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A 35-year-old male veterinarian was bitten by a healthy 2-year-old male Chow Chow while trimming its nails. Wounds on the right wrist and hand were cleansed with povidone-iodine solution and a sterile bandage was applied. Twelve hours later, the man complained of increasing discomfort at the bite site. Twenty-four hours after the injury, he was taken to an emergency room because of malaise, chills, and localized pain.

On physical examination, oral temperature was 38.3 C; blood pressure was 116/80 mm of Hg; pulse rate was 85 beats/min; and respiratory rate was 18 breaths/min. Puncture wounds were observed on the anterior and posterior aspects of the right hand and wrist, which were swollen and erythematous. A serosanguinous exudate drained from the wounds.

Because constitutional signs were evident and the wounds were infected, the veterinarian was admitted to the hospital and was referred to a hand surgeon. A CBC revealed leukocytosis, but bacteria were not observed in neutrophils in Wright-stained blood smears or in gram-stained buffy coat smears. Stained smears of wound exudates had many gram-negative coccobacillary organisms and many gram-negative rods. Bacterial culture of the exudates yielded a profuse growth of Pasteurella multocida, Fusobacterium sp, and Bacteroides sp.

Penicillin was administered IV. The bite wounds were irrigated, debrided of devitalized tissues, and covered with gauze impregnated with an antibacterial agent. The affected hand was wrapped in a bulky mitten dressing and was elevated. Five days later, the patient's discomfort had ceased. Erythema and swelling at the bite sites had receded markedly, and no exudation was evident. The margins of the larger puncture wounds on the wrists were debrided and sutured, and the dressing was reapplied. Antimicrobial treatment was changed to oral administration of amoxicillin with clavulanic acid. The veterinarian was discharged from the hospital on day 6 and recovered without complications.

The patient directed the following questions to his attending surgeon^a:

Q: How many people are bitten by dogs and cats each year?

A: Health authorities report that more than 1 million people are bitten by dogs each year¹; however, it is estimated that only half of all bites are reported.² In spite of the fact that most dog bite wounds are trivial and most victims do not seek medical attention, 3 bite wounds account for about 1% of all emergency room admissions and cost approximately $30 million in annual health care.⁴

Surveys of schoolchildren have shown that the frequency of dog bites may be much higher than indicated by reports from health authorities.⁵ Fifty-five percent of boys and 39 percent of girls, from 4 to 18 years old, reported being bitten during their lifetimes. Seventeen percent of children reported receiving medical attention for dog bites during their lifetimes. The investigators concluded that being bitten by a dog is a rather common occurrence in children between the ages of 7 and 12 years, and that the event is greatly underestimated by official bite statistics. In a survey of veterinarians from Minnesota and Wisconsin, 92.3% of respondents reported being bitten by dogs, and 81% reported being bitten by cats.⁶

Q: Are any groups at risk for being bitten by dogs or cats?

A: One half to two thirds of dog bite victims are less than 20 years old, with many victims being less than 10 years old. Injuries may be more severe in the latter group.⁷ Men and boys are bitten more often than women and girls, as the former group is more likely to own dogs as pets and to come into close contact with unleashed free-roaming dogs.²

Dog bites occur more commonly in the warmer months when there is a greater opportunity for outdoor contact between human beings and pets. The incidence begins to increase in March, and peaks between June and August. Most dog bites occur in the afternoon and evening, with the peak between 3 PM and 7 PM.² Recreational activities such as jogging or cycling that are pursued during these times tend to provoke dogs to attack.

Q: Which dogs bite people?

A: About half of all bites are from dogs owned by neighbors.(5) Pets of the victim's family or pets of friends often are involved.⁸ Most bites are from large or medium-sized dogs that are being kept for protection in urban areas.² Overall, dogs inflict 80 to 90% of the animal bites that require medical attention.⁹

Q: On which part of the body do most victims get bitten?

A: Most victims are bitten on their arms and hands.^3,4,10 The right arm is most often bitten, as many victims attempt to protect themselves with this limb.² Bites from family dogs are more prevalent on the arm and back, compared with bites from stray dogs and dogs of unknown background that are more likely to be inflicted on the leg.¹¹ About 65% of facial bites are in children less than 10 years of age.²

Q: Which bacteria cause most bite wound infections?

