Used to aid in the diagnosis of Clostridium difficile infection.  Patients should be passing at least 3 unformed (liquid or soft) specimens per 24 hr period.

Results alone are not intended to guide treatment of C. difficile infections.

Colonic colonization with toxogenic strains of C. difficile may lead to active Clostridium difficile infection (CDI).  CDI disease ranges from diarrhea to severe life-threatening pseudomembranous colitis.  The most common risk factor for colonization with C. difficile is exposure to antibiotics.  C. difficle’s primary virulence factor is cytotoxin B.  The pathogenicity locus (PaLoc) includes genes coding for toxin A (tcdA; the enterotoxin) and toxin B (tcdB).  Most pathogenic strains are toxin A-positive and toxin B-positive (A+B+) although toxin A negative, toxin B-positive (A-B+) variant isolates have been recognized as pathogenic.  Some strains of C. difficile also produce an actin-specific ADP-ribosyltransferase called CDT or binary toxin.  The binary toxin locus contains two genes (cdtA and cdtB) and is located outside the PaLoc.
Hypervirulent C. difficile include fluoroquinoline resistant strains belonging to PCR ribotype 027, PFGE type NAP1 and REA type BI (027/NAP1/BI).  They exhibit increased toxin production, which is attributed to deletions in the regulatory gene tcdC.  They are thought to produce more spores, leading to enhanced persistence in the environment, thus epidemiologically significant.
The PCR assay sensitivity is 98.8% and specificity is 90.8% compared to direct culture.  

Repeat testing during the same episode of diarrhea is of limited value (SHEA/IDSA guidelines).  Repeat testing following a negative test during the same episode of diarrhea is not recommended within 7 days of the initial Clostridium difficile assay because of the high sensitivity (99% negative predictive value).  If the patient's signs and symptoms significantly change or if the diarrhea resolved and then recurred in less than 7 days, contact the Clinical Microbiology Laboratory.  “Test-of-cure” is not necessary or required and is a poor predictor of relapse.  Repeat testing at least 14 days after a positive test is appropriate if no clinical resolution of symptoms despite adequate therapy.   Testing asymptomatic patients is also not recommended.

1. Up to 50% of neonates may be colonized with toxigenic Clostridium difficile.  Infectious Diseases consultation recommended.  Performance characteristics were not established by the manufacturer for patients less than 1 years of age.
2. There are many more patients who are asymptomatic carriers of Clostridium difficile (colonized patients) than there are patients with active Clostridium difficile colitis which raises treatment dilemmas for physicians.
3. Inhibition of the assay has been observed in the presence of Zinc oxide paste and Vagisil® cream.
4. Performance of this test has been established using unpreserved, unformed stool specimens only. 
5. Results should be interpreted in conjunction with other laboratory findings and clinical data available to the clinician. Results are not intended to guide treatment of C. difficile infections.

Positive PCR result for the presence of the gene regulating toxin production indicates the presence of Clostridium difficile and toxin A and/or B.
Negative test results indicates the absence of detectable C. difficile DNA but does not rule-out C. difficile infection. 
False negative results may occur from improper specimen collection, not following the recommended sample collection procedure, handling or storage, genomic mutations, or the presence of C difficile in quantities less than the limit of detection of the assay.

Real time PCR qualitative assay that detects the Clostridium difficile toxin B gene (tcd B), the binary toxin gene (CDT), and the single-base-pair deletion at nucleotide 117 within the gene encoding a negative regulator of toxin production (tcd∆117)- not the toxin itself.  Detection of 027/NAP1/BI hypervirulent strains of C. difficile is presumptive and is solely for epidemiological purposes. This assay is FDA approved/cleared. Reflexive action to C. diff Toxin EIA test performed when PCR is positive.

Fresh stool collection in a clean container of unformed (liquid or soft) stool. Store specimens at 2-8º C for no longer than 5 days after collection prior to testing. 
Specimens may be stored at room temperature (20-30º C) for no longer than 24 hours after collection prior to testing.
Specimens submitted to the Clinical Microbiology lab on patients <= 1 year of age will not be performed unless approved by Microbiology Faculty Consult Review.