The Cepheid Xpert® C. difficile/Epi Assay is a qualitative in vitro diagnostic test for rapid detection of toxin B gene sequences and for presumptive identification of 027/NAP1/BI strains of toxigenic Clostridium 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 Cepheid GeneXpert® Dx System 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 Assay is intended as an aid in the diagnosis of CDI. Detection of 027/NAP1/BI strains of C. difficile by the Xpert C. difficile/Epi Assay is presumptive and is solely for epidemiological 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.

Device Description

The Cepheid Xpert C. difficile/Epi Assay is a rapid, automated in vitro diagnostic test for qualitative detection of toxin producing Clostridium difficile directly from unformed (liquid or soft) stool specimens of patients suspected of having Clostridium difficile infection (CDI). The assay detects the toxin B gene (tcdB), the binary toxin gene (CDT), and the single base pair deletion at nucleotide 117 within the gene encoding a negative regulator of toxin production (tcdCA117). The combined presence of the genes encoding toxin B and binary toxin and the tcdCA117 deletion have 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 assay is performed on the Cepheid GeneXpert Dx System. The Xpert C. difficile/Epi Assay system performs sample preparation and real-time, multiplex polymerase chain reaction (PCR) for detection of target-specific DNA. The GeneXpert Dx System consists of a GeneXpert® instrument, personal computer, and disposable fluidic cartridges. Each instrument contains 1-16 randomly accessible modules that are each capable of performing separate sample preparation and real-time PCR tests for detection of C. difficile toxin B and binary toxin gene sequences, and the tcdCA117 deletion, in less than 45 minutes. Each module contains a syringe drive for dispensing fluids, an ultrasonic horn for lysing cells or spores, and I-CORE® thermocycler for performing real-time PCR and detection. A swab is inserted into the stool specimen and then is placed in a tube containing elution reagent. Following brief vortexing, the eluted material and two single-use reagents (Reagent 1 and Reagent 2) that are provided with the Assay are transferred to different, uniquely-labeled chambers of the disposable fluidic cartridge (the Xpert C. difficile/Epi cartridge). The user initiates a test from the system user interface and places the cartridge into the GeneXpert Dx System instrument platform, which performs hands-off real-time, multiplex polymerase chain reaction (PCR) for detection of DNA. In this platform, additional sample preparation, amplification, and real-time detection are all fullyautomated and completely integrated. The Xpert C. difficile/Epi Assay includes reagents for the detection of toxigenic C. difficile and the presumptive detection of sequences found in 027/NAP1/B1 strains. In addition, the assay 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.

AI/ML Overview

Here's a breakdown of the acceptance criteria and the study that proves the device meets them, based on the provided text:

Acceptance Criteria and Device Performance

The acceptance criteria are implied by the performance metrics reported in the clinical comparison study against reference methods. The device's performance is reported relative to these established methods.

Acceptance Criteria (Implied by Reference Method Performance)	Reported Device Performance (Xpert C. difficile/Epi Assay)
Vs. Direct Culture & REA (Toxigenic C. difficile)
Sensitivity	98.72% (232/235)
Specificity	90.86% (1860/2047)
Accuracy	91.67% (2092/2282)
PPV	55.37% (232/419)
NPV	99.84% (1860/1863)
Vs. Direct Culture & REA (BI Strain)
Positive Agreement	98.55% (68/69)
Negative Agreement	97.65% (2161/2213)
Accuracy	97.68% (2229/2282)
PPV	56.67% (68/120)
NPV	99.95% (2161/2162)
Vs. Direct Culture & PFGE (Toxigenic C. difficile)
Sensitivity	98.76% (238/241)
Specificity	90.86% (1860/2047)
Accuracy	91.70% (2098/2288)
PPV	56.00% (238/425)
NPV	99.84% (1860/1863)
Vs. Direct Culture & PFGE (NAP1 Strain)
Positive Agreement	100% (71/71)
Negative Agreement	97.61% (2163/2216)
Accuracy	97.68% (2234/2288)
PPV	57.26% (71/124)
NPV	100% (2164/2164)
Vs. Direct Culture & PCR Ribotyping (Toxigenic C. difficile)
Sensitivity	98.78% (242/245)
Specificity	90.86% (1860/2047)
Accuracy	91.71% (2102/2292)
PPV	56.41% (242/429)
NPV	99.84% (1860/1863)
Vs. Direct Culture & PCR Ribotyping (027 Strain)
Positive Agreement	100% (74/74)
Negative Agreement	97.70% (2167/2218)
Accuracy	97.77% (2241/2292)
PPV	59.20% (74/125)
NPV	100% (2218/2218)
Vs. Reference Culture & REA (Toxigenic C. difficile)
Sensitivity	93.35% (295/316)
Specificity	94.02% (1841/1958)
Accuracy	93.93% (2136/2274)
PPV	71.60% (295/412)
NPV	98.87% (1841/1862)
Vs. Reference Culture & REA (BI Strain)
Positive Agreement	96.51% (83/86)
Negative Agreement	98.31% (2151/2188)
Accuracy	98.24% (2234/2274)
PPV	69.17% (83/120)
NPV	99.86% (2151/2154)
Vs. Reference Culture & PFGE (Toxigenic C. difficile)
Sensitivity	93.60% (307/328)
Specificity	94.02% (1841/1958)
Accuracy	93.96% (2148/2286)
PPV	72.41% (307/424)
NPV	98.87% (1841/1862)
Vs. Reference Culture & PFGE (NAP1 Strain)
Positive Agreement	97.73% (86/88)
Negative Agreement	98.27% (2160/2198)
Accuracy	98.25% (2246/2286)
PPV	69.35% (86/124)
NPV	99.91% (2160/2162)
Vs. Reference Culture & PCR Ribotyping (Toxigenic C. difficile)
Sensitivity	93.39% (311/333)
Specificity	94.02% (1841/1958)
Accuracy	93.93% (2152/2291)
PPV	72.66% (311/428)
NPV	98.82% (1841/1863)
Vs. Reference Culture & PCR Ribotyping (027 Strain)
Positive Agreement	98.89% (89/90)
Negative Agreement	98.36% (2165/2201)
Accuracy	98.38% (2254/2291)
PPV	71.20% (89/125)
NPV	99.95% (2165/2166)

