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					                          DSM      Micro Notes      CLINICAL MICROBIOLOGY DISCIPLINE PUBLICATION
                                                                       DIAGNOSTIC SERVICES OF MANITOBA
                                                                                   February 11, 2010

                              Clostridium difficile Laboratory Testing*
                                             The Scoop on Poop: Key Questions and Answers
                                                    Prepared by: Dr. Heather Adam and Dr. Michelle Alfa, DSM

      *Note: this information pertains only to specimens sent to DSM laboratories and may differ from testing performed at Cadham Provincial Laboratory

Why             }     C. difficile-Associated Diarrhea (CDAD)/
                      C. difficile Infections (CDI)                                              Who      }       Patients at Increased Risk

                            C. difficile is an opportunistic, gram-                               •   Current or recent receipt of antimicrobial therapy
                            positive, spore-forming bacillus. Upon                                •   Age > 65 years
                            disruption of the normal fecal flora, by                              •   Hospitalization
                            antimicrobial use or other mechanisms and                             •   Severe underlying illness
                            exposure to C. difficile, toxin-producing
                            strains of this organism can cause
                            diarrhea. C. difficile spores can be spread
                            by stool contamination of the environment
                            as well as gloved and ungloved hands.
                                                                                                 What     }       Specimen Collection & Rejection Criteria

     C.difficile colonies                                                                        Correct Specimen:
                            Ingestion of spores can result in a C.
                            difficile infection.                                                  • ≥ 5 mL of liquid stool in a sterile, leak-proof screw capped
CDAD is the most common cause of infectious nosocomial diarrhea.                                     container
In 2008, there were 890 cases of C. difficile infections reported in
Manitoba (                              Inappropriate Specimens:
html). The number of reported C. difficile infections is 1.5 – 2 times                             • Samples of insufficient volume (< 3 mL)
greater than the number of reported                                                                • Formed stools (unless there is a diagnosis of toxic megacolon)
infections due to the other enteric                                                                • Samples on infants < one year of age
pathogens combined (Salmonella,                                                                    • > three samples on one patient
Shigella, Campylobacter, E. coli 0157:H7,

                                                                                                          }       Laboratory Testing
and Yersinia) (Figure 1).
Range of clinical manifestations:                                                                When             (available at DSM’s Health Sciences Centre, St. Boniface
asymptomatic colonization – mild to                                                                               Hospital, Westman Lab, and Thompson sites)
severe diarrhea – pseudomembranous            C.difficile with spores
colitis – toxic megacolon – death.                                                               The laboratory will process up to three consecutive negative stools
                                                                                                 from one patient (no more than one per day). Ideally, a second (or
                                                                                                 third) sample should not be submitted until the results of the previous
Figure 1. Number of cases of enteric pathogen infections reported in                             test(s) are received.
Manitoba in 2009 (Jan – Aug 2009)
 C. difficile     Campylobacter    Salmonella    Shigella   Yersinia   E. coli O157:H7           Once a positive result is reported, additional samples should not
                                                                                                 be submitted for at least seven days. ‘Test of cure’ samples are not
   C. difficile     Campylobacter      Salmonella    Shigella    Yersinia    E. coli O157:H7     useful and may be misleading as patients may excrete toxin for weeks
                                                                                                 following therapy despite good clinical response.
                                   3   28
                             16                                                                  The recommended volume of liquid or soft stool to perform the
        171                                                                                      standard C. difficile toxin testing algorithm is ≥ 5 mL. Low volume
                                       3    28                                                   specimens (< 3 mL) will not be processed.

                                                                                                 How           Testing Algorithms for Toxigenic C. difficile

                                                                                                 Figures 2 and 3 are the algorithms used in DSM Clinical Microbiology
                                                                                                 Laboratories to test stool specimens for toxigenic C. difficile. Recent
151                                                                                  561
                                                                                                 published data1 supports the DSM algorithms as the most sensitive
                                                                                                 and specific testing for toxigenic C. difficile.
 151                                                                                       561
Micro Notes                    DIAGNOSTIC SERVICES OF MANITOBA                                                                       February 11, 2010

Figure 2. C. difficile testing algorithm for up to two stools submitted from one patient

                                                                                                    GD antigen: Glutamate dehydrogenase
                                                                                                     – detects presence of C. difficile (not the
                                                                                                     production of toxins)
                                                                                                    Toxin A & B antigen test: Detects C.
                                                                                                    difficile toxins A & B
                                                                                                    CPE test: Cell cytotoxin assay detects toxin-
                                                                                                    producing C. difficile
                                                                                                    *Positive stool samples are frozen for ~ three

Figure 3. C. difficile testing algorithm for the third stool submitted from a patient with previously negative C. difficile toxin tests or low volume

                                                                                                {       Alcohol shock: Selects C. difficile by
                                                                                                        eliminating non-spore forming fecal flora
                                                                                                        CDMN: C. difficile moxalactam norfloxacin
                                                                                                        agar - selective media for culture of C.

                                                                                               Informational documents on C. difficile are
                                                                                               available for reference by healthcare workers
                                                                                               as well as patients and their families on DSM’s
                                                                                               Healthcare workers, please reference this info
                                                                                               under Info for Professionals/Reference Materials
Results That Matter                                                                            /Clinical Microbiology.
DSM’s vision is to provide a high-quality, state-of-the-                                       Patients and their families can access public
art diagnostic system for Manitoba that is known for                                           information under Info for Patients.
its excellent customer service and which is centrally
managed, cost-effective and sustainable
DSM Clinical Microbiology Discipline
Medical Director - Dr. Michelle Alfa                                        1. Schmidt ML, Gilligan PH, Clostridium difficile testing
Technical Director - Shirley Hoban                                         algorithms: What is practical and feasible?, Anaerobe
Microbiology Administration 204.237.2657                                                     (2009), doi:10.1016/j.anaerobe.2009.10.005

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