What is the most likely causative organism of hand infection due to a human bite?

Eikenella corrodens is the Causative Organism of Hand Infection Due to Human Bite

The most likely causative organism of hand infection due to a human bite is Eikenella corrodens (answer D), a gram-negative facultative anaerobic bacillus found in approximately 30% of human bite wounds. 1

Microbiology of Human Bite Infections

Human bite wounds have a complex polymicrobial flora that reflects the normal oral microbiome of the biter. According to current guidelines, the bacteriologic profile typically includes:

• Streptococci (especially viridans streptococci) - present in 80% of wounds 1
• Staphylococcus aureus - present in 40% of wounds 1
• Eikenella corrodens - present in 30% of wounds 1
• Anaerobes - present in 60% of cases, including:
  • Fusobacterium species
  • Peptostreptococci
  • Prevotella species
  • Porphyromonas species 1

While multiple organisms are typically present in human bite infections, E. corrodens has special clinical significance because:

1. It is uniquely associated with human bite wounds, particularly clenched-fist injuries 2
2. It requires specific antibiotic coverage that differs from typical empiric therapy for skin infections 3
3. Infections involving E. corrodens can lead to serious complications if not properly treated 4

Clinical Presentation and Complications

Human bite wounds to the hand are particularly concerning because:

• They are frequently more serious than animal bites 1
• The hand's anatomy (joints and tendons in close proximity to skin) increases risk of deep structure involvement 5
• Delayed presentation is common, especially with clenched-fist injuries 2
• E. corrodens grows slowly, potentially delaying diagnosis 2

Complications of untreated E. corrodens infections can include:

• Cellulitis
• Tenosynovitis
• Septic arthritis
• Osteomyelitis 4

Management Considerations

When managing hand infections from human bites:

• All wounds should be cultured both aerobically and anaerobically 3
• Empiric antibiotic therapy should cover both common pathogens and E. corrodens 3
• Surgical evaluation is essential for puncture wounds or severe lacerations 5
• Delayed treatment significantly increases complication rates 6

Important Clinical Pitfalls

1. Antibiotic selection pitfall: E. corrodens is sensitive to penicillin but resistant to first-generation cephalosporins and clindamycin, unlike S. aureus 4, 6. This makes appropriate empiric antibiotic selection critical.

2. Diagnostic pitfall: E. corrodens grows slowly and may be missed with routine culture techniques, potentially leading to treatment failure 2.

3. Management pitfall: Suturing human bite wounds, especially on the hand, significantly increases complication rates 6.

In summary, while multiple organisms are typically present in human bite infections, E. corrodens represents a uniquely important pathogen due to its prevalence, antibiotic resistance pattern, and association with serious complications when not properly treated.