OVERVIEW: What every practitioner needs to know

Are you sure your patient has been bitten? What are the typical findings for this condition?

Key signs of a dog bite are abrasions, puncture wounds, and/or lacerations, which may include avulsed tissue. Cat bites are puncture wounds. Human bites are secondary to occlusion injury or clench-fist injury.

Initial signs and symptoms may include pain, erythema, edema, and ecchymosis. One should also assess for devitalized tissue and/or purulent drainage, as this may alter the treatment plan.

Microbiologic Characteristics

Bite wound infections are polymicrobial (aerobic and anaerobic) and depend predominantly on the oral flora of the biter. Environment and the victim’s skin flora also play a role. Approximately 10%-15% of dog bites become infected. The leading pathogens for dog bites are Pasteurella species, (specifically P. multocida and P. canis), Streptococcus species, Staphylococcus species, Capnocytophaga canimorsus , and anaerobes.

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Comparatively, there is a wide spectrum of incidence of cat bite infection, with anywhere from 20%-80% of cat bites becoming infected. The leading pathogens are Pasturella species, (specifically P. multocida
and P. septica), Streptococcus species, Staphylococcus species, and anaerobes.

Lastly, it is estimated that 10%-15% of human bites become infected. The most common pathogens are Streptococcus species, Staphylococcus aureus, Eikenella corrodens, Corynebacterium, and anaerobes (e.g., Bacteroides, Porphyromonas, and Prevotella species).

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

A wound culture and Gram stain should be obtained only for bites that are suspicious for infection (anaerobic and aerobic cultures with extended incubation times). It is helpful to indicate to the laboratory that the sample is from an animal or human bite and may contain fastidious organisms. Culture and Gram stain of uninfected wounds is not recommended.

For cases of systemic illness, a complete blood count, C-reactive protein level, and erythrocyte sedimentation rate are appropriate. These markers may also be useful in following the disease course for septic arthritis and osteomyelitis. In addition, a blood culture for patients with signs of systemic illness or patients who are immunocompromised is indicated.

Would imaging studies be helpful? If so, which ones?

Radiographs should be obtained for all clenched-fist injuries as well as dog bites to the head, face, and neck of children and should be considered for any injury in which bone or joint penetration is likely or retained foreign bodies, such as teeth, are suspected. Head computed tomography may also be indicated for young children with dog bites to the scalp and face, as penetrating injuries can lead to meningitis or intracranial abscesses.

Confirming the diagnosis

Bite wound evalution should include a detailed description of the wound (i.e., crushing, laceration, puncture, avulsion, or occlusion), location of the wound, signs of edema or infection, depth of the wound, and any findings on wound exploration. A diagram and/or pictures of the wound should be documented. In addition, evaluate for neurovascular compromise and any changes in range of motion. For closed-fist injuries, the hand should be evaluated in both the fisted and extended positions; the third metacarpophalangeal (MCP) joint is most often injured.

The history of the circumstances surrounding the bite should include time of the bite, identification of the biter (breed if applicable), whether the attack was provoked or unprovoked (actual activity of the victim and biter at the time of the incident), and location/environment. The patient’s medical history should include current medications, allergies, immunizations, chronic disease, splenectomy or functional aslpenia, prothestic joints, and immunosuppression.

If the bite is an animal bite, assess for the risk of rabies. If the animal appears rabid or the animal is not available for observation for 10 days, rabies postexposure prophylaxis may be indicated. Further, if the bite is a human bite, the risk of virus transmission (HIV, hepatitis B, hepatitis C) should be assessed.

If you are able to confirm that the patient has been bitten, what treatment should be initiated?

Wound cleansing should begin with high-pressure irrigation (18-gauge catheter and 20-mL syringe) with normal saline. For wounds in which rabies exposure is suspected, use soap and water or, if available, povidine-iodine solution for wound cleansing. After effective irrigation, debride the wound of any devitalized tissue or foreign material. Puncture wounds should not be irrigated with high pressure or debrided.

Laboratory studies and imaging studies should be performed as above.

All edematous wounds should be elevated.

Wound closure: This is a controversial topic and little evidence-based best practice exists. All facial wounds may be repaired by primary closure after extensive irrigation. Consider consultation with a plastic surgery specialist. Consider primary closure for dog bites less than 8 hours old, except for those involving the hands or feet. Primary closure is not recommended for most other wounds.

Tetanus prophylaxis should be guided by the patient’s immunization history and current guidelines. Bites are not considered clean and minor wounds.

Rabies postexposure prophylaxis: If the animal appears well and can be observed for 10 days, no treatment is indicated. If the animal is rabid or rabies is suspected, begin treatment with immunization and human rabies immune globulin (HRIG). The vaccine should be given intramuscularly (IM)on days 0, 3, 7, and 14. HRIG, 20 IU/kg, should be infiltrated into and around the wound as much as possible. Any remaining immunoglobulin can be given IM in an area separate from the vaccine. If the animal cannot be located, the risk of rabies should be discussed with local public health officials. Please see http://aapredbook.org.

