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Data on MRSA, antibiotic-associated diarrhea link on the rise
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BOSTON — There is increasing evidence that suggest methicillin-resistant Staphylococcus aureus is a cause of antibiotic-associated diarrhea, according to a presenter here.
“The paucity of reports in the literature suggest that [methicillin-resistant S. aureus (MRSA)] goes unrecognized in many facilities, partly due to policies recommending against culturing stool specimens of patients who have been hospitalized for more than 3 days, and because MRSA is not widely recognized as a cause of diarrhea by clinical microbiology laboratory personnel,” John M. Boyce, MD, of the Hospital of St. Raphael, told Infectious Disease News. “As a result, clinical labs do not report the presence of heavy growth of MRSA in stool specimens submitted for enteric pathogen cultures.”
For the study, researchers investigated the frequency of C. difficile-associated diarrhea, MRSA-associated antibiotic-associated diarrhea and enterocolitis at a universityaffiliated hospital between 2005 and 2010. Stool samples of 13,477 patients were tested for C. difficile toxin and S. aureus.
Growth on colistin-naladixic acid agar consistent with S. aureus was confirmed as MRSA; specimens yielding heavy MRSA were examined for growth of aerobic gram-negative rods and other gram-positive flora. Patients with specimens positive for C. difficile toxin A/B were classified as having C. difficile-associated diarrhea. Patients with specimens negative for C. difficile toxin and with heavy, pure growth of MRSA and three or more loose stools per day for 2 or more days were classified as MRSA-associated antibiotic-associated diarrhea, according to the researchers.
Results indicated 2,064 patients had C. difficile-associated diarrhea (2.6 cases/1,000 patient-days) and 1,597 had MRSA recovered from the stool. Of which, 786 patients had heavy growth of MRSA in stool and 33 were classified as MRSA antibiotic-associated diarrhea (0.04 cases/1000 patient-days).
“In most patients who have stool specimens positive for MRSA, this represents colonization of the gastrointestinal tract, and therapy is not warranted,” Boyce said. “However, in patients with antibiotic-associated diarrhea, negative stool assays for C. difficile, no other identified enteric pathogen and no evidence that diarrhea is related to medications, MRSA should be considered a possible cause of the diarrhea. In such circumstances, a gram stain of stool showing many gram-positive cocci with morphology consistent with S. aureus and little or no normal flora, and heavy (nearly pure) growth of MRSA in stool specimens are suggestive of antibiotic-associated diarrhea due to MRSA (Boyce JM AM J Gastroenterol 2005;100:1828-34). Oral vancomycin is generally considered the drug of choice for such infections.” – by Ashley DeNyse
For more information:
- Boyce J. #843. Presented at: The IDSA 49th Annual Meeting; Oct. 20-23, 2011; Boston.
Disclosure: The researchers report no relevant financial disclosures.
Boyce and colleagues previously provided evidence that enterotoxigenic methicillin-resistant Staphylococcus aureus (MRSA) strains could be implicated in a small percentage of patients with health care-associated antibiotic associated diarrhea. The present study shows us the relative importance of MRSA as a cause of antibiotic associated diarrhea in one hospital setting. Before the identification of Clostridium difficile as a cause of antibiotic associated diarrhea, S. aureus strains were implicated in serious forms of antibiotic associated diarrhea. This study suggests that S. aureus may have been a cause of antibiotic-associated colitis in these early cases rather than being caused by C. difficile strains that were undetected.
– Herbert DuPont, MD
Infectious Disease News Editorial Board member
Disclosure: Dr. DuPont reports no relevant financial disclosures.
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