What is the most common causative organism of a hand infection caused by a human bite?

Hand Infection Caused by Human Bite: Causative Organism

The most common causative organism of a hand infection caused by a human bite is Eikenella corrodens, which is found in approximately 30% of human bite wounds. 1

Microbiology of Human Bite Infections

Human bite wounds have a complex polymicrobial nature, with both aerobic and anaerobic organisms typically present:

• Streptococci (especially viridans streptococci) are isolated from approximately 80% of human bite wounds 1
• Staphylococcus aureus is found in about 40% of human bite wounds 1
• Eikenella corrodens, a gram-negative facultative anaerobic bacillus, is present in approximately 30% of human bite wounds 1
• Anaerobes, including Fusobacterium species, peptostreptococci, Prevotella species, and Porphyromonas species, are present in about 60% of cases, usually in mixed culture 1

Clinical Significance of Eikenella corrodens

Eikenella corrodens has particular clinical importance in human bite infections for several reasons:

• It is a characteristic organism in human bite wounds, especially in clenched-fist injuries 1, 2
• Many anaerobes in human bite wounds produce β-lactamases, making them resistant to penicillin and first-generation cephalosporins 1
• E. corrodens requires specific antibiotic coverage that differs from typical empiric choices for skin infections 3, 4
• Infections involving E. corrodens often have delayed presentation and diagnosis, leading to more severe complications 5, 2

Types of Human Bite Wounds and Risk Factors

Human bite wounds can be categorized into different types, with varying infection risks:

• Clenched-fist injuries (when a fist strikes teeth) have the highest risk of infection and complications, with E. corrodens being particularly common 1, 5
• Occlusal bites to the hand also carry significant infection risk 1
• Human bites to areas other than the hand have infection rates similar to animal bites (approximately 10%) 6, 3

Treatment Considerations

When treating hand infections from human bites, consider:

• Early and aggressive irrigation and debridement are essential for preventing infection 1
• Antibiotics effective against E. corrodens should be included in the treatment regimen 1, 4
• Penicillin is effective against E. corrodens, but additional coverage for S. aureus is often needed (such as dicloxacillin or a β-lactam/β-lactamase combination) 1, 3
• Deep hand infections from human bites have high morbidity (up to 27% complication rate) including stiffness, recurrent infection, and other infectious complications 5

Common Pitfalls and Caveats

• Failing to recognize clenched-fist injuries as human bites, leading to inadequate treatment 5, 2
• Using antibiotics that don't cover E. corrodens (such as first-generation cephalosporins alone) 1, 3
• Delayed presentation is common with human bite infections and significantly worsens outcomes 5, 2
• Viral diseases (herpes, hepatitis B and C, HIV) can also be transmitted through human bites and should be considered 1

Human bite wounds to the hand require prompt treatment with appropriate antibiotics covering the polymicrobial nature of the infection, with particular attention to coverage for Eikenella corrodens to prevent serious complications.