845. Trends in Methicillin-Resistant Staphylococcus aureus (MRSA) Gastrointestinal Colonization and Antibiotic-Associated Diarrhea (AAD). 
Session: Oral Abstract Session: MRSA - Epidemiological Trends
Saturday, October 22, 2011: 9:00 AM
Room: 157ABC
Background:  Clostridium difficile (Cdiff) is the most common cause of AAD, accounting for 15 – 20% of cases. S. aureus, including MRSA, is a recognized cause of enterocolitis and AAD, but the frequency of these syndromes is unknown and few cases are reported.  We report on the relative frequency of Cdiff-associated diarrhea (CDAD) and MRSA-associated AAD and enterocolitis.

Methods:   From 2005 through 2010, all stool specimens submitted for Cdiff toxin assays at a university-affiliated hospital were tested for Cdiff toxin using enzyme immunoassay (EIA) or combined 2-step antigen/EIA methods and were inoculated onto colistin-naladixic acid (CNA) agar and incubated for 48 hrs.  Patients (pts) with a stool positive for Cdiff toxin A/B were defined as CDAD. Growth on CNA consistent with S. aureus was recorded as heavy, moderate or few and confirmed as MRSA using chromogenic MRSA selective media.  Stool specimens were examined for growth of aerobic gram-negative rods and other gram-positive flora. Pts with stools specimens negative for Cdiff toxin and with heavy, pure growth of MRSA plus > 3 loose stools/day for > 2 days were classified as MRSA AAD, and their medical records were reviewed. As a proxy for accessory gene regulator activity, MRSA isolates from MRSA AAD pts were tested for delta-toxin production by agar plate assay using S. aureus RN 4220. 

Results:  In the 6-yr study period, 13,477 unique pts had stool specimens tested for Cdiff toxin on >1 occasion, and 2064 (15.3%) pts were classified as CDAD cases (2.6 cases/1000 pt-days [recurrences excluded]). 1597 (11.8%) pts had MRSA recovered from the stool. For 808 (50.6%) pts, the stool MRSA isolate was the first MRSA recovered from the pt. 786 (49.2%) pts had heavy growth of MRSA in stool, and 33/1597 (2.0%) were classified as MRSA-associated AAD with an overall rate of 0.24% (33/13477 pts screened), or 0.04 cases/1000 pt-days). Of 33 MRSA AAD cases, most had abdominal pain, 28 (85%) had an abdominal CT scan performed, and 15 (45%) had bowel thickening on CT scan.  13 pts received oral vancomycin.  Severity of illness did not correlate with delta-toxin production.    

Conclusion:  In the 6-yr period, CDAD was 62 times more common than MRSA AAD.  A majority (61%) of pts with MRSA-associated AAD improved without specific therapy.

Subject Category: N. Hospital-acquired and surgical infections, infection control, and health outcomes including general public health and health services research

John Boyce, MD1,2 and Nancy Havill, MT1, (1)Medicine, Hospital of St. Raphael, New Haven, CT, (2)Yale University School of Medicine, New Haven, CT


J. Boyce, Becton Dickinson: Research support for a previous study, Research support

N. Havill, None

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