Study Details

Sample size used for the test set and the data provenance:
- Sample Size: 2293 specimens were tested in the overall clinical comparison study.
- Data Provenance: Multi-site prospective investigation study at seven US and Canadian institutions.
Number of experts used to establish the ground truth for the test set and the qualifications of those experts:
- The document does not specify the number or qualifications of experts directly used for ground truth establishment.
- The ground truth methods involved "reference culture followed by cell cytotoxicity testing on the isolates and strain typing on the toxigenic strains by restriction endonuclease analysis (REA), pulsed-field gel electrophoresis (PFGE), and PCR ribotyping methods."
- "Following central culture testing, the toxigenic C. difficile positive isolates were sent to a second set of central laboratories for strain identification by REA, PFGE and PCR ribotyping." This suggests specialized laboratory personnel, but their specific qualifications are not detailed.
Adjudication method for the test set:
- The document does not explicitly describe an adjudication method for conflicting results if multiple experts were involved beyond the described laboratory processes. The ground truth seems to be established through a hierarchical laboratory workflow (initial culture, then cytotoxin B testing, then specific strain typing methods in central labs).
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:
- No, this was not an MRMC study. This device is an automated in vitro diagnostic test (a nucleic acid amplification test), not an imaging-based AI system that assists human readers.
If a standalone (i.e. algorithm only without human-in-the-loop performance) was done:
- Yes, the clinical comparison study evaluates the Xpert C. difficile/Epi Assay as a standalone algorithm. The assay is fully automated, as described: "In this platform, additional sample preparation, amplification, and real-time detection are all fully-automated and completely integrated." Its performance is directly compared against the established reference laboratory methods.
The type of ground truth used (expert consensus, pathology, outcomes data, etc.):
- The ground truth was established through a combination of microbiological culture, cell cytotoxicity testing, and molecular strain typing methods (REA, PFGE, PCR ribotyping) performed in central laboratories. This is a robust laboratory-based ground truth for identifying toxigenic C. difficile and specific hypervirulent strains.
The sample size for the training set:
- The document does not mention a specific training set size. The device is a PCR-based assay, not a machine learning algorithm that typically requires a distinct training set in the same way. The analytical studies (inclusivity, sensitivity, specificity, linearity, interfering substances) would have been used during development and validation, but these don't constitute a "training set" in the machine learning sense.
How the ground truth for the training set was established:
- As no specific "training set" in the machine learning sense is described, there's no mention of how its ground truth would have been established. The analytical studies used well-characterized C. difficile strains and other microorganisms with known genetic profiles (which serves a similar purpose to "ground truth" for analytical validation).

Summary

{0}------------------------------------------------

K110203

5.0 510(k) Summary

As required by 21 CFR Section 807.92(c).

APR - 7 2011

Submitted by:	Cepheid904 Caribbean DriveSunnyvale, CA 90489Phone number: (408) 400-8230Fax number: (408) 541-6439
Contact:	Russel K. Enns, Ph.D.
Date of Preparation:	April 6, 2011
Device:
Trade name:	Xpert® C. difficile/Epi
Common names:	C. difficile/Epi Assay, C. diff/Epi Assay, and Clostridiumdifficile identification and differentiation system
Type of Test:	Qualitative Nucleic Acid Amplification Test for C. difficiletoxin B and binary toxin gene sequences and the single basepair deletion at nucleotide 117 in tcdC from unformed stoolspecimens.
Classification:	I
Classification name:	Device reagents, Clostridium difficile toxin; microorganismdifferentiation and identification device.
Regulation number:	866.2660
Procode:	LLH, OMN
Classification AdvisoryCommittee:	Microbiology
Panel:	83
Predicate Devices:	Cepheid Xpert® C. difficile [510(k) #K001109]BD GeneOhm™ Cdiff Assay [510(k) #K081920]

Device Description:

{1}------------------------------------------------

hypervirulent C. difficile strain known as 027/NAP1/BI, which has been associated with severe disease outbreaks in healthcare facilities worldwide. The assay is performed on the Cepheid GeneXpert Dx System.

The Xpert C. difficile/Epi Assay system performs sample preparation and real-time, multiplex polymerase chain reaction (PCR) for detection of target-specific DNA.

The GeneXpert Dx System consists of a GeneXpert® instrument, personal computer, and disposable fluidic cartridges. Each instrument contains 1-16 randomly accessible modules that are each capable of performing separate sample preparation and real-time PCR tests for detection of C. difficile toxin B and binary toxin gene sequences, and the tcdCA117 deletion, in less than 45 minutes. Each module contains a syringe drive for dispensing fluids, an ultrasonic horn for lysing cells or spores, and I-CORE® thermocycler for performing real-time PCR and detection.

