10.19 Bites

agk’s Library of Common Simple Emergencies

Presentation

Histories of animal bites are usually volunteered, but the history of a human bite, such as one obtained over the knuckle during a fight, is more likely to be denied or explained only after questioning. A single bite may contain various types of injury, including underlying fractures and tendon and nerve injuries, not all of which are immediately apparent.

What to do:

• Obtain a complete history, including the type of animal that bit, whether or not the attack was provoked, what time the injury occurred, the current health status and vaccination record of the animal, and whether or not the animal has been captured and is being held for observation. report the bite to police or appropriate local authorities.
• Assess the wound for any damage to deep structures, any need for surgical consultation, and any risk of infection. Look for bone and joint involvement and, if present, obtain appropriate imaging studies (dog bites have caused open depressed skull fractures in small children). Examine for nerve and tendon injury and be aware that crush and puncture wounds as well as bites on the hands, wrists and feet are at higher risk for development of infection and significant complications such as tenosynovitis, septic joints, osteomyelitis and sepsis. Bites from cats, humans, other primates are also associated with higher rates of infection. If tissue damage is extensive, then obtain vascular, orthopedic, otorhinolaryngologic, reconstructive or other consultation.
• For crush wounds and contusions, elevate above the heart and apply cold packs.
• If the wound requires debridement, or will be painful to cleanse and irrigate, anesthetize with buffered lidocaine (epinephrine will slightly increases infection rates).
• If there are already signs of infection, obtain aerobic and anaerobic cultures of any pus.
• Cleanse the wound with antiseptic (10% povidone-iodine solution, diluted 1:10 in normal saline) and sharply debride any debris and non-viable tissue.
• Irrigate the wound, using a 20ml syringe, a 19 gauge needle or an irrigation shield (Zerowet), and at least 200ml of sterile saline or the diluted 1% povine-iodine solution. This technique demonstrably reduces microscopic debris and bacteria. You can use an intravenous setup to irrigate a large area.
• Prepare every wound as if you were going to suture it.
• For animal bite wounds that are clean, uninfected lacerations located anywhere other than the hand or foot, you may staple, tape, or suture them closed. Prophylactic antibiotics are not necessary. Infection rates in sutured dog bite wounds have compared favorably with those for unsutured wounds and with non-bite lacerations.
• If the wound is infected when first seen, plan either a delayed repair after three to five days of saline dressings or secondary wound healing without closure. Prescribe antibiotics (see below) for seven to ten days. Severe infections require hospitalization for elevation, immobilization, intravenous antibiotics and surgical consultation.
• With human bites, animal bites that are punctures or located on the hand, wrist or foot, or bites more than 12 hours old, in most cases, you should leave the wounds open and apply a light dressing or saline dressing and consider delayed primary closure after two to three days. Wounds should also be left open on debilitated and patients with diabetes, alcoholism, chronic steroid use, organ transplants, vascular insufficiency, splenectomy, HIV or other immunocompromising condition.
• Start prophylactic antibiotics in the ED on these wounds (see above) and in patients with artificial or damaged heart valves and implanted prosthetic devices. The most effective dose is the one you can give now. Augmentin 500 mg tid for three to five days is the current CDC recommendation for all bites. Alternatives for prophylaxis include:
  • dog bites: clindamycin (Cleocin) 150-300 mg and ofloxacin (Floxin) 400 mg bid for adults, clindamycin and trimethoprim/sulfamethoxazole for children
  • cat bites: penicillin V 500 mg qid, doxycycline 100 mg bid for adults, or ceftriaxone 500-2000 mg im/iv
  • human bites: cefoxitin 2000 mg q8h iv
• If the patient has had no tetanus toxoid in the past 5-10 years, provide prophylaxis.
• If the patient was bitten by an oddly behaving domestic animal, or a bat, coyote, fox, opossum, raccoon, or skunk, you should start rapid rabies vaccination with 20IU/kg of rabies immune globulin and the first of five l mL doses of human diploid strain rabies vaccine. Reassure the patient that bites of rodents and lagomorphs, including rats, squirrels, hamsters, and rabbits, in America do not usually transmit rabies. Such bites also have a low incidence of secondary infection and do not require prophylactic antibiotics.
• Provide hepatitis prophylaxis for patients who have been bitten by known carriers of hepatitis B. Administer hepatitis B immune globulin 0.06ml/kg im at the time of injury and schedule a second dose in 30 days. Follow standard guidelines applicable to contaminated needle sticks.
• Minimize edema (and infection) of hand wounds by splinting and elevation.
• Have patient return for a wound check in two days, or sooner if there is any sign of infection. Explain the potential for serious complication such as septic arthritis, osteomyelitis and tenosynovitis (evident when a finger becomes diffusely swollen, immobile, tender along the flexor surface or painful on passive extension) which will require specialty consultation.

What not to do:

• Do not overlook a puncture wound.
• Do not suture debris, non-viable tissue, or a bacteria innoculum into a wound.
• Do not use buried absorbable sutures, which act as a foreign body and cause a reactive inflammation for about a month and increase the risk of infection.
• Do not waste time and money obtaining cultures and Gram stains of fresh wounds. The results of these tests do not correlate well with the organisms that subsequently cause infection.
• Do not routinely suture human bites.

Discussion

Animal bites are often brought promptly to the ED, if only because of a legal requirement to report the bite, or because of fear of rabies. Bite wounds account for 1% of all ED visits in the US, most caused by dogs and cats. Most dig bites are from household pets rather than strays. A disproportionate number of dog bites are from German shepherds.

Bites occur most commonly among young, poorly supervised children who disturb the animals while they are sleeping or feeding, separate them during a fight, try to hug or kiss an unfamiliar animal or accidently frighten it. Malpractice claims and other civil lawsuits often follow bite injuries.

Dog and cat bites both show high rates of infection with staphylococcus and streptococcus species, as well as Pasteurella multocida and many different gram-negative and anaerobic bacteria. In addition to these organisms, 10-30% of all human bites are infected with Eikenella corrodens, which sometimes show resistance to the semisynthetic penicillins, but sensitivity to penicillin. Adequate debridement and irrigation are clearly more effective than prophylactic antibiotics, and except in wounds that are at high risk for developing infection are often all that is required to prevent infection of bites.

Less than 0.1% of all animal bites result in rabies. For questions of local rabies risk, local public health services may be available and valuable support as sources of information regarding the area’s prevalence of rabies in an involved species.

References:

• Rosen RA: The use of antibiotics in the initial management of recent dog-bite wounds. Am J Emerg Med 1985;3:19-23.
• Elenbaas RM, McNabney WK, Robinson WA: Evaluation of prophylactic oxacillin in cat bite wounds. Ann Emerg Med 1984;13:155-157.
• Dire DJ, Hogan DE, Riggs MW: A prospective evaluation of risk factors for infections from dog-bite wounds. Acad Emerg Med 1994;1:258-266.

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