Special Feature
Management of Dog and Cat Bites
By Louis M. Bell, MD, FAAP
Millions of americans own pets. thirty-five percent of American households owned a dog in 1994, making the U.S. dog population more than 50 million.1 Millions more U.S. households have cats as pets. Unfortunately, dogs and cats may bite. The Centers for Disease Control and Prevention (CDC) estimate that approximately 4.5 million bites occur annually, of which 800,000 are serious enough to require medical attention.2 Children are most at risk for serious injury or death from bite wounds. Not only do bites to children represent more than 50% of total cases, 26% of dog bites in children require medical attention compared to only 12% in adults.3 Furthermore, more than 55% of the bite-related fatalities occur in children younger than 10 years.4
Appropriate management and choice of antibiotics for dog and cat bites require knowledge of the epidemiology and bacteriology of infected bites. A recent study by Talan and associates5 and the accompanying commentary by Fleisher6 provide excellent information upon which decisions about prophylaxis and/or treatment can be based. In the study, the bacteriology of infected wounds from 50 persons with dog bites and 57 patients with cat bites at 18 university-affiliated emergency departments were prospectively collected from April 1994 through December 1995. The patients enrolled in this multicentered study ranged in age from 1 to 82 years, with a mean age of 33 years. Twenty-two percent of patients were younger than 18 years of age and five were younger than 3 years. Most patients were seen 1-2 days after the bite.
A mean of five bacteria were recovered from the bite wounds. Many wounds grew mixed aerobic and anaerobic pathogens. As expected, Pasteurella species was the most common bacteria isolated; 50% were from dog bites and 75% from cat bites. Staphylococcus aureus was isolated in 20% of dog bites and 4% of cat bites, somewhat lower than in previous reports. Anaerobic bacteria were recovered as the lone pathogen from only one dog bite wound.
Immediate Management of Bite Wounds
When possible, the wound should be cleaned immediately with soap and water. If the victim is brought immediately for outpatient evaluation, further decontamination and careful wound exploration is warranted. Sixty percent of dog bites and 85% of cat bites in Talan et al’s study were puncture wounds. Small, apparently insignificant puncture wounds may overlie fractured skulls, lacerated tendons, or neurovascular damage. Copious amounts of fluid under pressure should be used to clean these puncture wounds. Conscious sedation may be required to perform these tasks adequately.
Obviously, not all bite victims think to seek immediate medical attention and may wait until there is pain and signs of infection. In Talan et al’s study, those with infected cat bites presented significantly sooner, at a mean of 23 hours, as opposed to 35 hours for those with dog bites. Others studied have noted the increased risk associated with cat bites, which tend to be puncture wounds resulting from the cat’s long and slender teeth.7
After careful exploration and cleaning, one should decide whether to primarily close the wound. If the wound is a superficial laceration in an area where cosmetic appearance is important, closure should be considered. In general, puncture wounds, human bites, and wounds more than 12-24 hours old, depending on the location (shorter time for extremities, longer time for facial lacerations), should not be closed primarily.
The risk of infection after a bite is estimated to be 5-15%.7 Therefore, prophylactic antibiotics, although controversial, should be considered. I personally prescribe a beta-lactam antibiotic and a beta-lactamase inhibitor combination for any wounds that can’t be adequately irrigated (e.g., puncture wounds), bites to the hands or feet where infection may develop and track along tendon sheath leading to serious morbidity, or wounds that require surgical repair. One should consider prophylactic antibiotics for virtually all cat bites because 85% of these bites are puncture wounds. Prophylaxis for 3-5 days seems appropriate.
All animal bites should be considered tetanus-prone wounds. Therefore, if the patient’s immune status is unknown or if there have been fewer than three doses of tetanus toxoid, tetanus toxoid and tetanus immune globulin should be given. Tetanus toxoid alone should be given to those who have received a primary immunization series (3 immunizations) but have not had a booster for five years. It is recommended that children younger than 7 years should be given DTaP. For persons older than 7 years, the tetanus toxoid should be in the form of Td (adult use tetanus and diphtheria toxoid).8
Although rabies is rare, 32 people were diagnosed with rabies in the United States from 1980 to 1996.9 Furthermore, in 1988, cats became the most commonly reported domestic animal found to be rabid in the United States. Therefore, the need for rabies prophylaxis should be accessed following animal bites. Following the biting episode, a healthy appearing dog and cat can be observed for 10 days. If illness or odd behavior is noted during that time, then the animal should be killed and the brain examined for signs of rabies.
