327. Evaluation of a Commercial PCR Assay for Detection of Environmental Contamination with Clostridium difficile
Session: Poster Abstract Session: C. difficile Diagnostics
Thursday, October 18, 2012
Room: SDCC Poster Hall F-H
  • Abhishek.pdf (155.3 kB)
  • Background: Contaminated environmental surfaces are an important source for transmission of Clostridium difficile. However, there are currently no efficient and easy to use methods to assess the effectiveness of environmental disinfection.

    Methods: We tested the hypothesis that a commercial real-time polymerase chain reaction (PCR) for the toxin B gene tcdB (Xpert C. difficile, Cepheid) would provide a sensitive and efficient method to detect toxigenic C. difficile in the environment. Pre-moistened swabs and gauze pads were used to culture high-touch surfaces (toilet seat/hand rail, table/bed rail, phone/call button) in C. difficile infection (CDI) rooms before and after post-discharge cleaning by housekeeping. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of PCR from swabs was compared to toxigenic culture by direct plating of swabs.

    Results: Of 22 CDI rooms, 9 were sampled before and 13 were sampled after post-discharge cleaning. One or more C. difficile swab cultures were positive for 6 of 9 active CDI rooms and 6 of 13 (46%) cleaned rooms. PCR testing of swabs was specific but had low sensitivity in comparison to culture (Table). Lowering the PCR cycle threshold (Ct) value to 45 increased sensitivity without decreasing specificity. PCR positivity correlated with greater levels of contamination (5/5 sites positive when ≥10 colonies (range: 11-215) present versus 0/6 when < 10 colonies recovered (P<0.001). In comparison to swabs, gauze cultures had 50% higher site positivity in both active CDI and cleaned rooms.

    Conclusion: In comparison to culture, we found that a commercial PCR assay had good sensitivity for detection of heavy environmental contamination, but poor sensitivity for detection of low levels of contamination that were typically present after rooms were cleaned. Modifications of the assay such as lowering the PCR Ct or increasing the surface area sampled may result in improved sensitivity.

    Table. Diagnostic accuracy of PCR for detection of environmental C. difficile

    No. PCR +/No. culture +

    Sensitivity (%)

    Specificity (%)

    PPV (%)

    NPV (%)

    Active CDI patient in room






    After terminal cleaning






    Active CDI patient in room (Ct < 45)






    After terminal cleaning (Ct < 45)






    Abhishek Deshpande, M.D., Ph.D.1,2, Jennifer Cadnum, B.S.3,4, Brett Sitzlar, B.S.2, Sirisha Kundrapu, M.D.1,2 and Curtis J. Donskey, MD1,2, (1)Infectious Diseases, Case Western Reserve University, Cleveland, OH, (2)Infectious Diseases, Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH, (3)Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH, (4)Case Western Reserve University, Cleveland, OH


    A. Deshpande, None

    J. Cadnum, None

    B. Sitzlar, None

    S. Kundrapu, None

    C. J. Donskey, Pfizer: Grant Investigator, Research support
    Merck: Grant Investigator, Research grant
    GOJO: Consultant and Grant Investigator, Research grant
    Steris: Consultant and Grant Investigator, Research grant
    ViroPharma: Grant Investigator, Research support
    BioK: Consultant, Consulting fee
    3M: Scientific Advisor, Consulting fee
    EcoLab: Consultant, Consulting fee
    Optimer: Grant Investigator, Research grant

    Findings in the abstracts are embargoed until 12:01 a.m. PST, Oct. 17th with the exception of research findings presented at the IDWeek press conferences.