Bite, Animal, Emergency Medicine

Basics

Description

Most bites are from provoked animals.
Dog bite wounds:
- Large dogs inflict the most serious wounds (pit bulls cause the most human fatalities).
- Most fatalities in children (70%) due to bites to face/neck
- Dogs of family or friends account for most bites.
Cat bite wounds:
- Majority from pets known to victim
- 50% infection rate in those seeking care
- Puncture wounds most frequent due to sharp thin teeth causing deep inoculation of bacteria
Catscratch disease (CSD):
- 3 of the following 4 criteria:
  - Cat contact, with presence of scratch or inoculation lesion of the skin, eye, or mucous membrane
  - Positive CSD skin test result
  - Characteristic lymph node histopathology
  - Negative results of lab studies for other causes of lymphadenopathy
Rat bite wounds:
- Occur in lab personnel or children of low socioeconomic class
- Rat-bite fever (RBF), rare in US but high mortality rate
- Rat bites rarely transmit rabies, and prophylaxis not routine

Etiology

Dog and cat bites:
- Pasteurella multocida is the major organism in both:
  - Twice as likely to be found in cat bites than dog bites
  - Gram-negative aerobe found in up to 80% of cat infections
  - Infection appears in <24 hr
- Staphylococcus or Streptococcus:
  - Infection appears in >24 hr
- Other organisms include anaerobes and Capnocytophaga canimorsus (dogs).
Catscratch disease:
- Caused by Bartonella henselae
Rat bites:
- Caused by Spirillum minus and Streptobacillus moniliformis (RBF)

Diagnosis

Signs and Symptoms

Distribution of mammalian bites:
- Dog bites represent 80-90% of all bites.
- Cat bites represent 5-15% of all bites.
- Human bites represent 2-5% of all bites (see "Human Bite" chapter).
- Rat bites represent 2-3% of all bites.
Dog bites:
- Appearance:
  - Crush injuries (most common), tears, avulsions, punctures, and scratches
- Low rates of infection compared with cat and human bites
- Infections usually present with:
  - cellulitis
  - malodorous gray discharge
  - fever
  - lymphadenopathy
Cat bites:
- Appearance:
  - Puncture wounds (most common)
  - Abrasions
  - Lacerations
- High infection rates (30-50%) due to deeper puncture wounds
Catscratch disease:
- From the bite/scratch of a cat, dog, or monkey
- Small macule or vesicle that progresses to a papule:
  - Begins several days (3-10) after inoculation
  - Resolves within several days or weeks
  - Regional lymphadenopathy occurs 3 wk postinoculation
  - Tender
  - Nonsuppurative
  - Resolves after 2-4 mo
- Low-grade fever, malaise, headache
Rat-bite fever:
- Does not have to involve a bite. Can occur from handling of rats
- S. moniliformis:
  - Begins several days (2-10) after exposure
  - Common in US
  - Fever, rigors, migratory polyarthralgias, headaches, nausea, and vomiting
- S. minus
  - Incubation period from 1-3 wk
  - More common in Asia
  - Arthritis not common

History

Animals behavior, provocation, location, ownership
Time since attack
Past medical history: Conditions compromising immune function, allergies, and tetanus status

Physical Exam

Record the location and extent of all injuries.
Document any swelling, crush injuries, or devitalized tissue.
Note the range of motion of affected areas.
Note the status of tendon and nerve function.
Document any signs of infection, including regional adenopathy.
Document any joint or bone involvement.

Diagnosis Tests & Interpretation

Lab

Aerobic and anaerobic cultures from any infected bite wound
Cultures not routinely indicated if wounds not clinically infected
Catscratch disease:
- Presence of elevated titers of B. (Rochalimaea) henselae, or
- Positive reaction to catscratch antigen (CSA):
  - Inject 0.1 mL CSA IM
  - Induration at the site 48-72 hr later equal to or exceeding 5 mm is positive

Imaging
Plain radiograph indications:

Fracture
Suspect foreign body (e.g., tooth)
Baseline film if a bone or joint space has been violated in evaluating for osteomyelitis
For infection in proximity to a bone or joint space

Differential Diagnosis

Human bite injuries: Human teeth cause crush injuries and animal teeth cause more punctures and lacerations.
Bite injuries from other animals
CSD-caused lymphadenopathy:
- Reactive hyperplasia (leading cause of lymphadenopathy in children <16 yr)
- Infection, chronic lymphadenitis, drug reaction, malignancy, and congenital conditions

Treatment

Pre-Hospital

Apply pressure to any bleeding wound

Initial Stabilization/Therapy

Achieve hemostasis on any bleeding wound.
Airway stabilization if bite located on face or neck

