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159 Does healthcare setting impact the diagnostic yield of repeat Clostridium difficile toxin testing by enzyme immunoassay in patients with an initially negative test result?

Saturday, April 2, 2011
Trinity Ballroom (Hilton Anatole)
Farrin Manian, MD, MPH , St John's Mercy Medical Center, Saint Louis, MO
Alex Bryant, Pharm, D , St John's Mercy Medical Center, Saint Louis, MO
Jennifer Manian, BA , St John's Mercy Medical Center, Saint Louis, MO
Background: Whether an initially negative stool Clostridium difficile (CD) toxin enzyme immunoassay (EIA) test should be repeated is unclear, particularly in healthcare settings other than acute care hospitals.   

Objective: To compare the diagnostic yield of repeat CD EIA toxin assay testing within 96 hrs of an initially negative test in hospital, extended-care and outpatient settings. 

Methods: CD toxin testing for cytotoxin A and B was performed by EIA on stool samples from hospitalized patients, those in extended-care facilities (1 nursing home, 1 rehabilitation center, and 1 long-term acute care facility), and outpatients from January-June, 2009.  Formed stools were rejected by the laboratory.  

Results: Of 3390 CD tests received by the laboratory during the study period, 42 were credited (e.g. formed stool) and 1 was not performed for unclear reason(s), resulting in a total of 3347 tested stool samples (2537 unique patients) for analysis, of which 282 (8.4%) were toxin-positive.  The rates of positivity of the 2nd CD test ordered within 96 hrs of an initially EIA negative stool sample were as follows: hospitalized patients, 12/481 (2.5%), extended care facilities, 2/61 (3.3%), and outpatients, 6/80 (7.5%).  There was no significant difference between the rates of positive 2nd CD test in hospitalized and extended-care patients (O.R. 1.3, 95% C.I. 0.2-3.5).  However, outpatients were significantly more likely to have a positive repeat 2nd CD test compared to hospitalized and extended-care patients combined (O.R. 3.1, 95% C.I. 1.1-8.2) or hospitalized patients alone (O.R. 3.2, 95% C.I. 1.1-8.7).  

Conclusions: Compared to hospitalized patients, CD testing by EIA in outpatients is significantly more likely to yield positive repeat 2nd test within 96 hrs of an initially negative test. Whether this finding is related to suboptimal handling of stool specimens obtained from outpatients or other factors deserves further study.