97.2%) | |||
| NPA | 96.2% (833/866; 95% CI = 94.7% to | ||
| 97.3%) |
Note: Specimens with both direct culture and valid cobas Liat Cdiff test results are considered evaluable and included in this summary table.
Note: CI = (score) confidence interval.
CONCLUSIONS 6.
A comparison of the intended use, technological characteristics, and the results of non-clinical analytical and clinical performance studies demonstrate that the cobas® Cdiff Nucleic acid test for use on the cobas "Liat" System is substantially equivalent to the predicate device.