1363. Utility of Repeating a Clostridium difficile PCR Test within 7 Days of a Negative Result
Session: Poster Abstract Session: Clostridium difficile
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
  • GJH-poster-1363- final.pdf (7.2 MB)
  • Background:

    Nucleic acid amplification tests (e.g. PCR) for toxigenic Clostridium difficile are much more sensitive than immunoassays; however, there are limited data on whether performing PCR on a second specimen following an initial negative test increases detection of C. difficile. Since switching to a C. difficile PCR test, we have permitted repeat testing >24 hrs after a negative specimen, or >7 days after a positive. Previous studies suggest that repeating a negative test within 7 days has a low yield. We performed a retrospective review to determine how often a negative C. difficileresult was followed by a positive within 7 days and whether there were distinctive clinical features associated with conversions.


    All C. difficile PCR tests performed at Stony Brook University Hospital during 2011-2012 were reviewed. Samples were tested with the Cepheid Xpert C. difficile test from Jan 2011 to Aug 2012 and the Xpert C. difficile/Epi test from Sep to Dec 2012. An Excel spreadsheet was used to identify repeat specimens and calculate time intervals.


    8048 C. difficile tests were performed on patients ≥ 18 years old. 3142 patients had a single test and 1542 patients had ≥ 2 tests (mean 3.2). Among patients who had a single C. difficile test, 491 (15.6%) had a positive result. A negative specimen was repeated within 7 days in 1075 cases; 35 (3.3%) of these repeats converted to positive; the median repeat interval is 4 days for both negative-to-negative and negative-to-positive. The majority of the conversions occurred in bone marrow transplant and oncology patients (n=11) or patients on other medical services (n=17). Chart review did not identify a unique clinical pattern. 3/12 of negative-to-posi conversions tested with the C. difficile/Epi assay were positive for the Epi component (027/NAP1/BI).


    Repeating a negative C. difficile test within 7 days identified a small percentage of infected patients. Restrictions on test ordering may need to be tailored to specific populations.

    Guo Jun Huang, MD, Department of Medicine, Stony Brook University Medical Center, Stony Brook, NY, Rekha Sivadas, MD, Department of Medicine, Stony Brook University, Stony Brook, NY, Silvia Spitzer, PhD, Molecular Genetics Laboratory, Stony Brook University Medical Center, Stony Brook, NY and Eric Spitzer, M.D., Ph.D., Department of Clinical Microbiology, Stony Brook University Medical Center, Stony Brook, NY


    G. J. Huang, None

    R. Sivadas, None

    S. Spitzer, None

    E. Spitzer, None

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