A swab is inserted into the stool specimen and then is placed in a tube containing elution reagent. Following brief vortexing, the eluted material and two single-use reagents (Reagent 1 and Reagent 2) that are provided with the Assay are transferred to different, uniquely-labeled chambers of the disposable fluidic cartridge (the Xpert C. difficile/Epi cartridge). The user initiates a test from the system user interface and places the cartridge into the GeneXpert Dx System instrument platform, which performs hands-off real-time, multiplex polymerase chain reaction (PCR) for detection of DNA. In this platform, additional sample preparation, amplification, and real-time detection are all fullyautomated and completely integrated.

The Xpert C. difficile/Epi Assay includes reagents for the detection of toxigenic C. difficile and the presumptive detection of sequences found in 027/NAP1/B1 strains. In addition, the assay 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.

Device Intended Use:

The Cepheid Xpert® C. difficile/Epi Assay is a qualitative in vitro diagnostic test for rapid detection of toxin B gene sequences and for presumptive identification of 027/NAP1/BI strains of toxigenic Clostridium 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 tedC gene. The tcdC gene encodes for a negative regulator in C. difficile toxin production. The test is performed on the Cepheid GeneXpert® Dx System 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 Assay is intended

{2}------------------------------------------------

as an aid in the diagnosis of CDI. Detection of 027/NAP1/BI strains of C. difficile by the Xpert C. difficile/Epi Assay is presumptive and is solely for epidemiological 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.

Substantial Equivalence:

The Xpert C. difficile/Epi Assay is substantially equivalent to the Cepheid Xpert C. difficile Assay and the BD Diagnostics GeneOhm Cdiff Assay. All three assays qualitatively detect C. difficile toxin B gene (tcdB) in unformed (liquid or soft) stool specimens and use real-time PCR amplification and fluorogenic target-specific hybridization detection.

Table 5.1 shows the similarities and differences between the Xpert C. difficile/Epi Assay and the predicate devices.

The Xpert C. difficile/Epi is also substantially equivalent to the C. difficile reference culture method followed with strain identification of all C. difficile isolates as shown in a multi-center clinical comparison study.

The multi-center clinical comparison study was conducted on 2293 patients to evaluate the performance of the Xpert C. difficile Assay relative to the reference culture method and cytotoxin B isolate testing. Following culture testing, the toxigenic C. difficile isolates were sent to three central laboratories for strain typing by PCR Ribotyping, PFGE and REA methods for the identification of 027/NAP1/BI hypervirulent strains.

The test results showed the Xpert C. difficile Assay to be substantially equivalent to the current standard of care, the C. difficile reference culture method followed with strain identification of all toxigenic C. difficile isolates.

{3}------------------------------------------------

	Device	Predicate	Predicate
	Xpert C. difficile/Epi Assay	Xpert C. difficileAssay (K091109)	BD GeneOhmCdiff Assay(K081920)
IntendedUse	The Cepheid Xpert® C.difficile/Epi Assay is a qualitativein vitro diagnostic test for rapiddetection of toxin B genesequences and for presumptiveidentification of 027/NAP1/BIstrains of toxigenic Clostridiumdifficile from unformed (liquid orsoft) stool specimens collectedfrom patients suspected of havingC. difficile infection (CDI).Presumptive identification of027/NAP1/BI strains of C. difficileis by detection of binary toxin(CDT) gene sequences and thesingle base pair deletion atnucleotide 117 in the tcdC gene.The tcdC gene encodes for anegative regulator in C. difficiletoxin production. The test isperformed on the CepheidGeneXpert® Dx System andutilizes automated real-timepolymerase chain reaction (PCR)to detect toxin gene sequencesassociated with toxin producing C.difficile . The Xpert C. difficile/EpiAssay is intended as an aid in thediagnosis of CDI. Detection of027/NAP1/BI strains of C. difficileby the Xpert C. difficile/Epi Assayis presumptive and is solely forepidemiological purposes and isnot intended to guide or monitortreatment for C. difficileinfections. Concomitant culture isnecessary only if further typing ororganism recovery is required.	The Cepheid Xpert C.difficile Assay,performed on theCepheid GeneXpert®Dx System, is aqualitative in vitrodiagnostic test forrapid detection oftoxin B genesequences fromunformed (liquid orsoft) stool specimenscollected frompatients suspected ofhaving Clostridiumdifficile infection(CDI). The testutilizes automatedreal-time polymerasechain reaction (PCR)to detect toxin genesequences associatedwith toxin producingC. difficile . The XpertC. difficile Assay isintended as an aid inthe diagnosis of CDI.Concomitant cultureis necessary only iffurther typing ororganism recovery isrequired.	The BD GeneOhmCdiff Assay is arapid in vitrodiagnostic test forthe direct,qualitativedetection of C.difficile toxin Bgene ( tcdB ) inhuman liquid orsoft stoolspecimens frompatients suspectedof havingClostridiumdifficile -associateddisease (CDAD).The test, based onreal-time PCR, isintended for use asan aid in diagnosisof CDAD. The testis performeddirectly on thespecimen, utilizingpolymerase chainreaction (PCR) forthe amplification ofspecific targets andfluorogenic target-specifichybridizationprobes for thedetection of theamplified DNA.
	Device	Predicate	Predicate
Item	Xpert C. difficile/Epi Assay	Xpert C. difficileAssay (K091109)	BD GeneOhmCdiff Assay(K081920)
Indicationfor Use	Identification of C. difficile frompatients suspected of having C.difficile Infection (CDI).	Same	Same
Techno-logicalPrinciples	Fully-automated nucleic acidamplification (DNA); real-timePCR	Same	Same
SpecimenType	Unformed (liquid or soft) Stool	Same	Same
TestCartridge	Disposable single-use, multi-chambered fluidic cartridge.	Same as Xpert C.difficile/Epi Assay	Disposable single-use PCR tube
DNATargetSequences	C. difficile toxin B, binary toxinand the tcdC deletion nt 117(tcdCA117)	C. difficile toxin Bonly	C. difficile toxin Bonly
InstrumentSystem	Cepheid GeneXpert Dx System	Same as Xpert C.difficile/Epi Assay	CepheidSmartCycler DxSystem
SampleExtraction	Self-contained and automated afterswab elution and two single-dosereagent additions.	Same as Xpert C.difficile/Epi Assay	Manual
Probes	TaqMan® Probes	Same as Xpert C.difficile/Epi Assay	Molecular Beacons
SampleExtraction	Automated	Same as Xpert C.difficile/Epi Assay	Manual
Rapid testresults	Less than 45 minutes to results.	Same as Xpert C.difficile/Epi Assay	Approximately 75-90 minutes toresults.
Users	Operators with no clinical labexperience to experienced clinicallaboratory technologists.	Same/ CLIAModerate ComplexityLaboratory Users	CLIA HighComplexityLaboratory Users