Ed Treatment/Procedures

Wound irrigation:
- Copious volumes of normal saline irrigation with an 18G plastic catheter tip aimed in the direction of the puncture.
- Avoid injection of saline through tissue planes due to force of irrigation.
D ©bridement:
- Remove foreign material, necrotic skin tags, or devitalized tissues.
- Do not d ©bride puncture wounds.
- Remove any eschar present so underlying pus may be expressed and irrigated.
Wound closure:
- Closing wounds increases risk of infection and must be balanced with scar formation and effect of leaving wound open to heal secondarily.
- Do not suture infected wounds or wounds >24 hr after injury.
- Repair of wounds >8 hr: Controversial
- Close facial wounds (warn patient of high risk of infection).
- Infected wounds, those presenting >24 hr after the event, and deep hand wounds should be left open.
- May approximate the wound edges with Steri-Strips and perform a delayed primary closure.
Antibiotic indications:
- Infected wounds
- Cat bites
- Hand injuries
- Severe wounds with crush injury
- Puncture wounds
- Full-thickness puncture of hand, face, or lower extremity
- Wounds requiring surgical d ©bridement
- Wounds involving joints, tendons, ligaments, or fractures
- Immunocompromised patients
- Wounds presenting >8 hr after the event
Elevate injured extremity
Tetanus prophylaxis
Rabies immunoprophylaxis:
- Not required if rabies not known or suspected
- Rodents (squirrels, hamsters, rats, mice) and rabbits rarely transmit the disease.
- Skunks, raccoons, bats, and foxes represent the major reservoir for rabies.
- See "Rabies" chapter for treatment guidelines.
Catscratch disease:
- Analgesics
- Apply local heat to affected nodes.
- Avoid lymph node trauma.
- Disease usually self-limiting
- Antibiotics controversial, consider if severe disease is present or immunocompromised victim
Rat-bite fever:
- High mortality (10%)
- IV penicillin or doxycycline

Medication

First Line

Amoxicillin/clavulanic acid (Augmentin): 500/125 mg (peds: 40 mg/kg/24h) q8h PO
Ampicillin-sulbactam (Unasyn): 3 g q6h IV
Penicillin 1-2 million units q6h IV (peds 20,000-50,000 U/kg/d div. q4h IV)
Piperacillin-Tazobactam (Zosyn): 4.5 g q8h IV
Ticarcillin-clavulanate (Timentin): 3.1 g q4h IV
Ceftriaxone (Rocephin): 1 g/d plus Metronidazole (Flagyl): 500 mg q8h

Second Line

2 drug therapy: 1 of the following below + anaerobic coverage:
- Trimethoprim-sulfamethoxazole (Septra DS): 1 tablet q12h (peds: 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per day divided into 2 daily doses) PO
- Penicillin (Penicillin VK): 500 mg (peds: 50 mg/kg/24h) PO q6h
- Ciprofloxacin (Cipro): 500-750 mg q12h PO or 400 mg q12h IV
- Doxycycline: 100 mg PO BID
+ (anaerobic coverage):
- Clindamycin (Cleocin): 150-450 mg (peds: 8-20 mg/kg/24h) PO q6h or 600-900 mg (peds: 20-40 mg/kg/24h) IV q8h
- Metronidazole (Flagyl): 500 mg PO TID (peds: 10 mg/kg/dose TID)

Follow-Up

Disposition

Admission Criteria

All bites:
- Infected wounds at presentation
- Severe/advancing cellulitis/lymphangitis
- Signs of systemic infection
- Infected wounds that have failed to respond to outpatient (PO) antibiotics
Catscratch disease:
- Prolonged fever, systemic symptoms, and/or marked lymphadenopathy

Discharge Criteria

Healthy patient with localized wound infection:
- Discharge on antibiotics with 24-hr follow-up.
Noninfected wounds:
- 48-hr follow-up

Follow-Up Recommendations

Hand specialist referral/follow-up for infected hand wounds.
Healthy patient with localized wound infection: Discharge on antibiotics with 24-hr follow-up.
48-hr follow-up for noninfected wounds

Pearls and Pitfalls

Animal bites must be reported to authorities in many localities.

Additional Reading

Baddour L. Soft tissue infections due to dog and cat bites. UpToDate. 2009.
Brook I. Microbiology and management of human and animal bite wound infections. Prim Care. 2003;30(1):25-39.
Elliott SP. Rat bite fever and Streptobacillus moniliformis. Clin Microbiol Rev. 2007;20:13-22.
Galloway RE. Mammalian bites. J Emerg Med. 1998;6:325-331.
Griego RD, Rosen T, Orengo IF, et al. Dog, cat, and human bites: A review. J Am Acad Dermatol. 1995;33:1019-1029.
Klein JD. Cat scratch disease. Pediatr Rev. 1994;15(9):348-353.
Pickering L. Red Book: 2003 Report of the Committee on Infectious Diseases. 26th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2003.
Smith PF, Meadowcroft AM, May DB. Treating mammalian bite wounds. J Clin Pharm Ther. 2000;25:85-99.
Trucksis M. Rat-bite fever. UpToDate. May 6, 2011.

Codes

ICD9

873.40 Open wound of face, unspecified site, without mention of complication
874.8 Open wound of other and unspecified parts of neck, without mention of complication
882.0 Open wound of hand except finger(s) alone, without mention of complication
V01.5 Contact with or exposure to rabies
078.3 Cat-scratch disease
879.8 Open wound(s) (multiple) of unspecified site(s), without mention of complication

ICD10

S01.80XA Unspecified open wound of other part of head, init encntr
S11.90XA Unsp open wound of unspecified part of neck, init encntr
S61.409A Unspecified open wound of unspecified hand, init encntr
Z20.3 Contact with and (suspected) exposure to rabies
A28.1 Cat-scratch disease

SNOMED

399907009 Animal bite wound (disorder)
283738008 Dog bite of face (disorder)
283745008 Dog bite of neck (disorder)
283782004 Cat bite - wound (disorder)
283786001 Rat bite - wound (disorder)
283809003 Animal bite of hand (disorder)
406561001 Animal bite to human by potentially rabid animal (disorder)
79974007 Cat scratch disease (disorder)

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