A: Aerobic flora of the skin of the victim and aerobic and anaerobic oral flora of the biting animal are all capable of inducing infection,^7,9 with the oral flora being more important pathogenically.¹² Most infected bite wounds contain several species of aerobic and anaerobic bacteria that interact synergistically to make elimination more difficult. There is a larger mean number (5.4) of bacterial isolates from infected human bites than from infected animal bites (2.8).⁹

More than 64 species of bacteria may be found in the mouths of dogs.¹³ The normal oral flora of dogs includes P multocida, Staphylococcus aureus, S epidermidis, S saprophyticus, Streptococcus sp, Neisseria sp, Moraxella sp, Escherichia coli, Enterobacter aero-genes, Pseudomonas fluorescens, Acinetobacter calcoa-ceticus, Corynebacterium sp, Actinomyces sp, Bacillus sp, Caryophanon sp, Mycoplasma sp, and the alphanumeric strains IIj, EF-4, M-5, and DF-2.^8,14,15 The oral flora of cats is similar.⁸

The species of bacteria isolated from clinically noninfected and infected animal bite wounds are similar.^3,12 In one study, aerobic bacteria alone were isolated from 24% of animal bite wounds, anaerobic bacteria alone from 10%, and mixed isolates from 66%.⁹ In another study, aerobic bacteria were isolated from 74% of all animal bite wounds, and anaerobic bacteria were isolated from 41% of wounds.³ The most common aerobic isolate was alpha-hemolytic Streptococcus sp. Bacteroides sp and Fusobacterium sp were the most common anaerobic isolates.

Infections with S aureus often develop as a sequela to self-debridement.¹ Seventy-seven percent of veterinarians reported that they treated themselves after being injured in some manner during their work: 19.7% reported that they sutured their own wounds, and 67.5% reported that they prescribed antimicrobial agents for themselves.⁶

Q: What role does P multocida play in animal bite wounds?

A: Pasteurella multocida is a nonmotile, pleomorphic, gram-negative coccobacillus.^16,17 The organism may be responsible for up to 50 and 90% of infections resulting from dog bite wounds and cat bite wounds, respectively,¹⁸ and is the most common isolate from victims hospitalized with infected bites.⁸ Recently, it has been proposed that the species Pasteurella includes the following: (1) P canis, which is found in the oral cavity of dogs and often is isolated from persons with infected dog bites; (2) P dagmatis, which may be isolated from the oral cavity of dogs and cats and may cause local and systemic infections in people bitten by animals; (3) P stomatis, which may be isolated from the respiratory tracts of dogs and cats; and (4) P multocida, which may be isolated from a variety of mammalian species.¹⁹

Pasteurella spp were isolated from the tonsillar crypts of 92 and 99% of dogs and cats, respectively.²⁰ Pasteurella canis was isolated from 20 and 27% of dogs and cats, respectively. The risks of wound infection with P multocida are estimated to be 10 times higher after cat bites than after dog bites.²¹ Cat bite wounds usually are composed of small deep puncture wounds that are difficult to irrigate and debride. In addition, the Pasteurella sp isolated from cats, compared with that isolated from dogs, appear to be more pathogenic to mice, and this characteristic may result in more aggressive wound infections in people bitten by cats.²⁰

Most human infections with P multocida result from direct inoculation of the organism into a bite wound. In 29% of people with bone and joint P multocida infections, there was no history of scratches or bites, yet there was a record of exposure to animals; in 17%, there was no history of exposure to animals.¹⁷

Pasteurella multocida may cause a rapidly developing cellulitis characterized by erythema, pain, and swelling, which often develops within 2 days of injury.^10,22 A serosanguinous or gray malodorous exudate may develop. The organism may be responsible for low-grade chronic cellulitis and delayed wound healing after bite wounds.²² Human respiratory tract infections may result from colonization with P multocida acquired from the nasopharyngeal flora of animals.¹⁶

Complications of bite wounds infected with P multocida include tenosynovitis, septic arthritis, osteomyelitis, abscesses, and fatal sepsis.^17,23 Chronic complications of P multocida infections are more likely to develop in people with underlying diseases or defective defense mechanisms. Septic arthritis usually affects joints that were previously diseased. Bacteremia is more likely to develop in people taking corticosteroids or who suffer from alcoholic liver disease. Bronchopneumonia caused by P multocida usually develops in people with other underlying respiratory diseases.¹⁷

Q: Which bite wounds become infected?