Table 5.1: Similarities and Differences Between the Xpert C. difficile/Epi Assay and the Predicate Devices

{4}------------------------------------------------

{5}------------------------------------------------

Non-Clinical Studies:

Analytical Inclusivity

The analytical inclusivity of the Xpert C. difficile/Epi Assay was determined using 13 Clostridium difficile strains of different toxinotypes selected to represent the range of genetic diversity found in C. difficile. Toxinotypes 0, I, III. IV, V, VI, VIII, IX, X, XII, XIV, XXI, and XXII were tested. All strains were tested in triplicate with 900 CFU/swab. All tested toxinotypes were correctly reported as Toxigenic C. difficile positive. In addition, all strains were reported either as 027/NAP1/BI presumptive negative or presumptive positive. In three toxinotypes X, IV and XIV, one to three replicates were incorrectly reported as 027/NAP1/BI presumptive positive, respectively. All other strains were correctly identified as 027/NAP1/BI presumptive positive or negative.

Analytical Sensitivity (Limit of Detection)

Studies were performed to determine the 95% confidence intervals for the analytical limit of detection (LoD) of C. difficile diluted into a fecal matrix of human origin that can be detected by the Xpert C. difficile/Epi Assay. The fecal matrix consisted of human liquid feces (C. difficile negative by Xpert C. difficile/Epi Assay) diluted in PBS with 15% glycerol. The LoD is defined as the lowest number of colony forming units (CFU) per swab that can be reproducibly distinguished from negative samples with 95% confidence.

Replicates of 20 were evaluated at each C. difficile concentration tested (CFU/swab) for 7 different C. difficile strains representing toxinotypes 0 (two strains), III (two strains), IV, V and VIII (one of each strain).

The estimate and confidence intervals were determined using logistic regression with data (number of positive results per number of replicates at each level) over the range of CFU loadings. The confidence intervals were determined using maximum likelihood estimates on the logistic model parameters using the large sample variance-covariance matrix. The LoD point estimates and 95% upper and lower confidence intervals for each C. difficile toxinotype tested are summarized in Table 5.2.

{6}------------------------------------------------

Strain ID	Toxinotype	LoD95%(CFU/swab)	Lower95% CI	Upper95% CI
VPI 10463 (CCUG19126)	0	255	190	632
90556-M6S (ATCC9689)	0	460	419	587
LUMC-1 (027/NAP1/BI)	III	23	19	31
LUMC-5 (027/NAP1/BI)	III	75	45	176
LUMC-7	V	45	34	104
LUMC-6	VIII	60	50	74
9101	XII	41	34	49

	Table 5.2: 95% Confidence Intervals for Analytical LoD – C. difficile
--	------------------------------------------------------------------------------	--

The results of this study indicate that the Xpert C, difficile/Epi Assay will produce a positive C. difficile result 95% of the time for a fecal sample containing 460 CFU/swab and a presumptive positive 027/NAP1/BI result 95% of the time for a swab containing 75 CFU.

In addition to the LoD determination, eighteen C. difficile strains representing toxinotypes 0 plus 12 variant toxinotypes, including four 027/NAP1/BI toxinotype III isolates, were tested using the Xpert C. difficile/Epi Assay. C. difficile strains were selected to broadly represent the majority of C. difficile toxinotypes encountered in practice. Stock cultures were prepared by suspending the bacterial growth from agar plates in PBS buffer containing 15% glycerol. The concentration of each stock was adjusted to 1.4-5.9 McFarland units. All strains were serially diluted to approximately 900 CFU/swab and tested in triplicate.

Under the conditions of this study, the Xpert C. difficile/Epi Assay correctly identified all 18 strains tested as "Toxigenic C. diff POSITIVE". Included in the panel were 8 toxinotypes reported to be positive for binary toxin (CDT) production as well. All were CDT positive using the Xpert C. difficile/Epi Assay. All four 027/NAP1/BI isolates representing toxinotype III were correctly identified as "Toxigenic C. diff POSITIVE; 027-NAP1-BI PRESUMPTIVE POSITIVE".

