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The bacterial etiology of hand infections depends on the source of the offending inoculum. Because Staphylococcus and Streptococcus species routinely colonize the skin, they are the bacteria most frequently isolated from hand infections. Polymicrobial infections, including anaerobes, are also common, especially when mouth flora contaminates wounds. In most U.S. cities, community-associated methicillin-resistant Staphylococcus aureus (MRSA) is now the most common pathogen cultured from patients with skin and soft tissue infections in EDs,1 including 47% to 73% of hand infections.2–6 However, local rates of MRSA disease vary.7

Injection drug users typically present with abscesses or deep space infections secondary to S. aureus and gram-negative organisms.8 Infections are most commonly caused by direct introduction of a contaminated needle through inadequately cleansed skin, but hematogenous spread from bacterial endocarditis should also be considered (see Chapter 294, Injection Drug Users).

Paronychia and felons are commonly caused by minor trauma associated with chewing fingernails or exposing minor injuries to saliva. Most of these infections are polymicrobial in origin, with most harboring anaerobic bacteria.

Bacteria found in infections caused by animal bites reflect the oral flora of the involved species. Bites introduce a broad range of bacteria, including gram-positive, anaerobic, and gram-negative organisms. Human bites are typically polymicrobial, with a median of four organisms (three aerobes and one anaerobe). Common pathogens in human bites include S. anginosus (52%), Fusobacterium nucleatum (32%), S. aureus (30%), Eikenella corrodens (30%), and Prevotella melaninogenica (22%).9Amoxicillin-clavulanic acid or moxifloxacin has the best activity against these organisms.9 Cat and dog bites may harbor Pasteurella multocida, which typically produces an aggressive, rapidly spreading cellulitis that quickly becomes suppurative. Pasteurella is also sensitive to penicillin and ampicillin, and antibiotic coverage is the same as that indicated for human bites.10 For a complete discussion on animal bites, see Chapter 50, Puncture Wounds and Bites.

Patients with diabetes or acquired immunodeficiency syndrome may harbor atypical infections caused by Mycobacterium or Candida albicans. Patients who are immunocompromised or asplenic may be at risk for rapidly progressive and fatal infections. Aggressive intervention is indicated in these settings.

General Principles of Evaluation and Management

Hand infections are most commonly introduced by an injury to the dermis. The infection initially may remain superficial, as a cellulitis, or localized, as a paronychia or felon. Left untreated, infections ultimately may spread along anatomic planes or to adjacent compartments in the hand. Deeper injuries may directly seed underlying structures, giving rise to rapidly spreading infections such as those seen with closed fist injuries or cat bites. Rarely, hematogenous seeding may be the source of hand infections.11,12

Obtain a directed history to delineate a likely cause of the infection. Patients who present with systemic symptoms secondary to a hand infection are seriously ill, and parenteral antibiotics with ...

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