A: Wound infection most likely develops:

• When the victim is more than 50 years old.²²
  
  
• When puncture wounds preclude thorough cleansing.²²
  
  
• When the bites are on the hands. Infection occurred in 28% of hand wounds, compared with 4% of bites on the face.⁹
  
  
• When there is a delay of more than 24 hours in seeking treatment.^9,22
  
  
• When inadequate attention is paid to careful irrigation and debridement during initial wound management.²²

Q: From which bite wounds should specimens be taken for bacteriologic culturing?

A: Presently, it is considered unnecessary to obtain specimens from wounds with no clinical signs of infection^{1,7,13,22,24,25}; however, specimens should be obtained in the following instances:

• When bite wounds are accompanied by overt signs of local infection.
  
  
• When bite wounds are undergoing rapid deterioration.
  
  
• When bite wounds are accompanied by constitutional signs.
  
  
• When bite wounds do not respond to empirical antimicrobial treatment.
  
  
• When immunocompromised people are bitten.²⁶

Gram-stained smears from noninfected wounds may provide inexpensive and timely information about the presence of potential pathogens,¹³ and may be used to help select initial antimicrobial treatment while cultures are pending.⁷

Q: What are the general principles of bite wound management?

A: Fortunately, about half of all bite wounds are trivial; however, at least 10% require suturing, and 1 to 2% of bite victims must be hospitalized.⁹

Wounds should first be examined for signs of infection, even though these signs are rarely visible within 8 hours of injury.³ The injured area should be evaluated for evidence of integrity of vascular tissues and motor and neurologic function.¹ The wound should be explored carefully for signs of damage to tendons, fascia, joint capsules, cartilage, and bone. When infection is evident, the physician may trace the extent of cellulitis on the skin with a marking pen to monitor response to treatment. In deteriorating wounds, cellulitis usually spreads proximally.¹ Regional lymph nodes should be evaluated for evidence of lymphadenopathy or lymphangitis.

Emergency room physicians are aware that puncture wounds are deceptive and are often more extensive than recognized on initial examination.¹ Radiographs may be obtained when deep puncture wounds are close to bone or joints. These radiographs may be used as baseline data in case osteomyelitis or septic arthritis develop.⁴

Many dog bites cause crushing injuries and avulsion of tissues rather than puncture wounds or lacerations.¹³ Dogs' jaws may exert a pressure of 200 to 450 lbs psi during a bite.²⁷ The injured area may be swollen and painful and may contain much devitalized tissue, predisposing to infection.¹

The management of bite wounds depends on⁴:

• Where the wound is located.
  
  
• Whether the victim is examined before or after 8 hours have elapsed from the time of injury.
  
  
• Whether the wound is clean or infected.
  
  
• What pathogens are involved, and what antimicrobial agents are effective against them.

Physicians agree that all bite wounds require meticulous cleansing, high-pressure irrigation, and careful debridement.²⁸ Povidone-iodine solution is preferred for initial wound cleansing. The solution does not contain detergents found in some other preparations that may induce pain, may delay wound healing, and may further damage delicate, exposed subcutaneous tissues. The wounds may be cleansed gently with fine mesh sponges²⁸; vigorous scrubbing may devitalize tissue and delay healing.⁷

The rabies immunization history of the biting animal and the rabies and tetanus immunization histories of the victim are determined.^1,7,29

Q: Why is wound irrigation so important?

A: Irrigation decreases the number of potentially pathogenic bacteria that were inoculated during the bite. In one study, infection developed in 69% of wounds that were not irrigated, compared with an infection rate of 12% in wounds that were irrigated thoroughly.²² Irrigation is especially important in hand wounds, where the depth of wound, presence of vital structures, and tightness of the skin prevent adequate wound debridement.¹³

After the wounds have been cleansed with povidone-iodine solution, they are irrigated under pressure with normal saline (0.9% NaCl) solution, using an 18-gauge blunted needle on a 35 ml syringe.²⁸ Up to a liter of saline solution may be used at a pressure of 50 to 70 psi.⁷

Q: Why is wound debridement so important?

