INJECTION DRUG USERS SKIN INFECTIONS

Skin and Soft Tissue Infections in injection drug users
Unique features of skin infections in the injection drug user include a high rate of skin and pharyngeal colonization with S. aureus and streptococcal species, and the high frequency with which cutaneous abscesses are caused by oral flora. Conflicting evidence exists as to whether HIV seropositivity confers additional risk for the development of skin abscesses.

The injection drug user will self-inject, often multiple times a day, with nonsterile needles, which may be licked prior to injection. Tap water, toilet water, or saliva often are used to dissolve narcotics, and each has been implicated in harboring causative organisms in both skin and blood-borne infections. Female gender is associated with an increased incidence of skin infections because of a relatively high rate of skin injection (skin popping).

Local infections of the skin and soft tissue include cellulitis, subcutaneous abscesses, septic phlebitis, necrotizing fasciitis, Fournier's gangrene, gas gangrene, and pyomyositis. Cellulitis is typically caused by S. aureus and Streptococcus spp. Cultures from cutaneous abscesses are often polymicrobial, with aerobic gram-negative rods, anaerobic cocci, and bacilli. Quinine, used to "cut" heroin, may increase the risk of abscess formation.

The extensive interconnected abscesses produced by skin-popping provide ideal growth conditions for Clostridium botulinum and C. tetani. Broken needles lodged in the skin are foreign bodies that potentiate infection. Groin injection has been associated with local gangrene, as well as with the development of rapidly progressive and fatal Fournier gangrene. Cutaneous abscesses in the neck may involve the carotid triangle and produce airway obstruction, vocal cord paralysis, and laryngeal edema.

Presenting signs and symptoms of cutaneous infections, including pyomyositis, are fever, pain, localized erythema, and edema. The painful area should be carefully inspected for fluctuance, crepitance, and lymphangitis. Infections over venipuncture sites suggest infected pseudoaneurysms. Pulsatile masses must be imaged with ultrasonography prior to incision and drainage, as attempts to aspirate or incise and drain an infected pseudoaneurysm can result in significant hemorrhage. Angiography may be required to identify vasospasm, thrombosis, emboli, mycotic aneurysms, or septic hematomas.

Plain radiographs can demonstrate air in the soft tissues. Computed tomography delineates the involvement of other structures and the extent of deep abscesses, especially in complex areas such as the neck. Whenever crepitus or subcutaneous air is detected or deep tissue or muscle involvement is suspected clinically, a surgical consultation for possible exploration or debridement is appropriate. Wound botulism and tetanus have been reported in injection drug users, and tetanus immunization status should be updated appropriately.

injection drug users with superficial cellulitis without evidence of systemic involvement can be managed as outpatients with oral antibiotics to cover streptococci and staphylococci. Febrile or toxic-appearing patients, or those not responding to outpatient treatment, require hospital admission. Blood and wound cultures should be obtained, and broad-spectrum intravenous antibiotics initiated pending culture results. Coverage should include penicillinase-resistant synthetic penicillin or vancomycin plus an antipseudomonal aminoglycoside, antipseudomonal penicillin, or cephalosporin. Surgical consultation is indicated for deep tissue and necrotizing soft tissue infections.