Clinical and Interpretive

This assay is useful for the sensitive, specific, and rapid diagnosis of Clostridium difficile-associated diarrhea and pseudomembranous colitis.

Clostridium difficile is the cause of Clostridium difficile-associated diarrhea (CDAD), an antibiotic-associated diarrhea, and pseudomembranous colitis (PMC). In these disorders bacterial overgrowth of Clostridium difficile develops in the colon, typically as a consequence of antibiotic usage. Clindamycin and broad-spectrum cephalosporins have been most frequently associated with CDAD and PMC, but almost all antimicrobials may be responsible. Disease is related to production of toxin A and/or B. Treatment typically involves withdrawal of the associated antimicrobials and, if symptoms persist, orally administered and intraluminally active metronidazole, vancomycin, or fidaxomicin. Intravenous metronidazole may be used if an oral agent cannot be administered. In recent years, a more severe form of CDAD with increased morbidity and mortality has been recognized as being caused by an epidemic toxin-hyperproducing strain of Clostridium difficile (NAP1 strain). Many toxin-hyperproducing isolates also contain the binary toxin gene and are resistant quinolones. This test does not differentiate between toxin-hyperproducing and nontoxin-hyperproducing strains.

Traditionally, diagnosis relied upon 1) clinical and epidemiologic features, 2) culture (which is labor intensive and time consuming), 3) cytotoxicity assays, which are labor intensive and time consuming, and 4) toxin detection immunoassays (which are insensitive). The described PCR assay detects the regulatory gene (tcdC) responsible for production of toxins A and B. This test is used for rapid diagnosis of CDAD and PMC enabling prompt treatment that may reduce hospital stays for inpatients with CDAD.

A positive PCR result for the presence of the gene regulating toxin production (tcdC) indicates the presence of Clostridium difficile and toxin A and/or B.

A negative result indicates the absence of detectable Clostridium difficile tcdC DNA in the specimen, but does not rule-out Clostridium difficile infection. False-negative results may occur due to inhibition of PCR, sequence variability underlying the primers or probes, or the presence of Clostridium difficile in quantities less than the limit of detection of the assay.

The assay must be performed on fresh stools, fresh-frozen stools, or stools in transport medium.

The assay is not intended as a test of cure. Since nucleic acid may persist after effective treatment, follow-up testing of a positive result is not recommended.

Interfering substances in the stool may affect the accuracy of the assay; results should always be interpreted in conjunction with clinical and epidemiologic findings.

Submission of more than 1 specimen for testing is not recommended. Patients may asymptomatically carry Clostridium difficile; clinical correlation is needed when deciding how to manage patients with a positive test result.