A: Removal of devitalized tissue and skin tags appears to decrease the risk of infection in bite wounds. In one study, infection developed in 17% of wounds that had not been debrided, compared with an infection rate of 7.1 % in debrided wounds.²² In addition, debridement allows easier surgical repair and results in a smaller scar at the site of injury.¹³ Although debridement of tear wounds is generally accepted, the need to debride puncture wounds remains controversial.¹

Q: Which bite wounds should be sutured?

A: Opinions differ on this question. In the past, it was considered unwise to close any dog bite wound; however, more physicians now are performing primary closure after meticulous surgical wound cleansing.¹³

The decision to perform primary wound closure depends on⁷:

• Whether the wound will close satisfactorily on its own.
  
  
• The risk of infection in that bite wound.
  
  
• Whether there are cosmetic considerations.

Fresh noninfected wounds may be sutured after wound cleansing, irrigation, and debridement. After initial wound management, small infected wounds may be allowed to heal by secondary intention if they are in cosmetically unimportant areas. Larger wounds may be closed by primary intention after infection has resolved.²⁸

Deep puncture wounds caused by cat bites usually are not sutured because of the high prevalence of subsequent infections.²⁸

Q: Which animal bite wound victims require referral to a specialist or hospitalization?

A: Emergency room physicians may determine that certain patients with bite wounds should be referred to a surgeon for further evaluation or should be hospitalized. These may include²⁸:

• People with hand bites, except those bites that are superficial and fresh.
  
  
• People with extensive infection in the bite site.
  
  
• People with bites in which there is damage to tendon, cartilage, bone, and joint capsule.
  
  
• People with disfigurement or tissue loss requiring cosmetic surgery.
  
  
• People, especially those with hand injuries, who are predicted to comply poorly with the emergency room physician's recommendations.
  
  
• Young children with head injuries from bites inflicted by large dogs.²¹ The severity of injury may be underestimated based on examination of the scalp wounds.

Q: Which bite victims should receive antimicrobials?

A: Antimicrobial treatment has been recommended for the following groups of bite victims²⁸:

• People bitten by cats.
  
  
• People who seek treatment 8 hours or more after being bitten by a dog.
  
  
• People whose bite wounds were sutured and who are being evaluated for potential delayed wound closure.
  
  
• People with bite wounds on the hands.
  
  
• People with deep puncture wounds that were not amenable to thorough irrigation and debridement.
  
  
• People who are diabetic or who are immunocompromised.
  
  
• People with facial bites.⁹

Q: Should antimicrobial treatment be prescribed for people with noninfected bite wounds?

A: This question, more than any other issue, remains a controversial subject in animal bite wound management. Many authors use the term prophylactic antimicrobial treatment in this situation, insinuating that treatment may prevent infection later. Others state that this definition is incorrect in that treatment is not being started before the bite wound is received.⁷ Many bite wounds that are not accompanied by signs of infection are contaminated by bacteria that are potentially pathogenic.

Several investigators have reported that antimicrobial treatment does not decrease the prevalence of infection in dog bite victims with clinically noninfected wounds who were treated with proper wound cleansing.^22,25,30,31 Prophylactic administration of antimicrobials may not be indicated in these people as long as thorough wound care is achieved. As noted previously, this observation does not apply to people who are at risk for developing infection for victims of cat bites, or for bites on the hands and face.

Some physicians recommend antimicrobial treatment for clinically noninfected dog bites, noting that these wounds may be contaminated with aerobic and anaerobic bacteria that may be capable of causing infection. In addition, it may be difficult to predict which wounds are likely to become clinically infected.¹ Other physicians prescribe antimicrobial treatment for all dog bite victims, except those who seek medical attention 24 hours or more after injury and who have no signs of infection.³

Further studies are needed to resolve the question of whether antimicrobial treatment is indicated in clinically noninfected dog bite wounds. Presently the preferred antimicrobials for prophylactic treatment are a combination of a penicillin and a penicillinase- resistant penicillin, or amoxicillin with clavulanic acid.¹⁸

Q: Which antimicrobial agents are most commonly used for infected bite wounds?

