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Community-Acquired Resistant S. aureus: Info for Clinical Decision Making

Methicillin-resistant Staphylococcus aureus (MRSA) has been a healthcare-related problem for decades, but recently we have seen a marked increase in community-acquired MRSA (CA-MRSA). In this prospective cohort study of patients with MRSA infection identified at 12 laboratory facilities in Minnesota, investigators compared the epidemiologic features and resistance patterns of CA-MRSA and healthcare-associated MRSA (HA-MRSA).

Of 1100 MRSA infections, 131 (12%) were community-associated, and 937 (85%) were healthcare-associated (3% could not be classified). CA-MRSA infection was more common in younger patients (mean age, 23 for CA-MRSA patients vs. 68 years for HA-MRSA patients). CA-MRSA was most often isolated from skin and soft tissue infections (75% of cases), and the most common associated medical conditions in children were dermatologic. CA-MRSA isolates were significantly more likely than HA-MRSA isolates to express the Panton Valentine leukocidin genes, which code for the production of cytotoxins that cause tissue necrosis. The antimicrobial susceptibilities also differed. Isolates from CA-MRSA were significantly more likely than HA-MRSA isolates to be sensitive to erythromycin (44% vs. 9%), clindamycin (83% vs. 21%), ciprofloxacin (79% vs. 16%), and gentamicin (94% vs. 80%). At least 90% of both types of MRSA were susceptible to tetracycline and trimethoprim-sulfamethoxazole (TMP/SMX). CA-MRSA isolates were most likely to be sensitive to TMP/SMX (95%), gentamicin, clindamycin, and ciprofloxacin. All isolates were sensitive to vancomycin.

Comment: This study provides more evidence that we may need to change our approach to skin and soft tissue infections in the outpatient setting. Although these data were obtained in a slightly older population, the same issues and principles apply to the pediatric population. Empiric therapy should be started only after culturing the organism and testing for sensitivity. An antistaphylococcal penicillin or a first-generation cephalosporin (the sensitivity and resistance patterns are the same) may be the first-line treatment only in patients who are systemically well. TMP/SMX and clindamycin are probably the best second-line drugs, but resistance can be induced with use, so it is critical to monitor the response carefully.

— Peggy Sue Weintrub, MD

Published in Journal Watch Pediatrics and Adolescent Medicine February 2, 2004

Citation(s):

Naimi TS et al. Comparison of community- and health care-associated methicillin-resistant Staphylococcus aureus infection. JAMA 2003 Dec 10; 290:2976-84.

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