Skin and soft tissue infections in injection drug users.

Skin and soft tissue infections are the most common cause for hospital admission of injection drug users. Cutaneous and subcutaneous abscesses are the most frequent type of SSTI and occur most commonly when drug users are no longer able to inject intravenously and resort to injection directly into skin or muscle. Abscesses may be difficult to differentiate from uncomplicated cellulitis or may be confused with pseudoaneurysms, hematoma, phlegmon, or thrombosed vein. Special studies, including ultrasonography; CT scans, and MR imaging; or careful incision and inspection may be necessary to clarify the extent of infection and the presence of abscess. These procedures may also help differentiate a subcutaneous abscess from a vascular structure. Uncomplicated cellulitis most commonly responds to antibiotic therapy directed toward Staphylococcus aureus and Streptococcus spp. In several recent studies, cutaneous and subcutaneous abscesses have been found to be caused by polymicrobial infections and to include anaerobic organisms as well as aerobic gram-positive cocci in a little more than 50% of cases. Complete, often repeated, incision and drainage is a prerequisite for successful outcome in these cases. Complications of SSTI are many and are potentially life threatening. They include direct extension of subcutaneous abscess into vital areas or structures, necrotizing fasciitis and myositis, bacteremia, and sepsis. An outbreak of a highly lethal SSTI that recently occurred in Scotland, Ireland, and England seems to have resulted from infection with Clostridia spp, including C. novyi and C. perfringens. A rare but well-documented SSTI in injection drug users is pyomyositis, an abscess-forming infection of skeletal muscle. More than 20 cases have been reported in temperate climates to date. Although not life-threatening, chronic cutaneous venous ulcers of the lower extremities are common and debilitating, requiring long-term multidisciplinary care for successful healing.