Linearity

A study was conducted to define the reportable range of the Xpert C. difficile/Epi Assay and demonstrated a linear relationship.

Analytical Specificity

Fifty-five (55) strains were collected, quantitated and tested using the Xpert C. difficile/Epi Assay. The strains originated from the American Type Culture Collection (ATCC), Culture Collection University of Göteborg (CCUG), German Collection of Microorganisms and Cell Cultures (DSMZ), the Centers for Disease Control and Prevention (CDC), the Institute of Public Health, Maribor, Slovenia and Swedish Institute for Infectious Disease Control (SMI).

{7}------------------------------------------------

Of the tested species, ten (10) non-toxigenic C. difficile strains and eleven (11) non C. difficile Clostridium species were included. The organisms tested were identified as either Gram positive (37) or Gram negative (18). The organisms were further classified as aerobic (24), anaerobic (29) or microaerophilic (2).

Each strain was tested in triplicate at concentrations ranging from 1.1x108 to 2.2x1000 Positive and negative controls were included in the study. Under the conditions of the study, all isolates were reported "Toxigenic C. diff NEGATIVE; 027/NAP1/BI PRESUMPTIVE NEG". The analytical specificity was 100%.

Interfering Substances

Twenty-one (21) biological and chemical substances occasionally used or found in stool specimens were tested for interference with the Xpert C. difficile/Epi Assay. Potentially interfering substances include, but are not limited to, Vagisil cream and zinc oxide paste. The 19 substances listed in Table 5.3 showed no detectable interference with the Xpert C. difficile/Epi Assay.

Substance	Substance
Whole Blood	K-Y Jelly/Gelée®
Karolinska University Hospital	McNeil-PPC
Mucin (porcine)	Vaseline
Sigma	Unilever
Kaopectate®	Dulcolax®
Chattem	Boehringer Ingelheim Pharmaceuticals
Imodium®	Preparation H Portable Wipes
McNeil-PPC	Wyeth Consumer Healthcare
Pepto-Bismol®	Vaginal Contraceptive Film (VCF)
Procter & Gamble	Apothecus Pharmaceutical
Preparation H®	Vancomycin
Wyeth Consumer Healthcare	Fluka
Fleet®	Metronidazole
CB Fleet Company	Actavis
Fecal fats	Anusol® Plus
Karolinska University Hospital	TM Warner-Lambert Company
Monistat®	E-Z-HD™ High Density Barium Sulfatefor suspension
McNeil-PPC	E-Z-EM Canada
Hydrocortisone Cream
Longs Drugs

Table 5.3: Substances Tested and Showing No Assay Interference

{8}------------------------------------------------

Clinical Studies

Clinical Comparison Study

Performance characteristics of the Xpert C. difficile/Epi Assay were determined in a multi-site prospective investigation study at seven US and Canadian institutions by comparing the Xpert C. difficile/Epi Assay to reference culture followed by cell cytotoxicity testing on the isolates and strain typing on the toxigenic strains by restriction endonuclease analysis (REA), pulsed-field gel electrophoresis (PFGE), and PCR ribotyping methods.

Subjects included individuals whose routine care called for C. difficile testing. A portion of each leftover unformed stool specimen was obtained for testing by the Xpert C. difficile/Epi Assay. The remaining excess specimen was sent to a central laboratory for reference culture and cytotoxin B isolate testing, Each stool specimen was inoculated onto pre-reduced CCFA-D (cycloserine-cefoxitin-fructose agar -direct plate) and Cycloserine cefoxitin mannitol broth with taurocholate lysozyme cysteine (CCMB-TAL). After 24 hours the CCMB-TAL was subcultured on to a second CCFA-E plate (CCFA-Enriched). This direct-enriched culture method is referred to hereafter as "reference culture".

If C. difficile was isolated from the CCFA-D plate and the isolate was positive by cell cytotoxicity assay, the specimen was classified as "toxigenic C. difficile positive" and CCFA-E plate was not further analyzed. If no C. difficile was isolated from the CCFA-D plate or if the isolate was negative by cell cytotoxicity assay, the CCFA-E plate was further analyzed.

If CCFA-E was positive for C. difficile and the isolate was positive for cell cytotoxicity assay, the specimen was classified as "toxigenic C. difficile positive". The specimen was reported as "negative" if CCFA-E was negative for C. difficile or the isolate was tested negative by cell cytotoxicity assay.

Following central culture testing, the toxigenic C. difficile positive isolates were sent to a second set of central laboratories for strain identification by REA, PFGE and PCR ribotyping.

Performance of the Xpert C. difficile/Epi Assay was calculated relative to the results of direct culture with strain typing, for each of the three strain typing methods, and reference culture with strain typing, for each of the three strain typing methods.

{9}------------------------------------------------

Overall Results

A total of 2293 specimens were tested by Xpert C. difficile/Epi Assay, culture, and strain typing.

Performance vs. Direct Culture

Relative to direct culture with REA strain typing, the Xpert C. difficile/Epi Assay demonstrated a sensitivity and specificity for toxigenic C. difficile of 98.72% and 90.86%, respectively. The Xpert C. difficile/Epi Assay also demonstrated 98.55% positive agreement and 97.65% negative agreement for BI (Table 5.4).

