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Bites, Animal and Human
Kathryn Samai, PharmD, BCPS
Brian James Kimbrell, MD, FACS
image BASICS
DESCRIPTION
  • Animal bites to humans from dogs (60-90%), cats (5-20%), rodents (2-3%), humans (2-3%), and rarely other animals, including snakes
  • System(s) affected: potentially any
Pediatric Considerations
Young children are more likely to sustain bites and have bites that include the face, upper extremity, or trunk.
EPIDEMIOLOGY
  • Predominant age: all ages but children > adults
  • Predominant gender: dog bites, male > female; cat bites, female > male
Incidence
  • 2 to 5 million animal bites per year in the United States
  • Account for 1% of all emergency room visits
  • 1-2% will require hospital admission, and 10 to 20 victims will die from bites annually (1).
ETIOLOGY AND PATHOPHYSIOLOGY
  • Most dog bite wounds are from a domestic pet known to the victim.
  • 89% of cat bites are provoked.
  • Males, pit bull terriers, and German shepherds are most commonly associated with dog bites (2).
  • Human bites are often the result of one 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.
  • 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.
RISK FACTORS
  • 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.
GENERAL PREVENTION
  • Instruct children and adults about animal hazards and strongly enforce animal control laws.
  • Educate dog owners.
image DIAGNOSIS
PHYSICAL EXAM
  • Dog bites (60-90% of bites)
    • Hands and face most common site of injury in adults and children, respectively
    • More likely to have associated crush injury
  • Cat bites (5-20% 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, and lymphangitis.
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 & INTERPRETATION
Initial Tests (lab, imaging)
  • Drainage from infected wounds should be Gramstained and cultured (3)[A].
    • If wound fails to heal, perform cultures for atypical pathogens (fungi, Nocardia, and mycobacteria) and ask lab to keep bacterial cultures for 7 to 10 days (some pathogens are slow-growing).
  • 85% of bite wounds will yield a positive culture, with an average of five pathogens.
  • Aerobic and anaerobic blood cultures should be obtained before starting antibiotics if bacteremia suspected (e.g., fever or chills).
  • Previous antibiotic therapy may alter culture results.
  • Radiographs are needed to check for fractures in clenched-fist injuries.
Follow-Up Tests & Special Considerations
Subsequent suspicion of osteomyelitis warrants comparison of plain radiograph or MRI. Severe skull bites warrant a CT scan and ultrasound can be useful for detection of abscess.
Diagnostic Procedures/Other
Surgical exploration may be needed to ascertain extent of injuries or to drain deep infections (such as tendon sheath infections), especially in serious hand wounds.
Test Interpretation
  • Dog bites (4,5)
    • Pasteurella species is present in 50% of bites.
    • Also found: viridans streptococci, Staphylococcus aureus, Staphylococcus intermedius, Bacteroides, Capnocytophaga canimorsus, Fusobacterium
  • Cat bites (5)
    • Pasteurella species 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 spp., Staphylococcus aureus, Eikenella corrodens (29%), 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.
  • Reptile bites
    • If from a venomous snake, use antivenom. Bacteria: Pseudomonas aeruginosa, Proteus spp., Salmonella, Bacteroides fragilis, and Clostridium spp.
  • Rodent bites
    • Streptobacillus moniliformis or Spirillum minor, which causes rat-bite fever
  • Monkey bites
    • All monkey bites can transmit rabies, and bites of a macaque monkey may transmit herpes B virus, which is potentially fatal.
image TREATMENT
GENERAL MEASURES
  • 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.
  • Monkey bite: Providers should contact CDC and administer an antiviral, such as valacyclovir, active against herpes B virus.
MEDICATION
  • Consider need for antirabies therapy: rabies immunoglobulin and human diploid cell rabies vaccine for those bitten by wild animals (in the United States, primary vector is bat bite), rabid pets, unvaccinated pets, or if animal cannot be quarantined for 10 days.
  • Tetanus toxoid (Td) for those previously immunized but >10 years since their last dose (3)[C]; tetanus, diphtheria, and pertussis (Tdap) is preferred over Td (3)
  • A patient negative for anti-HBs 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, unless blood exposure to broken skin.
  • Preemptive antibiotics are only recommended for human bites and high-risk wounds (deep puncture, crush injury, venous or lymphatic compromise, hands or near joint, face or genital area, immunocompromised hosts, requiring surgical repair, asplenic, advanced liver, edema).