Hepatitis B: Treatment with hepatitis B immune globulin and/or immunization depends on both the victim and the assailant’s immune status. Please see http://aapredbook.org.

HIV: Nonoccupational postexposure prophylaxis—HIV transmission through a human bite is rare and most often occurs if the assailant’s saliva is mixed with blood. However, for incidents in which the assailant is known to be HIV positive or the risk of infection is high and the victim presents within 72 hours, postexposure prophylaxis is warranted. The decision to treat should be done in concert with an infectious disease specialist.

Immobilization: Extremities, and in particular hands, should be splinted in a functional position.

Antibiotics: Antibiotic prophylaxis is a controversial topic and most recommendations are based on expert opinion.

Prophylaxis should be considered for wounds with high risk for infection, such as puncture or crush wounds; cat bites; injuries with deep penetration of bone, tendon, or joint; injury near a prosthetic joint; immunocompromised patients or patients with chronic disease, wounds of the hand, feet, or genitals or any wound repaired with primary closure.

For cat, dog, or human bites, the recommended antibiotic choice is amoxicillin-clavulanate for 3-5 days. Extended-spectrum cephalosporin plus clindamycin (unless there is suspected cephalosporin allergy) or trimethoprim-sulfamethoxazole plus clindamycin may be used for penicillin-allergic patients. Note that greater than 30% of all hand wounds become infected.

Treatment of infected wounds should be intravenous with amoxicillin-clavulanate, ticracillin-clavulanate, or piperacillin-tazobactam. Overall duration of therapy is 10-14 days; however transition to oral therapy can occur once the infection is resolving. For penicillin-allergic patients, use trimethoprim-sulfamethoxazole plus clindamycin or cefoxitin or meropenem. For complicated infections (e.g., septic arthritis, osteomyelitis, tenosynovitis) duration of therapy will be prolonged. Antibiotic choice should be guided by culture results if available.

Consultation: Surgical consultation is recommended for, but not limited to, hand injuries, septic arthritis, injuries with neurovascular compromise, and deep abscesses.

Follow-up care: Wounds should be reassessed within 24-48 hours of discharge. If a child sustains a human bite with an intercanine distance greater than 3 cm, evaluate for child abuse.

What are the possible outcomes of animal and human bites?

Prognosis will be dependent on any sustained loss of function, disfigurement, or sequelae of long-term complications (e.g., osteomyelitis, septic arthritis, tenosynovitis, sepsis).

What causes this disease and how frequent is it?

Approximately one third of American households have dogs and cats as pets, and each year, almost 5 million Americans sustain a bite injury. These injuries account for 1% of all emergency room visits, although 80% of people who sustain bites never seek medical attention. Dog bites account for 80%-90% of the total injuries, followed by cat bites (5%-10%) and human bites (2-3%). In addition, 10-20 deaths occur annually from dog bites, and a majority of these are in the pediatric population.

Dog bites occur more often in the warmer months and in boys more often than in girls. Peak incidence of dog bites is in the 5-9 year old age group. The majority of bites are by an animal known to the child, although approximately 50% are considered unprovoked. Fatal dog attacks have been associated most commonly with pit bulls, rottweilers, and German shepherds, but any breed can attack. Children frequently suffer injuries to the head, neck, and face leading to the potential for significant blood loss. However, cat bites are more commonly found in adult women and tend to be located in the upper extremity or face. These are most often puncture wounds.

Human bites have a male predominance, with a median age of about 28 years. These are often on the hand or fingers and many may be due to clenched-fist injuries when one individual’s fist comes into contact with another individual’s teeth. Human bites are a leading cause of injury in day care centers in the United States, although the dermis is usually not penetrated and injury is minor.

It is estimated that annual costs related to animal bites is approximately $30 million; however this may be a gross underestimation, as other reports suggest that direct health care costs for dog bites alone exceed $100 million each year.

What complications might you expect from bites or treatment of the bite?

Both animal and human bites can result in infection, loss of function, and disfigurement. More common infections include regional lymphadenopathy, lymphangitis or local abcesses, bacteremia, tenosynovitis, septic arthritis, and osteomyelitis. Less common or rare sequelae include sepsis, meningitis, endocarditis, and brain abcesses. There have been reports of death secondary to C. canimorus
in patients with liver disease or asplenia.

Specifically, human bites related to closed-fist injury and, in particular infection of the MCP joint, may lead to amputation or loss of function. Rarely, human bites can lead to transimission of hepatitis B virus, hepatitis C virus, syphilis, HIV, and herpes simplex virus. Cat bites have been associated with tularemia and cat scratch disease (Bartonella henselae). Further, dog bites can lead to death secondary to exsanguination, most often in children. Children should be evaluated for posttraumatic stress disorder after a dog bite that required at least minor wound repair.

How can animal and human bites be prevented?

