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Authors: D.C. Allison, C.G. Zalavras*, T. Miller, P. Holtom, S. Schnall, M.J. Patzakis

Title: Bacteriology of Upper Extremity Skin and Subcutaneous Tissue Infections in Injecting Drug Abusers

Addresses: Department of Orthopaedics, LAC+USC Medical Center, University of Southern California, Keck School of Medicine, 1200 N State St, GNH 3900, Los Angeles, CA 90033

Purpose: Drug injection is an increasing problem that often results in soft tissue infections, especially of the upper extremity. The purpose of this study was to determine the distinct bacteriologic features of skin and subcutaneous tissue infections in injecting drug abusers in order to provide guidelines for optimal empiric therapy in these patients.

Methods: All admissions to the musculoskeletal infection ward at our institution from 1993 to 2005 were screened to identify patients with a documented history of injecting illicit drugs and a diagnosis of a skin or subcutaneous tissue infection. Eight hundred fifty-five patients met these criteria and were included in this retrospective study. There were 648 male and 217 female patients with a mean age of 41.5 years (18 to 75 years). Subcutaneous abscesses were present in 839 patients and cellulitis in 16 patients. The infection was located at the hand in 215 patients (25%), the shoulder area in 169 patients (20%), the elbow area in 152 patients (18%), the forearm in 132 patients (15%), the arm in 116 patients (14%), the wrist area in 39 patients (5%), and in multiple locations in 32 patients (3%).

Results: Culture results were available for 792 patients. Cultures were positive in 694 patients (with monomicrobial infections in 366 of 792 patients [46%] and polymicrobial infections in 328 of 792 patients [42%]), whereas in 98 of 792 patients (12%) cultures were negative. In the 694 patients with positive cultures the most common organism was Staphylococcus aureus, identified in 359 patients (52%). Throughout the 13-year period of the study, oxacillin-resistant Staphylococcus aureus (ORSA) was present in 33% of Staphylococcus aureus infections (117 of 359 patients). However, a progressive increase in the proportion of ORSA was observed; ORSA comprised 5% of Staphylococcus aureus infections in 1999, 50% in 2001, 56% in 2003, and 82% in 2005. Among other organisms, Gram-negative rods were identified in 18% of patients (124/694) and anaerobic organisms in 10% of patients (67/694).

Discussion: Staphylococcus aureus is the most common pathogen in infections of the skin and subcutaneous tissue in injecting drug abusers with an increasing proportion of ORSA. In addition to surgical decompression of abscesses, empiric antibiotic therapy should provide coverage for Gram-positive organisms (including ORSA), Gram-negative organisms and anaerobes.

Broad-spectrum antibiotic coverage is necessary for skin and subcutaneous tissue infections in injecting drug abusers.

Musculoskeletal Infecton Society
Musculoskeletal Infecton Society