	Direct Culture & REA
Xpert C. diff/Epia	Toxin B +BI +	Toxin B +BI –	NEG	Totalb
Toxin B +027/NAP1/BI +	68	5	47	120
Toxin B +027/NAP1/BI–	1	158	140	299
NEG	0	3	1860	1863
Total	69	166	2047	2282
		Toxigenic C. difficile		Toxigenic C. difficile / 027/NAP1/BI
		Sensitivity:	98.72% (232/235)	Pos Agreement: 98.55% (68/69)
		Specificity:	90.86% (1860/2047)	Neg Agreement: 97.65% (2161/2213)
		Accuracy:	91.67% (2092/2282)	Accuracy: 97.68% (2229/2282)
		PPVc:	55.37% (232/419)	PPV: 56.67% (68/120)
		NPVd:	99.84% (1860/1863)	NPV: 99.95% (2161/2162)

Table 5.4: Xpert C. difficile/Epi Assay Performance vs. Direct Culture & REA

a Xpert results shown are for first or second attempt. Approximately 3.2% of the specimens were indeterminate on the first attempt.

6 11 specimens were culture positive but were not strain typed for the following reasons: incomplete restriction endonuclease digestion; or the isolate was not sent. These 11 specimens are not included in the performance characteristics above.

6 Positive predictive value

d Negative predictive value

{10}------------------------------------------------

Relative to direct culture with PFGE strain typing, the Xpert C. difficile/Epi Assay demonstrated a sensitivity and specificity for toxigenic C. difficile of 98.76% and 90.86%, respectively. The Xpert C. difficile/Epi Assay also demonstrated 100% positive agreement and 97.61% negative agreement for NAP1 (Table 5.5).

	Direct Culture & PFGE
	Toxin B +NAP1 +	Toxin B +NAP1 -	NEG	Totalb
Xpert C. diff/Epia	Toxin B +;027/NAP1/BI +	71	6	47	124
	Toxin B +;027/NAP1/BI-	0	161	140	301
	NEG	0	3	1860	1863
	Total	71	169	2047	2288
	Toxigenic C. difficile		Toxigenic C. difficile / 027/NAP1/BI
	Sensitivity:Specificity:Accuracy:PPVc:	98.76% (238/241)90.86% (1860/2047)91.70% (2098/2288)56.00% (238/425)	Pos Agreement:Neg Agreement:Accuracy:PPV:	100% (71/71)97.61% (2163/2216)97.68% (2234/2288)57.26% (71/124)

Table 5.5: Xpert C. difficile/Epi Assav Performance vs. Direct Culture & PFGE

4 Xpert results shown are for first or second attempt. Approximately 3.2% of the specimens were indeterminate on the first attempt.

99.84% (1860/1863)

6 5 specimens were culture positive but were not strain typed for the following reasons: incomplete restriction endomuclease digestion: no growth; or contamination. These 5 specimens are not included in the performance characteristics above.

NPV:

·Positive predictive value

NPV4:

dNegative predictive value

100% (2164/2164)

{11}------------------------------------------------

Relative to direct culture with PCR ribotyping, the Xpert C. difficile/Epi Assay demonstrated a sensitivity and specificity for toxigenic C. difficile of 98.78% and 90.86%, respectively. The Xpert C. difficile/Epi Assay also demonstrated 100% positive agreement and 97.70% negative agreement for 027 (Table 5.6).

			Table 5.6: Xpert C. difficile/Epi Assay Performance vs. Direct Culture &
Compression, consisted consistent comes and to control and charges and charges and charges and charges and charges and charges and charges and charges and charges and constru		PCR Ribotyping

	Direct Culture & PCR-Ribotyping
Xpert C. diff/Epia		Toxin B +027+	Toxin B +027 -	NEG	Totalb
	Toxin B +;027/NAP1/BI +	74	4	47	125
	Toxin B +;027/NAP1/BI -	0	164	140	304
	NEG	0	3	1860	1863
	Total	74	171	2047	2292
		Toxigenic C. difficile		Toxigenic C. difficile / 027/NAP1/BI
		Sensitivity: 98.78% (242/245)		Pos Agreement: 100% (74/74)
		Specificity: 90.86% (1860/2047)		Neg Agreement: 97.70% (2167/2218)
		Accuracy: 91.71% (2102/2292)		Accuracy: 97.77% (2241/2292)
		PPVc: 56.41% (242/429)		PPV: 59.20% (74/125)
		NPVd: 99.84% (1860/1863)		NPV: 100% (2218/2218)

4 Xpert results shown are for first or second attempt. Approximately 3.2% of the specimens were indeterminate on the first attempt.

One isolate was not typeable due to contamination; this specimen is not included in the performance statistics.

"Positive predictive value

ªNegative predictive value

{12}------------------------------------------------

Performance vs. Reference Culture

Reference (enriched) culture is a more sensitive method for detection of C. difficile in symptomatic patients, for example it allows detection of low number of organism due to prior antibiotic treatment and potential loss of viability due to specimen transport.

Relative to reference culture with REA strain typing, the Xpert C. difficile/Epi Assay demonstrated a sensitivity and specificity for toxigenic C. difficile of 93.35% and 94.02%, respectively. The Xpert C. difficile/Epi Assay also demonstrated 96.51% positive agreement and 98.31% negative agreement for BI (Table 5.7).

