Human and Animal Bitewounds - Overview and Management

Case Study

S: Patient is an 18 year old mulatto female who presents to the Emergency Room c/o multiple dog bites to her right lower extremity. She states that she was riding a horse approximately 1 1/2 hours prior to arrival and was attacked by a large mixed breed dog. Attack was unprovoked except that patient was probably riding through the dog's yard. The dog's behavior was not considered aberrant by the patient and the dog was unknown to the patient. Her boyfriend notified Animal Control and the dog was picked up for observation. She had been treated with hydrogen peroxide PTA. Her last tetanus shot had been 1 year prior.

O: Afebrile. VSS.
P. E. was unremarkable except for numerous lacerations and puncture wounds to her right lower extremity between midthigh and upper calf. There was one 3cm-square skin and subcutaneous defect extending to the muscle approx. 3 cm below the knee posteriorly. Most of the wounds were posterior and had little debris in them. Only minor bleeding present. FROM. Neurovascular intact.

C: The patients wounds were soaked in betadine solution and then carefully cleaned. They were lavaged with approximately 2 liters of G. U. irrigant (normal saline plus neosporin solution). Large wounds were packed open with wet to dry dressings, and she was given Augmentin 500 mg P.O. q 6 hours. She was given instructions for cleaning and was followed every day for a week. On follow-up, she showed no signs of infection. She is presently healing well, and Surgery is considering secondarily closing the large defect using a small drain. Patient continues to do well.

Incidence and Statistics

1995 - Over 100 million dogs and cats in U.S.

• Between 1 and 2 million dog bites reported each year.
• Dogs responsible for approx. 85% of bite wounds.
  1/3 of all animal bites occur in children.
• 85% of dog bites and 80% of cat bites are inflicted by animals belonging to victem's family or a neighbor.
• approx. 1/2 are considered provoked.
• facial injuries more common in children.
• In 1992 - bites account for 1% of all ER visits.
• 10,000 hospitalizations annually.
• 10 - 20 reported deaths annually.
• Cost in medical care estimated at $5-30 million/yr.

Wounds

• Dog bites may deliver 150-450 lb per sq inch - enough for a crush injury.
• Puncture wounds and wounds to hands and joints are more likely to become infected.
• Site - hands (48-59%), arms (16-26%), lower limbs (15%), and face (8-30%).
• Human bites often more serious and often involve hands.

Human Bites

2 types

• Occlusional injuries - mostly to fingers but can be on arms, breasts, or genital areas.
• Clinched-fist injuries usually involve metacarpophalangeal joint of the dominant hand. May be associated with fractures.

Hand wounds are usually more serious than wounds elsewhere.

Microbiology - Common Pathogens

• S. aureus
• Eikenalla corrodens
• Various anaerobic species - most frequently Bacteroides sp.
• Alpha hemolytic streptococci - E. corrodens and alpha hemolytic strep act synergistically in causing indolent and serious infections.

Dog and Cat Bites

Dog bites can cause puncture wounds, lacerations, and crush injuries.

Dog bites may contain:

• Pasteurella multocida - in about 25% of cases.
• mixed anaerobes
• Staphylococcus aureus

Cat bites are often puncture wounds.

Cat bites may contain:

• Pasteurella multocida - in about 50 - 74% of cases.
• other aerobes and anaerobes including S. aureus.

Treatment of Bite Wounds

1. Get history including what first-aid was given before arrival.
2. Administer appropriate tetanus prophylaxis.
3. Anesthetize the wound appropriately.
4. Wash all lacerations and puncture wounds for at least 15 minutes with a 20% soap solution, benzalkonium chloride, or betadine.
5. Debride meticulously and aseptically all nonviable tissue. Remove all foreign particles.
6. Irrigate wounds thoroughly with at least 1000 cc normal saline. Consider using pressure lavage.
7. Administer prophylactic antibiotics if the wound was on the hand or arm or if the animal's teeth penetrated to the bone or tendon sheath, or if wound is more than 8 hours old.
8. Splint extensively lacerated arms or legs.
9. Elevate...Lack of elevation is most common cause of treatment failure.
10. Call animal control.

Rabies

Most cases in wild animals because of widespread pet vaccination.

Most common in Southeast, esp. Florida, Georgia and Alabama.

Dx made by direct immunofluorescence test on animal brain.

Transmission - Animals secrete virus in their saliva.

• Time of secretion before clinical symptoms in animals varies:
• Cats up to 2 days
• Dogs up to 3 days
• skunks up to 18 days
• bats up to several months

Virus enters organism via bite wound and travels up peripheral nerves at rate of 3 mm/hr. When it reaches the brain the patient develops clinical rabies and the prognosis is grave.

If a domestic animal has bitten someone, call animal control so they can capture, isolate and observe the animal for 10 days; determine its vaccination status. If it neither becomes ill nor dies during this period, rabies prophylaxis is unnecessary.

To all patients meeting the following criteria, administer human rabies immune globulin, 20 IU/kg as a single dose and begin the human diploid cell rabies vaccine course, 1 mL I.M. on days 1, 3, 7, 14, 28, and 90:

• Bitten by a wild animal, sick or well, especially one that behaved aberrantly (such as attacking during the daylight, near human habitation); skunks, bats, foxes, and raccoons are likely rabies carriers.
• Bitten by a domestic animal that was ill or behaved aberrantly.
• Bitten by a stray domestic animal that was not captured, in a community that has a high incidence of rabies in wild animals (contact the local public health services for info.)
• Bitten by a wild animal, sick or well, that is being kept as a pet.

Antimicrobial Treatment

Given by most MD's with any but very minor wounds.

Animal Bites

• Augmentin - covers most of organisms found in bite wounds.
• Tetracycline can be used as an alternative (especially in PCN allergic patients) to Augmentin but it is contraindicated in pregnant or lactating women and children.
• Erythromycin has poor activity against P. multocida but is probably next best if Augmentin or Tetracycline can't be used. Careful follow-up is important.
• P. multocida is resistant to penicillin and penicillinase resistant penicillins (i.e. dicloxacillin) in 18-50% of cases.
• Keflex shows poor activity against P. multocida as well.

Human Bites

• Augmentin is active against the entire spectrum of human bite wound pathogens including S. aureus and E. corrodens and the penicillinase producing anaerobes.
• Infected clinched-fist injuries often need IV antibiotics. Cefitoxin is a satisfactory drug. Wound cultures should be obtained before start of treatment.
• S. aureus is often resistant to penicillins while E. corrodens is usually resistant to penicillinase resistant penicillins and 1st generation cephalosporins.

Summary

• Clean well
• Give antibiotics
• Follow up closely

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