If rabies prophylaxis is indicated, human diploid cell vaccine (HCDV) should be given in the deltoid area on the first day of treatment and then days 3, 7, 14, and 28. Vaccine administration in the gluteal muscle is acceptable in infants. In addition to active immunization, passive immunization with human rabies immune globulin (20 IU/kg of body weight) should be given on the first day of treatment. As much of the dose as possible should be infiltrated in the area of the wound, with the remainder at a site distal to the site where the HCDV was given.
Finally, in Talan et al’s study, infections become symptomatic enough to lead to an emergency department visit 18-50 hours after the bite. Therefore, a follow-up visit or phone call within the first 1-2 days after the injury is important.
Treatment of Infected Bite Wounds
If infection ensues, the value of Talan et al’s detailed bacteriologic analysis is clear when one is required to choose presumptive antibiotics to care for a child or adult with an infected animal bite. Presumptive antibiotics for infected animal bite wounds should include coverage for both aerobes (Pasteurella species, Streptococci species, and Staphylococcus species) and anaerobes.
First-generation cephalosporins may fail, especially if Pasteurella is involved. Therefore, reasonable therapy should include a combination of a beta-lactam antibiotic and beta-lactamase inhibitor. Penicillin (for anaerobes and Pasteurella), in combination with a first-generation cephalosporin or a semisynthetic penicillinase-resistant penicillin such as oxacillin, is also acceptable. Length of therapy will depend on the severity of infection but is usually in the range of 7-14 days.
The Immunocompromised Child
Although bite wounds may result in localized cellulitis, occasionally more serious systemic infections develop, such as meningitis, endocarditis, and septic shock. For example, patients without spleens are particularly susceptible to severe and sometimes fatal sepsis with Capnocytophaga canimorsus (also called DF-2),10 an organism found in the mouth flora of dogs and in 4.7% of infected wounds in Talan et al’s report. Therefore, splenectomized patients and those with defective splenic function should take special care in handling domestic pets to avoid even trivial bites or scratches and should probably receive prophylactic antibiotics.
Other Human Zoonotic Infections
The focus of this article has been the acute management of bite wounds and treatment of dog and cat bite infections. However, it is important to remember that other bacterial, rickettsial, parasitic, and fungal infections may be transmitted by dogs and cats.11
Bacterial diseases, such as cat-scratch disease (etiology Bartonella henselae), cause tender regional lymphadenopathy after inoculation. Brucellosis is generally a disease of domestic animals (etiology Brucella abortus, B. melitensis, B. suis). However, rural dogs may serve as a reservoir of human and livestock infection. Both dogs and cats carry Campylobacter and Salmonella (both common causes of human bacterial diarrhea). Dogs may transmit the spirochete Leptospira interrogans. The organism survives in the distal renal tubules of dogs, resulting in urine that may remain contagious for life.
Cats are both the definitive and intermediate hosts for the parasite Toxoplasma gondii. In older patients, infection follows ingestion of cysts on substances contaminated with cat feces, raw or undercooked meats, or exposure to contaminated soil. In children and adults, this infection may be asymptomatic or cause a self-limited mononucleosis-like syndrome. However, toxoplasmosis infection during pregnancy may result in transmission to the fetus and severe congenital infection with long-term morbidity.
References
1. Wise JK, Yang JJ. Dog and cat ownership, 1991-1998. J Am Vet Med Assoc 1994;204:1166-1167.
2. Blackman JR. Man’s best friend? J Am Board Fam Pract 1998;11:167-169.
3. Sacks JJ, et al. Fatal dog attacks, 1989-1994. Pediatrics 1996;97:891-895.
4. Weiss HB, et al. Incidence of dog bite injuries treated in emergency departments. JAMA 1998;279:51-53.
5. Talan DA, et al. Bacteriologic analysis of infected dog and cat bites. N Engl J Med 1999;340:85-92.
6. Fleisher GR. The management of bite wounds. N Engl J Med 1999;340:138-140.
7. Dive DJ. Cat bite wounds: Risk factors for infection. Ann Emerg Med 1991;20:973-979.
8. Peter G, ed. Redbook: Report of the Committee on Infectious Diseases, 1997 tetanus. Elk Grove Village, IL: American Academy of Pediatrics; 1997:518-523.
9. Noah DL, et al. Epidemiology of human rabies in the United States, 1980 to 1996. Ann Intern Med 1998; 128:922-930.
10. Westwell AJ, et al. DF-2 infection. BMJ 1989; 298:116-117.
11. Tan JS. Human zoonotic infections transmitted by dogs and cats. Arch Intern Med 1997;157:1933-1943.
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