One of the most important things to remember is that no child should be left unattended with an animal. Although statistics have been reported regarding the propensity of certain dog breeds to bite, as well as the circumstances surrounding those bites, the data are insufficient to truly know who will bite and when. Data related to the bite (e.g., dog breed, situation surrounding the bite, provocation, or specific definition of provation) are not often well documented. Further, most animal bites, dog and cat, are from animals known to the child, and these bites frequently occur in the home.

A plethora of helpful recommendations exist for dog bite prevention, although evaluation for impact or effectiveness of the recommendations is wanting. Helpful suggestions include the following:

Provide supervision of children with family pets.

Do not interact with the pet when the animal is eating, sleeping, or caring for its young.

Avoid running from dogs or engaging in excitable games such as tug of war.

Ensure the pet is comfortable around people and other animials (socialization).

Allow the animal to sniff you before touching it.

Children should be advised not to kiss their pets or approach strange animals.

Neuter the pet.

Use a leash when in public.

What is the evidence?

Thomas, N, Brook, I. “Animal bite-associated infections: microbiology and treatment”. Expert Rev Anti Infect Ther. vol. 9. 2011. pp. 215-26.

Patronek, GJ, Slavinski, SA. “Animal bites”. J Am Vet Med Assoc. vol. 234. 2009. pp. 336-45.

Fleisher, GR. “The managrment of bite wounds”. N Engl J Med. vol. 340. 1999. pp. 138-40.

Looke, D, Dendle, C. “Bites (Mammalian)”. Clin Evid (Online).. vol. 7. 2010. pp. 1-5.

Brook, I. “Microbiology and management of human and animal bite wound infections”. Prim Care. vol. 30. 2003. pp. 25-39.

Kannikeswaran, N, Kamat, D. “Mammalian bites”. Clin Pediatr (Phila). vol. 48. 2009. pp. 145-8.

Garcia, VF. “Animal bites and infections”. Pediatr Rev. vol. 18. 1997. pp. 127-30.

Wiley, JF. “Mammalian bites. Review of evaluation and management”. Clin Pediatr (Phila). vol. 29. 1990. pp. 283-7.

Dendle, C, Looke, D. “Review article: animal bites: an update for management with a focus on infections”. Emerg Med Australas. vol. 20. 2008. pp. 458-67.

Morgan, M. “Hospital managment of animal and human bites”. J Hosp Infect. vol. 61. 2005. pp. 1-10.

Patil, PD, Panchabhai, TS, Galwankar, SC. “Managing human bites”. J Emerg Trauma Shock. vol. 2. 2009. pp. 186-90.

Daniels, DM, Ritzi, RBS, O’Neil, J. “Analysis of nonfatal dog bites in children”. J Trauma. vol. 66. 2009. pp. S17-22.

Broder, J, Jerrard, D, Olshaker, J. “Low risk of infection in selected human bites treated without antibiotics”. Am J Emerg Med. vol. 22. 2004. pp. 10-3.

Pickering, LK, Baker, CJ, Long, SS. “American Academy of Pediatrics. Bite wounds”. 2006. pp. 187-91.

Pickering, LK, Baker, CJ, Long, SS. “American Academy of Pediatrics. Hepatitis B”. 2006. pp. 337-56.

Pickering, LK, Baker, CJ, Long, SS. “American Academy of Pediatrics. Human Immunodeficieny virus infection”. 2006. pp. 380a-400a.

Pickering, LK, Baker, CJ, Long, SS. “American Academy of Pediatrics. Rabies”. 2006. pp. 552-9.

Mandell, GL, Bennett, JE, Dolin, R. “Principles and Practice of Infectious Disease”. 2010.

Behrman, RE, Kliegman, RM, Jenson, HB. “Nelson Textbook of Pediatrics”. 2004.

Zaoutis, LB, Chiang, VW. “Comprehensive Pediatric Hospital Medicine”. 2007.

Bronstein, AC, Spyker, DA, Cantilena, LR. “2009 Annual Report of the American Association of Poison Control Centers' National Poison Data System (NPDS): 27th Annual Report”. Clin Toxicol (Phila). vol. 48. 2010. pp. 979-1178.

Bronstein, AC, Spyker, DA, Cantilena, LR. “2008 Annual Report of the American Association of Poison Control Centers' National Poison Data System (NPDS): 26th Annual Report”. Clin Toxicol (Philia). vol. 47. 2009. pp. 911-1084.

Bronstein, AC, Spyker, DA, Cantilena, LR. “2001 Annual Report of the American Association of Poison Control Centers' National Poison Data System (NPDS): 25th Annual Report”. Clin Toxicol (Phila). vol. 46. 2008. pp. 927-1057.

Ongoing controversies regarding etiology, diagnosis, treatment

Because of a paucity of double-blind randomized controlled trials regarding primary versus delayed versus secondary wound closure in both animal and human bites, controversy exists, and most recommendations are based on small studies or expert opinion. The same is true regarding the use of antibiotic prophylaxis for animal and human bites.