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Emergency and Acute Medicine – Human Bite
Overview
Human bites are the third most common type of bite injury, following dog and cat bites. Up to 75% occur during aggressive encounters, while 15–20% are related to sexual activity (“love nips”). Human bites carry a higher risk of infection than animal bites because of the dense oral bacterial flora.
Types of Human Bites
Occlusional bites occur when human teeth directly bite the skin, producing lacerations or crush injuries; these are more prone to infection than animal bites. Clenched-fist injuries (CFIs), also known as fight bites, are the most serious form. They typically present as small wounds over the metacarpophalangeal joints of the dominant hand and occur when a clenched fist strikes another person’s teeth. When the hand relaxes, the puncture site may seal, trapping oral bacteria within the joint. Tendons can carry bacteria into deeper potential spaces of the hand, markedly increasing the risk of deep and extensive infection.
Microbiology and Etiology
Human bite infections are polymicrobial, involving aerobic and anaerobic organisms. The most common pathogens are Streptococcus and Staphylococcus species. Other organisms include Eikenella corrodens, Haemophilus influenzae, Peptostreptococcus, and Corynebacterium. E. corrodens exhibits synergism with Streptococcus, Staphylococcus aureus, Bacteroides, and gram-negative organisms. Although rare, viral transmission through human bites has been reported, including hepatitis viruses, HIV, and herpes simplex virus.
Clinical Presentation
Most human bites involve the upper extremities (60–75%), followed by the head and neck (15–20%), trunk (10–20%), and lower extremities (approximately 5%). Common complications include cellulitis, deep-space infections such as septic arthritis and osteomyelitis, fractures, and tendon injuries. Hand bites have the highest infection rates.
History and Examination
History should include the time of injury, patient allergies, immune status, tetanus immunization status, and HIV or hepatitis B status of the person inflicting the bite, if known. On examination, carefully document wound location and extent, swelling, crush injury, devitalized tissue, range of motion, tendon and nerve function, signs of infection including regional adenopathy, and any joint or bone involvement.
Essential Evaluation
A meticulous examination is critical, especially for clenched-fist injuries. The deepest part of the wound must be examined while the fingers are taken through a full range of motion to identify extensor tendon lacerations or joint capsule violation.
Diagnostic Testing
Aerobic and anaerobic cultures should be obtained from clinically infected wounds; cultures are not indicated for noninfected bites. CBC is appropriate when there are signs of significant infection. Electrolytes, glucose, BUN, and creatinine should be checked in diabetic patients or those with severe infections. Imaging is usually unnecessary, but plain radiographs are indicated for suspected fractures, foreign bodies such as teeth, baseline evaluation when bone or joint space is violated, or infection near bone or joint spaces. Ultrasound may help differentiate abscess from cellulitis.
Differential Diagnosis and Special Considerations
Animal bites typically cause more punctures and lacerations, whereas human bites more often produce crush injuries. In suspected sexual abuse, look for central bruising or “hickeys,” linear abrasions or bruises on both dorsal and palmar or plantar surfaces, and multiple lesions on different extremities. An intercanine distance greater than 3 cm suggests permanent dentition and an attacker older than 8 years. If abuse is suspected, collect saliva using a saline-moistened swab placed in a paper envelope, obtain photographs, and notify authorities.
Prehospital and Initial Management
Control bleeding with direct pressure. Ensure airway patency and adequate tissue perfusion.
Emergency Department Management
Irrigate wounds copiously with normal saline using an 18-gauge needle or plastic catheter directed along the wound tract, avoiding forceful injection into tissues. Débride foreign material, necrotic tissue, and devitalized skin, but do not débride puncture wounds. Remove eschar to allow drainage and irrigation of underlying pus.
Clenched-fist injuries require immobilization and splinting in a functional position with bulky hand dressing, elevation, and early consultation with a hand surgeon for possible operative irrigation and exploration. Use a sling for outpatients and tubular stockinette suspension for inpatients. Do not perform primary repair of avulsion wounds.
