Microbiology of upper extremity soft tissue abscesses in injecting drug abusers

Drug injection often results in upper extremity soft tissue infections. We determined the bacteriology of soft tissue abscesses in substance abusers who inject drugs to provide guidelines for empiric antibiotic therapy. We retrospectively studied 855 patients (638 men and 217 women; mean age, 41.5 years) with a history of injecting illicit drugs and a diagnosis of an upper extremity soft tissue abscess. In the 694 patients with positive cultures the most common organism was Staphylococcus aureus, identified in 359 of 694 patients (52%). An increase in the incidence of oxacillin-resistant S. aureus over time was observed. Oxacillin-resistant S. aureus comprised 5% of S. aureus infections in 1999, 50% in 2001, 56% in 2003, and 82% in 2005. Microaerophilic streptococci were present in 37% of culture-positive cases and other anaerobes in 10%. Infections were monomicrobial in 366 of 694 patients (53%) and polymicrobial in 328 of 694 patients (47%). S. aureus is the most common pathogen in soft tissue abscesses in injecting drug abusers with an increasing incidence of oxacillin-resistant S. aureus. In addition to surgical decompression of abscesses, broad-spectrum empiric antibiotic therapy is necessary.