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Trends in Prescribing β-Lactam Antibiotics for Treatment of Community-Associated Methicillin-Resistant Staphylococcus aureus Infections

Kalpana Gupta,^1,2* Ann MacIntyre,^2,4 Gary Vanasse,^3, and Louise-Marie Dembry^2,4

Department of Medicine, VA Connecticut Health Care System, West Haven, Connecticut, and,¹ Sections of Infectious Diseases,² Hematology, Department of Medicine, Yale University School of Medicine,³ Quality Improvement Support Services Department, Yale-New Haven Hospital, New Haven, Connecticut⁴

Received 27 July 2007/ Returned for modification 21 September 2007/ Accepted 10 October 2007

Rates of prescribing of β-lactam antibiotics as initial empirical therapy for patients with skin and soft tissue infections (SSTIs) caused by molecularly and epidemiologically characterized community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) isolates were assessed over a 3-year period. A prospectively developed database was used to calculate the prevalence of CA-MRSA SSTIs from 2004 to 2006. Molecular characterization of the MRSA isolate and medical record review for assessment of initial antimicrobial therapy were performed on a subset of patients. Among 2,636 patients with S. aureus SSTIs, the prevalence of CA-MRSA was 9% in 2004, 16% in 2005, and 21% in 2006 (P < 0.0001, chi-square test for trend). Seventy-five percent of CA-MRSA isolates tested were of the USA 300 or 400 clone type. Ninety-two percent of CA-MRSA isolates tested were positive for Panton-Valentine leukocidin, of which 90% carried staphylococcal chromosomal cassette mec type IV. The rate of use of a β-lactam antibiotic as initial empirical therapy for patients with CA-MRSA SSTIs was 86%, 77%, and 60% in 2004, 2005, and 2006, respectively (P = 0.04, chi-square test for trend). Thirty percent of β-lactam-treated patients had a documented risk factor for CA-MRSA infection. The use of a β-lactam antibiotic as initial empirical therapy for CA-MRSA SSTIs has decreased significantly over the past 3 years. However, even as the prevalence of CA-MRSA SSTIs approaches 25%, the majority of patients are still receiving inactive antimicrobial therapy. Further evaluation of the outcomes associated with discordant therapy for CA-MRSA SSTIs is needed.

Published ahead of print on 17 October 2007.

Present address: Department of Medicine, Division of Hematology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.