566. Effect of Antibiotics on Community-Associated Methicillin-Resistant Staphylococcus aureus (MRSA) Colonization in Patients with Uncomplicated MRSA Skin Abscesses
Session: Poster Abstract Session: MRSA Surveillance and Infection Prevention
Friday, October 21, 2011
Room: Poster Hall B1

Current IDSA guidelines suggest that incision and drainage alone may be adequate for management of uncomplicated community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) skin abscess.  However, treatment failure and recurrent abscesses are reported in patients not receiving antibiotics.  As MRSA colonization is a risk factor for skin abscess, we hypothesized that including antibiotics in management of MRSA skin abscess decreases MRSA colonization.


From 2008-2010, 896 adults and children with MRSA skin abscesses were enrolled at St. Louis Children’s and Barnes-Jewish Hospitals.  Baseline MRSA colonization status was determined by nares, axilla, and groin cultures; these were repeated in 2-8 weeks.  Antibiotic use was ascertained from medical records and patient interview. 


Of 896 patients, 839 (94%) were prescribed antibiotics, most often clindamycin (54%) or trimethoprim-sulfamethoxazole (TMP-SMX) (51%).  Overall, 65 (7%) received an antibiotic not active against MRSA.

Patients already taking antibiotics at the time of screening were somewhat less likely to be MRSA colonized than those not yet on antibiotics (316 of 472, 67% vs. 308 of 424, 73%, p=0.07).  Patients not MRSA colonized at screening had been taking antibiotics for more days than those colonized (mean 2.67 ± 3.11 vs. 1.77 ± 2.14, p<0.01).  

Of 147 patients MRSA colonized at screening and with a follow-up culture, those prescribed an antibiotic active against MRSA were less likely to be MRSA colonized at follow-up than those not prescribed an antibiotic active against MRSA (56 of 142, 39% vs. 5 of 5, 100%, p=0.01).  Those prescribed clindamycin were less likely to be MRSA colonized at follow-up than those prescribed TMP-SMX (16 of 54, 30% vs. 30 of 56, 53.6%, p=0.01).


Most patients received antibiotics for MRSA abscess.  MRSA colonization was less prevalent in patients already on antibiotics at enrollment.  Patients prescribed antibiotics active against MRSA were less likely to be MRSA colonized at follow-up.  Though resolution of acute abscess after drainage may be unchanged by antibiotic administration, the impact of managing MRSA abscess without antibiotics on ongoing MRSA colonization and recurrent infection requires further study.

Subject Category: C. Clinical studies of bacterial infections and antibacterials including sexually transmitted diseases and mycobacterial infections (surveys, epidemiology, and clinical trials)

Patrick G. Hogan, MPH1, Marcela Rodriguez, MD1, David Hunstad, MD2, Bernard C. Camins, MD, MSCR3 and Stephanie A. Fritz, MD1, (1)Pediatric Infectious Diseases, Washington University School of Medicine, St Louis, MO, (2)Washington University, St. Louis, MO, (3)Department of Medicine, Washington University School of Medicine, St. Louis, MO


P. G. Hogan, None

M. Rodriguez, None

D. Hunstad, None

B. C. Camins, Pfizer, Inc. : Consultant, Grant Investigator and Speaker's Bureau, Consulting fee, Research grant, Research support and Speaker honorarium

S. A. Fritz, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.