- Animal bites to humans from dogs (85–90%), cats (5–10%), rodents (2–3%), humans (2–3%), and other animals, including snakes
- System(s) affected: Potentially any
Young children are more likely to sustain bites and 50% may have bites to the face.
- Predominant age: All ages, but children > adults
- Predominant gender: Dog bites: Male > Female; cat bites: Female > Male
- 4–5 million dog bites per year in the US
- Account for 1% of all emergency room visits
- 20% of bites will require medical attention, 10,000 will require hospital admission, and an average of 19 victims will die from the bites annually (1).
- Male dogs and older dogs are more likely to bite.
- Clenched-fist human bites are frequently associated with the use of alcohol.
- Patients presenting >8 hours following the bite are at greater risk of infection.
- Instruct children and adults about animal hazards and strongly enforce animal control laws.
- Educate dog owners.
- Animal bites can cause tears, punctures, scratches, avulsions, or crush injuries.
- Contamination of wound with flora from the mouth of the biting animal or from the broken skin of the victim can lead to infection.
- Most bite wounds are from a domestic pet known to the victim.
- 89% of cat bites are provoked.
- Pit bull terriers, German shepherds, Rottweilers, and mixed breeds are most commonly associated with bites (2).
- Human bites are often the result of 1 person striking another in the mouth with a clenched fist.
- Bites can also occur incidentally in the case of paronychia due to nail biting, or thumb sucking, or “love nips” to the face, breasts, or genital areas.
- Obtain detailed history of the incident (provoked or unprovoked).
- Type of animal
- Vaccine status
- Site of the bite
- Geographic setting
- Dog bites (85–90% of bites):
- Hands and face most common site of injury in adults and children, respectively
- More likely to have associated crush injury
- Cat bites (5–10% of bites):
- Predominantly involve the hands, followed by lower extremities, face, and trunk
- Human bites (2–3% of bites):
- Intentional bite: Semicircular or oval area of erythema and bruising, with or without break in skin
- Clenched-fist injury: Small wounds over the metacarpophalangeal joints from striking the fist against another’s teeth
- Signs of wound infection include fever, erythema, swelling, tenderness, purulent drainage, lymphangitis.
Cat bites (often puncture wounds) are twice as likely to cause infection as dog bites, with higher risks of osteomyelitis, tenosynovitis, and septic arthritis.Pediatric Considerations
If human bite mark on child has intercanine distance >3 cm, bite probably came from an adult and should raise concerns about child abuse.
Diagnostic Tests and Interpretation
Follow-Up and Special Considerations
- Drainage from infected wounds should be Gram-stained and cultured:
- If wound fails to heal, perform cultures for atypical pathogens(fungi, nocardia. and mycobacteria) and ask lab to keep bacterial cultures for 7–10 days (some pathogens are slow-growing).
- 85% of bite wounds will yield a positive culture, with an average of 5 pathogens.
- Blood cultures should be obtained before starting antibiotics if bacteremia suspected (e.g., fever or chills).
Previous antibiotic therapy may alter culture results.ImagingInitial Imaging Approach
Follow-Up and Special Considerations
- If bite wound is near a bone or joint, a plain radiograph is needed to check for bone injury and to use for comparison later if osteomyelitis is subsequently suspected.
- Radiographs are needed to check for fractures in clenched-fist injuries.
Subsequent suspicion of osteomyelitis warrants comparison plain radiograph or MRI.Diagnostic Procedures/Other
Surgical exploration may be needed to ascertain extent of injuries, or drain deep infections (such as tendon sheath infections) especially in serious hand wounds.Pathological Findings
- Dog bites (3,4):
- Pasteurella sp. is present in 50% of bites.
- Also found: Viridans streptococci, Staphylococcus aureus, Staphylococcus intermedius, Bacteroides, Capnocytophaga canimorsus, Fusobacterium
- Cat bites:
- Pasteurella sp. is present in 75% of bites.
- Also found: Streptococcus spp. (including Streptococcus pyogenes), Staphylococcus spp. (including methicillin-resistant Staphylococcus aureus [MRSA]), Fusobacterium spp., Bacteroides spp., Porphyromonas spp., Moraxella spp.
- Human bites:
- Streptococcus species, S. aureus, Eikenella corrodens, and various anaerobic bacteria (e.g., Fusobacterium, Peptostreptococcus, Prevotella, and Porphyromonas spp.)
- Although rare, case reports have suggested transmission of viruses such as hepatitis, HIV, and herpes simplex (5)[C].
- Reptile bites:
- If from a venomous snake, need to use antivenom. Bacteria: P. aeruginosa, Proteus spp., Salmonella, Bacteroides fragilis, and Clostridium spp.
- Rodent bites:
- Streptobacillus moniliformis or Spirillum minor, which cause rat-bite fever
Asplenic patients and those with underlying hepatic disease are at risk of bacteremia and fatal sepsis after dog bites infected with Capnocytophaga canimorsus
- Consider need for antirabies therapy: Rabies immunoglobulin and human diploid cell rabies vaccine for those bitten by wild animals (in US, primary vector is bat bite), rabid pets, or unvaccinated pets, or if animal cannot be quarantined for 10 days (6)[A].
- Tetanus toxoid for those previously immunized, but >5 years since their last dose and tetanus immunoglobulin and tetanus vaccination in patients without a full primary series of immunizations (7)[A]
- A patient negative for anti-HBs antibodies and bitten by an HBsAg-positive individual should receive both hepatitis B immunoglobulin (HBIG) and hepatitis B vaccine.