  • P.127

  • For preemptive and for empiric treatment of established infection, amoxicillin and clavulanate is first-line (3)[B],(6)
    • Adults: amoxicillin 875 mg/clavulanate 125 mg PO BID
    • Children: <3 months: 30 mg/kg/day PO q12h; ≥3 months and <40 kg: 45 mg/kg/day q12h; >40 kg, use adult dosing
      • Averse reaction: Amoxicillin and 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: preemptive, 3 to 5 days; treatment of cellulitis/skin abscess, 5 to 10 days; bacteremia, 10 to 14 days
      • Adults: clindamycin (300 mg PO TID) plus either
      • Trimethoprim-sulfamethoxazole (TMP-SMX; 1 DS tablet PO BID-TID) or
      • Ciprofloxacin (500 mg PO BID) for 7 to 21 days
      • Children: clindamycin (5 to 10 mg/kg IV [to a maximum of 600 mg] followed by 10 to 30 mg/kg/day in 3 to 4 divided doses to a maximum of 300 mg per dose) plus
      • TMP-SMX (8 to 10 mg/kg/day of trimethoprim) in 2 divided doses
  • Avoid 1st-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 Pasteurella multocida (dog/cat bites) and E. corrodens (human bites).
Pregnancy Considerations
  • Penicillin-allergic pregnant women
    • Azithromycin 250 to 500 mg PO every day
  • Observe closely and note potential increased risk of failure.
ISSUES FOR REFERRAL
  • Deep wounds to the hand and face should be referred to a hand surgeon or plastic surgeon, respectively.
  • Bites from primates or unusual species of animals should be referred to infectious disease specialist.
SURGERY/OTHER PROCEDURES
  • Copious irrigation of the wound with normal saline via a catheter tip is needed to reduce risk of infection.
  • Devitalized tissue needs débridement.
  • Débridement 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).
  • 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 (8).
  • Delayed primary closure in 3 to 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.
INPATIENT CONSIDERATIONS
Admission Criteria/Initial Stabilization
Patients with deep or severe wound infections, systemic infections requiring IV antibiotics, those requiring surgery, and the immunocompromised require ABCs for associated trauma or severe infection and IV antibiotic therapy
  • Adults: ampicillin and sulbactam 1.5 to 3 g IV q6h or piperacillin and tazobactam 3.375 g IV q6h (3). Alternative: ciprofloxacin 400 mg IV q12h or levofloxacin 750 mg IV every day with metronidazole 500 mg IV q8h (3)
  • Children: ampicillin and sulbactam 200 mg/kg/day IV given in 4 divided doses to a maximum of 3 g per dose
Discharge Criteria
Pending clinical improvement
image ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Patient Monitoring
  • Patient should be rechecked in 24 to 48 hours if not infected at time of first encounter.
  • Daily follow-up is warranted for infections.
  • Subsequent revisions of empiric antibiotic therapy should be based on culture results and clinical response.
PATIENT EDUCATION
Educate parents at well-child checks about how to avoid animal bites.
PROGNOSIS
Wounds should steadily improve and close over by 7 to 10 days.
REFERENCES
1. Goldstein EJ. New horizons in the bacteriology, antimicrobial susceptibility and therapy of animal bite wounds. J Med Microbiol. 1998;47(2):95-97.
2. Wiley JF II. Mammalian bites. Review of evaluation and management. Clin Pediatr (Phila). 1990;29(5):283-287.
3. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Disease Society of America. Clin Infect Dis. 2014;59(2):e10-e52.
4. Bini JK, Cohn SM, Acosta SM, et al. Mortality, mauling, and maiming by vicious dogs. Ann Surg. 2011;253(4):791-797.
5. Abrahamian FM, Goldstein EJ. Microbiology of animal bite wound infections. Clin Microbiol Rev. 2011;24(2):231-246.
6. Medeiros I, Saconato H. Antibiotic prophylaxis for mammalian bites. Cochrane Database Syst Rev. 2001;(2):CD001738.
7. Oehler RL, Velez AP, Mizrachi M, et al. Bite-related and septic syndromes caused by cats and dogs. Lancet Infect Dis. 2009;9(7):439-447.
8. Benson LS, Edwards SL, Schiff AP, et al. Dog and cat bites to the hand: treatment and cost assessment. J Hand Surg Am. 2006;31(3):468-473.
Additional Reading
  • Okonkwo U, Changulani M, Moonot P. Animal bites: practical tips for effective management. J Emerg Nurs. 2008;34(3):225-226.
  • Rittner AV, Fitzpatrick K, Corfield A. Best evidence topic report. Are antibiotics indicated following human bites? Emerg Med J. 2005;22(9):654.
See Also
Cellulitis; Rabies; Snake Envenomation; Bartonella Infections
Codes
ICD10
  • S61.459A Open bite of unspecified hand, initial encounter
  • S01.85XA Open bite of other part of head, initial encounter
  • S20.97XA Other superficial bite of unspecified parts of thorax, initial encounter
Clinical Pearls
  • Wound cleansing, débridement, and culture are essential. Most wounds should be left open.
  • Prophylaxis is recommended for human bites and high-risk wounds.
  • Consider rabies and tetanus vaccination.
  • Antibiotic and duration of therapy should be adjusted based on culture results and clinical improvement.
  • Patients bitten by animals or humans require close follow-up to monitor for infection.