	Reference Culture & REA
	Toxin B +BI +	Toxin B +BI -	NEG	Totalb
Xpert C. diff/Epra	Toxin B +;027/NAP1/BI +	83	6	31	120
	Toxin B +;027/NAP1/BI -	2	204	86	292
	NEG	1	20	1841	1862
	Total	86	230	1958	2274
		Toxigenic C. difficile		Toxigenic C. difficile / 027/NAP1/BI
		Sensitivity:	93.35% (295/316)	Pos Agreement:	96.51% (83/86)
		Specificity:	94.02% (1841/1958)	Neg Agreement:	98.31% (2151/2188)
		Accuracy:	93.93% (2136/2274)	Accuracy:	98.24% (2234/2274)
		PPVc:	71.60% (295/412)	PPV:	69.17% (83/120)
		NPVd:	98.87% (1841/1862)	NPV:	99.86% (2151/2154)

Table 5.7: Xpert C. difficile/Epi Assay Performance vs. Reference Culture & REA

4 Xpert results shown are for first or second attempt. Approximately 3.3% of the specimens were indeterminate on the first attempt.

b 19 specimens were culture positive but were not strain typed for the following reasons: incomplete restriction endonuclease digestion; or the isolate was not sent. These 19 specimens are not included in the performance characteristics above.

Positive predictive value

dNegative predictive value

{13}------------------------------------------------

Relative to reference culture with PFGE strain typing, the Xpert C. difficile/Epi Assay demonstrated a sensitivity and specificity for toxigenic C. difficile of 93.60% and 94.02%, respectively. The Xpert C. difficile/Epi Assay also demonstrated 97.73% positive agreement and 98.27% negative agreement for NAP1 (Table 5.8).

	Reference Culture & PFGE
		Toxin B +NAP1 +	Toxin B +-NAP1 -	NEG	Totalb
Xpert C. diff/Epia	Toxin B +;027/NAP1/BI +	86	7	31	124
	Toxin B +;027/NAP1/BI -	1	213	86	300
	NEG	1	20	1841	1862
	Total	88	240	1958	2286
		Toxigenic C. difficile		Toxigenic C. difficile / 027/NAP1/BI
		Sensitivity:	93.60% (307/328)	Pos Agreement:	97.73% (86/88)
		Specificity:	94.02% (1841/1958)	Neg Agreement:	98.27% (2160/2198)
		Accuracy:	93.96% (2148/2286)	Accuracy:	98.25% (2246/2286)
		PPVc:	72.41% (307/424)	PPV:	69.35% (86/124)
		NPVd:	98.87% (1841/1862)	NPV:	99.91% (2160/2162)

Table 5.8: Xpert C. difficile/Epi Assay Performance vs. Reference Culture & PFGE

4 Xpert results shown are for first or second attempt. Approximately 3.2% of the specimens were indeterminate on the first attempt.

6 7 specimens were culture positive but were not strain typed for the following reasons: incomplete restriction endomiclease digestion; no growth; or contamination. These 11 specimens are not included in the performance characteristics above.

°Positive predictive value

"Negative predictive value

{14}------------------------------------------------

Relative to reference culture with PCR ribotyping, the Xpert C. difficile Assay demonstrated a sensitivity and specificity for toxigenic C. difficile of 93.39% and 94.02%, respectively. The Xpert C. difficile Assay also demonstrated 98.89% positive agreement and 98.36% negative agreement for 027 (Table 5.9).

Ribotyping
	Reference Culture & PCR-Ribotyping
Xpert C. diff/Epia		Toxin B +027+	Toxin B +027 –	NEG	Totalb
	Toxin B +;027/NAP1/BI +	89	5	31	125
	Toxin B +;027/NAP1/BI -	0	217	86	303
	NEG	1	21	1841	1863
	Total	90	243	1958	2291
		Toxigenic C. difficile		Toxigenic C. difficile / 027/NAP1/BI
		Sensitivity:	93.39% (311/333)	Pos Agreement:	98.89% (89/90)
		Specificity:	94.02% (1841/1958)	Neg Agreement:	98.36% (2165/2201)
		Accuracy:	93.93% (2152/2291)	Accuracy:	98.38% (2254/2291)
		PPVc:	72.66% (311/428)	PPV:	71.20% (89/125)
		NPVd:	98.82% (1841/1863)	NPV:	99.95% (2165/2166)

		Table 5.9: Xpert C. difficile Assay Performance vs. Reference Culture & PCR-
	Ribotyping

4 Xpert results shown are for first or second attempt. Approximately 3.2% of the specimens were indeterminate on the first attempt.

6 2 specimens were culture positive but were not strain typeable due to contamination and are not included in the performance characteristics above.

Positive predictive value

·Negative predictive value

Antibiotic Usage

Among the 2293 cases included in the main dataset, antibiotic use within the 2 months prior to sample collection was reported for 1630 and no antibiotic use was confirmed for 570; for 93 cases, antibiotic status was unknown. Antibiotic use did not cause a statistically significant difference in assay performance.

{15}------------------------------------------------

Reproducibility

Reproducibility of the Xpert C. difficile/Epi Assay was demonstrated using a panel of 7 specimens with varying concentrations of a toxigenic C. difficile strain, a toxigenic C. difficile 027/NAP1/BI strain and a negative that were tested in duplicate on 10 different days at each of the three sites (7 specimens x 2 times/ day x 10 days x 3 sites). One lot of Xpert C. difficile kit was used at each of the 3 testing sites. Xpert C. difficile/Epi Assays were performed according to the Xpert C. difficile/Epi procedure.

A panel of 7 specimens with varying concentrations of C. difficile and C. difficile. 027/NAP1/BI were tested on 10 different days by two different operators at each of the three sites (7 specimens x 2 operators/ day x 10 days x 3 sites). One lot of Xpert C. difficile/Epi Assay was used at each of the 3 testing sites. Xpert C. difficile/Epi Assays were performed according to the Xpert C. difficile/Epi Assay procedure. Results are summarized in Table 5.10.