Wound Closure
Primary closure increases infection risk and should be avoided in infected wounds or those older than 24 hours. Closure of wounds older than 8 hours is controversial. Facial wounds may be closed up to 24 hours after injury with counseling regarding infection risk. Infected wounds and those presenting after 24 hours should be left open, with possible delayed primary closure or approximation using Steri-Strips. Clenched-fist injuries should never be sutured.
Antibiotic Therapy and Prophylaxis
Prophylactic antibiotics are controversial for low-risk bites but are recommended for moderate to severe injuries, crush injuries with edema, bone or joint involvement, hand bites, wounds near prosthetic joints, and patients with diabetes, prior splenectomy, or immunosuppression. Tetanus prophylaxis should be updated as indicated. Refer patients for possible HIV testing and surveillance when appropriate.
Medications
First-line therapy includes amoxicillin–clavulanate orally, ampicillin–sulbactam IV, piperacillin–tazobactam IV, ticarcillin–clavulanate IV, or ceftriaxone plus metronidazole. Second-line regimens involve combination therapy with trimethoprim–sulfamethoxazole, penicillin VK, ciprofloxacin, or doxycycline, each combined with anaerobic coverage using clindamycin or metronidazole.
Disposition
Admission is indicated for infected wounds at presentation, severe or progressive cellulitis or lymphangitis, systemic infection, or failure of outpatient antibiotics. Healthy patients with localized infection may be discharged on antibiotics with 24-hour follow-up, while noninfected wounds require reassessment within 48 hours.
Special Populations
In geriatric patients, human bite marks rarely occur accidentally and should raise concern for elder abuse. In pediatric patients, human bite marks are also uncommon and suggest possible abuse; an intercanine distance greater than 3 cm indicates an adult attacker.
Follow-Up and Referral
All infected hand wounds require hand specialist follow-up. Suspected child abuse mandates referral to appropriate authorities.
Key Clinical Cautions
Always examine clenched-fist wounds through full finger motion to detect tendon or joint involvement. Early hand surgery consultation is essential for all clenched-fist injuries because of their high infection rate.
Overview
Human bites are the third most common type of bite injury, following dog and cat bites. Up to 75% occur during aggressive encounters, while 15–20% are related to sexual activity (“love nips”). Human bites carry a higher risk of infection than animal bites because of the dense oral bacterial flora.
Types of Human Bites
Occlusional bites occur when human teeth directly bite the skin, producing lacerations or crush injuries; these are more prone to infection than animal bites. Clenched-fist injuries (CFIs), also known as fight bites, are the most serious form. They typically present as small wounds over the metacarpophalangeal joints of the dominant hand and occur when a clenched fist strikes another person’s teeth. When the hand relaxes, the puncture site may seal, trapping oral bacteria within the joint. Tendons can carry bacteria into deeper potential spaces of the hand, markedly increasing the risk of deep and extensive infection.
Microbiology and Etiology
Human bite infections are polymicrobial, involving aerobic and anaerobic organisms. The most common pathogens are Streptococcus and Staphylococcus species. Other organisms include Eikenella corrodens, Haemophilus influenzae, Peptostreptococcus, and Corynebacterium. E. corrodens exhibits synergism with Streptococcus, Staphylococcus aureus, Bacteroides, and gram-negative organisms. Although rare, viral transmission through human bites has been reported, including hepatitis viruses, HIV, and herpes simplex virus.
Clinical Presentation
Most human bites involve the upper extremities (60–75%), followed by the head and neck (15–20%), trunk (10–20%), and lower extremities (approximately 5%). Common complications include cellulitis, deep-space infections such as septic arthritis and osteomyelitis, fractures, and tendon injuries. Hand bites have the highest infection rates.
History and Examination
History should include the time of injury, patient allergies, immune status, tetanus immunization status, and HIV or hepatitis B status of the person inflicting the bite, if known. On examination, carefully document wound location and extent, swelling, crush injury, devitalized tissue, range of motion, tendon and nerve function, signs of infection including regional adenopathy, and any joint or bone involvement.
