INTRODUCTION

Skin and soft-tissue infections, comprising abscess, cellulitis, and necrotizing soft-tissue infection (NSTI), account for 1.8 million annual emergency department (ED) visits in the United States alone (Table 43.1). There has been a recent dramatic shift in bacteriology, with a rise in the prevalence of staphylococcal infection and of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), requiring new empiric antibiotic strategies. Emergency physicians are often in a position to make the first diagnosis and treatment of skin and soft-tissue infections. In the case of potentially lethal NSTI, highly time-dependent morbidity and mortality require familiarity with diverse presentations and the limitations of diagnostic tests.

EPIDEMIOLOGY

Abscess

Risk factors for abscess formation include injection drug use (IDU), shaving, and known colonization or infection with CA-MRSA. Staphylococcus aureus is implicated in 19–71% of abscess cases. It is highly prevalent, colonizing approximately 30% of the general population and an even higher proportion of injection drug users, diabetics, and health care workers. The rising prevalence of CA-MRSA in the United States has manifested largely as a rise in spontaneous skin and soft-tissue infections. Nearly all S. aureus strains secrete exotoxins (including hemolysins, nucleases, proteases, lipases, hyaluronidase, and collagenase) that convert host tissues into nutrients required for bacterial growth. Additionally, some methicillin-sensitive S. aureus (MSSA) and the majority of CA-MRSA strains carry genes for Panton-Valentine leukocidin (PVL), a cytotoxin causing leukocyte destruction, tissue necrosis, and enhanced abscess formation.