Specimen ID	Site 1	Site 2	Site 3	% TotalAgreement bySample
Negative	100%(20/20)	100%(20/20)	100%(20/20)	100%(60/60)
Toxigenic C. difficile High Negative	100%(20/20)	100%(20/20)	100%(20/20)	100%(60/60)
Toxigenic C. difficile Low Positive	100%(20/20)	85%(17/20)	85%(17/20)	90.0%(54/60)
Toxigenic C. difficile ModeratePositive	100%(20/20)	100%(20/20)	100%(20/20)	100%(60/60)
027/NAP1/BI High Negative	100%(20/20)	100%(20/20)	100%(20/20)	100%(60/60)
027/NAP1/BI Low Positive	100%(20/20)	95%(19/20)	95%(19/20)	96.7%(58/60)
027/NAP1/BI Moderate Positive	100%(20/20)	100%(20/20)	100%(20/20)	100%(60/60)
% Total Agreement by Site	100%(140/140)	97.1%(136/140)	97.1%(136/140)	98.1%(412/420)

Table 5.20: Summary of Reproducibility Results (all)

Conclusions

The results of the nonclinical and clinical performance studies summarized above demonstrate that the Xpert C. difficile/Epi Assay is as safe, as effective, and performs as well as or better than the predicate devices.

{16}------------------------------------------------

Image /page/16/Picture/0 description: The image shows the logo for the Department of Health & Human Services (HHS) in the USA. The logo features a stylized depiction of an eagle or bird with three curved lines forming its body and wings. The text "DEPARTMENT OF HEALTH & HUMAN SERVICES - USA" is arranged in a circular pattern around the bird symbol.

DEPARTMENT OF HEALTH & HUMAN SERVICES

Public Health Service

Food and Drug Administration 10903 New Hampshire Avenue Silver Spring, MD 20993

Cepheid c/o Russel K. Enns. Ph.D. Senior Vice President, Chief Regulatory Officer 904 Caribbean Drive Sunnyvale. CA 94089-1189

APR 0 7 2011

Re: K110203

Trade/Device Name: Regulation Number: Regulation Name: Regulatory Class: Product Code: Dated: Received:

Xpert® C. difficile/Epi 21 CFR 8866.2660 Microorganism differentiation and identification device Class I OMN January 21, 2011 January 24, 2011

Dear Dr. Enns:

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, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration.

If your device is classified (see above) into class II (Special Controls), it may be subject to such additional controls. Existing major regulations affecting your device can be found in Title 21, Code of Federal Regulations (CFR), Parts 800 to 895. 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 Parts 801 and 809); medical device reporting (reporting of medical device-related adverse events) (21 CFR 803); and good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820). This letter will allow you to begin marketing your device as described in your Section 510(k) premarket notification. The FDA finding of substantial equivalence of your device to a legally marketed predicate device results in a classification for your device and thus, permits your device to

{17}------------------------------------------------

Page 2 - Russel K. Enns, Ph.D.

proceed to the market.

If you desire specific advice for your device on our labeling regulation (21 CFR Parts 801 and 809), please contact the Office of In Vitro Diagnostic Device Evaluation and Safety at (301) 796-5450. 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 Small Manufacturers, International and Consumer Assistance at its toll-free number (800) 638-2041 or (301) 796-7100 or at its Internet address http://www.fda.gov/cdrl/industry/support/index.html.

Sincerely yours.

Saliaotypica

Sally A. Hojvat, M.Sc., Ph Director Division of Microbiology Devices Office of In Vitro Diagnostic Device Evaluation and Safety Center for Devices and Radiological Health

Enclosure

{18}------------------------------------------------

4.0 Indications for Use Form

510(k) Number (if known): K110203

Device Name: Xpert® C. difficile/Epi Assay

Indications for Use:

The Cepheid Xpert® C. difficile/Epi Assay is a qualitative in vitro diagnostic test for rapid detection of toxin B gene sequences and for presumptive identification of 027/NAP1/BI strains of toxigenic Clostridium 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 tedC gene. The tcdC gene encodes for a negative regulator in C. difficile toxin production. The test is performed on the Cepheid GeneXpert® Dx System 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 Assay is intended as an aid in the diagnosis of CDI. Detection of 027/NAP 1/BI strains of C. difficile by the Xpert C. difficile/Epi Assay is presumptive and is solely for epidemiological 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.

Prescription Use X	AND/OR Over-The-Counter Use _
(Part 21 CFR 801 Subpart D)	(21 CFR 801 Subpart C)

(PLEASE DO NOT WRITE BELOW THIS LINE-CONTINUE ON ANOTHER PAGE OF NEEDED)

Concurrence of CDRH, Office of In Vitro Diagnostic Devices (OIVD)

Freddie W. Cooke

Division Sign-Off Office of In Vitro Diagnostic Device Evaluation and Safety

510(k) K110203

Page 1 of 1

Regulation Number and Section

§ 866.2660 Microorganism differentiation and identification device.

(a)
Identification. A microorganism differentiation and identification device is a device intended for medical purposes that consists of one or more components, such as differential culture media, biochemical reagents, and paper discs or paper strips impregnated with test reagents, that are usually contained in individual compartments and used to differentiate and identify selected microorganisms. The device aids in the diagnosis of disease.(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 § 866.9.