Essential Evaluation
A meticulous examination is critical, especially for clenched-fist injuries. The deepest part of the wound must be examined while the fingers are taken through a full range of motion to identify extensor tendon lacerations or joint capsule violation.
Diagnostic Testing
Aerobic and anaerobic cultures should be obtained from clinically infected wounds; cultures are not indicated for noninfected bites. CBC is appropriate when there are signs of significant infection. Electrolytes, glucose, BUN, and creatinine should be checked in diabetic patients or those with severe infections. Imaging is usually unnecessary, but plain radiographs are indicated for suspected fractures, foreign bodies such as teeth, baseline evaluation when bone or joint space is violated, or infection near bone or joint spaces. Ultrasound may help differentiate abscess from cellulitis.
Differential Diagnosis and Special Considerations
Animal bites typically cause more punctures and lacerations, whereas human bites more often produce crush injuries. In suspected sexual abuse, look for central bruising or “hickeys,” linear abrasions or bruises on both dorsal and palmar or plantar surfaces, and multiple lesions on different extremities. An intercanine distance greater than 3 cm suggests permanent dentition and an attacker older than 8 years. If abuse is suspected, collect saliva using a saline-moistened swab placed in a paper envelope, obtain photographs, and notify authorities.
Prehospital and Initial Management
Control bleeding with direct pressure. Ensure airway patency and adequate tissue perfusion.
Emergency Department Management
Irrigate wounds copiously with normal saline using an 18-gauge needle or plastic catheter directed along the wound tract, avoiding forceful injection into tissues. Débride foreign material, necrotic tissue, and devitalized skin, but do not débride puncture wounds. Remove eschar to allow drainage and irrigation of underlying pus.
Clenched-fist injuries require immobilization and splinting in a functional position with bulky hand dressing, elevation, and early consultation with a hand surgeon for possible operative irrigation and exploration. Use a sling for outpatients and tubular stockinette suspension for inpatients. Do not perform primary repair of avulsion wounds.
Wound Closure
Primary closure increases infection risk and should be avoided in infected wounds or those older than 24 hours. Closure of wounds older than 8 hours is controversial. Facial wounds may be closed up to 24 hours after injury with counseling regarding infection risk. Infected wounds and those presenting after 24 hours should be left open, with possible delayed primary closure or approximation using Steri-Strips. Clenched-fist injuries should never be sutured.
Antibiotic Therapy and Prophylaxis
Prophylactic antibiotics are controversial for low-risk bites but are recommended for moderate to severe injuries, crush injuries with edema, bone or joint involvement, hand bites, wounds near prosthetic joints, and patients with diabetes, prior splenectomy, or immunosuppression. Tetanus prophylaxis should be updated as indicated. Refer patients for possible HIV testing and surveillance when appropriate.
Medications
First-line therapy includes amoxicillin–clavulanate orally, ampicillin–sulbactam IV, piperacillin–tazobactam IV, ticarcillin–clavulanate IV, or ceftriaxone plus metronidazole. Second-line regimens involve combination therapy with trimethoprim–sulfamethoxazole, penicillin VK, ciprofloxacin, or doxycycline, each combined with anaerobic coverage using clindamycin or metronidazole.
Disposition
Admission is indicated for infected wounds at presentation, severe or progressive cellulitis or lymphangitis, systemic infection, or failure of outpatient antibiotics. Healthy patients with localized infection may be discharged on antibiotics with 24-hour follow-up, while noninfected wounds require reassessment within 48 hours.
Special Populations
In geriatric patients, human bite marks rarely occur accidentally and should raise concern for elder abuse. In pediatric patients, human bite marks are also uncommon and suggest possible abuse; an intercanine distance greater than 3 cm indicates an adult attacker.
Follow-Up and Referral
All infected hand wounds require hand specialist follow-up. Suspected child abuse mandates referral to appropriate authorities.
Key Clinical Cautions
Always examine clenched-fist wounds through full finger motion to detect tendon or joint involvement. Early hand surgery consultation is essential for all clenched-fist injuries because of their high infection rate.
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