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

Causative Organisms of Hand Infection Due to Human Bite

The most common causative organism of hand infection due to a human bite is Eikenella corrodens, found in approximately 30% of human bite wounds, followed by Streptococcus species (80%) and Staphylococcus aureus (40%). 1

Microbiology of Human Bite Wound Infections

• Human bite wound infections are typically polymicrobial, involving a mixture of aerobic and anaerobic bacteria from the oral cavity 2, 3
• The primary pathogens include:
  • Eikenella corrodens - characteristic of human bite wounds 1, 4
  • Streptococcus species, especially viridans streptococci (80% of cases) 1, 3
  • Staphylococcus aureus (40% of cases) 1, 5
  • Anaerobic bacteria (present in about 60% of cases) including:
    • Fusobacterium species
    • Peptostreptococci
    • Prevotella species
    • Porphyromonas species 2, 1

Clinical Significance and Complications

• Hand infections from human bites can progress rapidly due to the unique anatomy of the hand and the virulent nature of oral flora 3
• Complications can include:
  • Cellulitis and local abscesses 2, 5
  • Septic arthritis, particularly with "fight-bite" injuries that penetrate the metacarpophalangeal joint 4, 3
  • Tenosynovitis and osteomyelitis 2
  • Rare but serious complications include endocarditis, meningitis, brain abscess, and sepsis 2

Diagnostic Considerations

• Proper specimen collection is crucial for accurate diagnosis:
  • Tissue samples or aspirates are preferred over swabs 2
  • Gram stain should be performed to assess for inflammation indicators and microorganisms 2
  • Both aerobic and anaerobic cultures should be obtained 2, 1
• Many anaerobes in human bite wounds produce β-lactamases, making them resistant to penicillin and first-generation cephalosporins 1

Treatment Approach

• Early and aggressive irrigation and debridement are essential for preventing infection progression 1, 3
• Empiric antibiotic therapy should cover the common pathogens:
  • Antibiotics effective against E. corrodens should be included in the treatment regimen 1
  • Beta-lactam antibiotics with beta-lactamase inhibitors are recommended for bite wounds 4
  • For MRSA coverage, consider appropriate antibiotics based on local resistance patterns 6, 5
• Wound closure may need to be delayed depending on contamination and infection severity 3

Common Pitfalls and Caveats

• Human bites can also transmit viral diseases such as herpes, hepatitis B and C, and HIV 1, 3
• "Fight-bite" injuries (clenched-fist injuries) have a high risk of joint penetration and require careful evaluation for septic arthritis 4, 3
• Failure to recognize the polymicrobial nature of these infections can lead to inadequate antimicrobial coverage 2, 1
• Delayed presentation is common and associated with worse outcomes 3, 5