- HIV postexposure prophylaxis is generally not recommended for human bites, given the extremely low risk for transmission.
- Prophylactic antibiotics are only recommended for human bites and all penetrating animal bites to the hand (8,9)[A].
- For prophylaxis and for empiric treatment of established infection, amoxicillin-clavulanate is first line (6)[B]:
- Adults: 500 mg PO t.i.d. or 875 mg PO b.i.d.
- Children: <3 months: 30 mg/kg/d PO q12h; ≥3 months and <40 kg: 45 mg/kg/d q12h; >40 kg, use adult dosing
- Adverse reaction: Amoxicillin-clavulanate should be given with food to decrease GI side effects.
- Precautions: Dose antibiotics by body weight and renal function.
- Significant possible interactions: Antibiotics may decrease efficacy of oral contraceptives.
- Duration of therapy: Prophylaxis: 3–5 days; treatment: Cellulitis/skin abscess: 5–10 days; bacteremia: 10–14 days. Antibiotic and duration of therapy should be adjusted based on culture results and clinical improvement:
- Adults: Clindamycin (300 mg PO q.i.d.) plus either:
- TMP-SMX (1 DS tablet PO b.i.d.–t.i.d.) or
- ciprofloxacin (500 mg PO b.i.d.) (6)[B] for 7–21 days
- Children: Clindamycin (5–10 mg/kg IV [to a maximum of 600 mg] followed by 10–30 mg/kg/d in 3–4 divided doses to a maximum of 300 mg per dose) plus
- Trimethoprimsulfamethoxazole (8–10 mg/kg of trimethoprim) or
- Cefoxitin IM/IV until culture results obtained
- Avoid: first-generation cephalosporins (e.g., cephalexin), penicillinase-resistant penicillins (e.g., dicloxacillin), macrolides (e.g., erythromycin), and clindamycin (when not administered with another agent) as they lack activity against P. multocida (dog/cat bites) and Eikenella corrodens (human bites) (6)[B].
- Penicillin-allergic pregnant women:
- Azithromycin 250–500 mg PO every day (6)[B]
- Observe closely and note potential increased risk of failure.
Consider community-acquired MRSA as possible pathogen (from human skin or colonized pet). If high suspicion, doxycycline or trimethoprim-sulfamethoxazole provide good coverage (7
Issue for Referral
- Elevation of the injured extremity to prevent swelling
- Contact the local health department regarding the prevalence of rabies in the species of animal involved (highest in bats).
- Snake bite: If venomous, patient needs rapid transport to facility capable of definitive evaluation. If envenomation has occurred, patient should receive antivenom. Be sure patient is stable for transport; consider measuring and/or treating coagulation and renal status along with any anaphylactic reactions before transport.
Deep wounds to the hand and face should be referred to a hand surgeon or plastic surgeon, respectively.
- Copious irrigation of the wound with normal saline via a catheter tip is needed to reduce risk of infection.
- Devitalized tissue needs debridement.
- Debridement of puncture wounds is not advised.
- Primary closure can be considered if the wound is clean after irrigation and bite is <12 hours old, and in bites to the face (cosmesis) (10)[B].
- Infected wounds and those at risk of infection (cat bites, human bites, bites to the hand, crush injuries, presentation >12 hours from injury) should be left open (11)[B].
- Delayed primary closure in 3–5 days is an option for infected wounds.
- Splint hand if it is injured.
- Large, gaping wounds should be reapproximated with widely spaced sutures or Steri-Strips.
Initial Stabilization ABCs for associated trauma or severe infection
- Patients with deep or severe wound infections, systemic infections requiring IV antibiotics, those requiring surgery, and the immunocompromised
- If hospitalized with established infection (animal or human bite):
- Adults: Ampicillin/sulbactam 1.5–3 g IV q6h or piperacillin/tazobactam 3.375 g q6h or 4.5 g IV q8h or ticarcillin/clavulanate 3.1 g IV q4–6h (6)[B]
- Alternative: Ciprofloxacin 400 mg IV q12h or levofloxacin 500 mg IV every day with metronidazole 500 mg IV q8h
- Children: Ampicillin/sulbactam 100–200 mg/kg/d IV given in 4 divided doses to maximum of 3 g per dose
Pending clinical improvement
- Patient should be rechecked in 24–48 hours if not infected at time of first encounter (12)[B].
- Daily follow-up is warranted for infections.
- Subsequent revisions of empiric antibiotic therapy should be based on the culture results and the clinical response.
Wounds should steadily improve and close over by 7–10 days.
- Septic arthritis
- Extensive soft tissue injuries with scarring
- Gas gangrene
- Posttraumatic stress disorder
Daly JS, Scharf MJ. Bites and stings of terrestrial and aquatic life. In Fitzpatrick TB, Eisen AZ, Wolff K, et al. (eds). Dermatology in General Medicine, 7th ed. New York: McGraw Hill; 2011.
Cellulitis; Rabies; Snake Envenomations; Bartonella Infections
- 879.8 Open wound(s) (multiple) of unspecified site(s), without mention of complication
- 879.9 Open wound(s) (multiple) of unspecified site(s), complicated
T14.8 Other injury of unspecified body region
- 399907009 Animal bite wound (disorder)
- 262555007 human bite - wound (disorder)
- Wound cleansing, debridement, and culture are essential. Most wounds should be left open.
- Prophylaxis is recommended for human bites and bites to the hand.
- Consider rabies and tetanus vaccination.
- Patients bitten by animals or humans require close follow-up to monitor for infection.
Jennifer S. Daly, MD
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