A: There is no single antimicrobial agent that is effective against all of the aerobic and anaerobic bacteria that may be inoculated into bite wounds.²³ Pasteurella multocida usually is resistant to the penicillinase-resistant penicillins, yet is sensitive to penicillin.⁹ Cephalosporins administered orally do not reach blood concentrations high enough to eradicate P multocida infections reliably.¹⁷ Staphylococcus aureus usually is resistant to penicillin.⁹

For people with infected bite wounds, penicillin is recommended as the initial choice for parenteral treatment.³ If gram-stained smears from wound exudates indicate there may be coinfection with S aureus, a penicillinase-resistant penicillin may be added. A combination of ticarcillin with clavulanic acid has been recommended for initial parenteral treatment. Ultimately, antimicrobial agents are chosen based on the results of bacterial culture and antimicrobial susceptibility, and on observation of response to treatment.⁸

Bite wound victims treated as outpatients may be advised to return for reevaluation after 48 hours by which time, signs of infection may have arisen. At this time, treatment may be modified based on the results of bacterial culture and susceptibility and sutures may be removed if signs of infection are evident.²⁸ Patients who have suffered deep cat bites are evaluated carefully to allow early detection of complications such as osteomyelitis.¹⁷

Footnote

(a) The following questions and answers posed to a physician are offered to JAVMA readers for their own information, but are not intended as a source of information from which a veterinarian would offer advice on human medical matters.

References

1. Rest JG, Goldstein EJC. Management of human and animal bite wounds. Emerg Med Clin North Am 1985; 3:117-126.

2. Harris D, Imperato PJ, Oken B. Dog bites--an unrecognized epidemic. Bull NY Acad Med 1974; 50:981-1000.

3. Goldstein EJC, Citron DM, Finegold SM. Dog bite wounds and infection: a prospective clinical study. Ann Emerg Med 1980; 9:508-512.

4. Goldstein EJC, Richwald GA. Human and animal bite wounds. Am Fam Physician 1987; 36:101-109.

5. Beck AM, Jones BA. Unreported dog bites in children. Public Health Rep 1985; 100:315-321.

6. Landercasper J, Cogbill TH, Strutt PJ, et al. Trauma and the veterinarian. J Trauma 1988; 28:1-4.

7. Underman AE. Bite wounds inflicted by dogs and cats. Vet Clin North Am [Small Anim Pract] 1987; 17:195-207.

8. Feder HM, Shanley JD, Barbera JA. Review of 59 patients hospitalized with animal bites. Pediatr Infect Dis J 1987; 6:24-28.

9. Brook I. Microbiology of human and animal bite wounds. Pediatr Infect Dis J 1987; 6:29-32.

10. Thomas PR, Buntine JA. Man's best friend?: a review of the Austin Hospital's experience with dog bites. Med J Aust 1987; 147:536-540.

11. Ordog GJ, Dog bite wound factors (letter). Ann Emerg Med 1987; 16:724-725.

12. Goldstein EJC, Citron DM, Wield B, et al. Bacteriology of human and animal bite wounds. J Clin Microbiol 1978; 8:667-672.

13. Callaham M. Dog bite wounds. JAMA 1980; 144:2327--2328.

14. Bailie WE, Stowe EC, Schmitt AM. Aerobic bacterial flora of oral and nasal fluids of canines with reference to bacteria associated with bites. J Clin Microbiol 1978; 7:223-231.

15. Saphir DA, Carter GR. Gingival flora of the dog with special reference to bacteria associated with bites. J Clin Microbiol 1976; 3:344-349.

16. Jones AGH, Lockton JA. Fatal Pasteurella multocida septicemia following a cat bite in a man without liver disease. J Infect 1987; 15:229-235.

17. Weber DJ, Wolfson JS, Swartz MN, et al. Pasteurella multocida infections. Report of 34 cases and review of the literature. Medicine 1984; 63:133-154.

18. Guertler AT. Antibiotic treatments for hand injuries (letter). Am J Emerg Med 1988; 6:205-206.

19. Mutters R, Ihar P, Pohl S, et al. Reclassification of the genus Pasteurella Trevisan 1887 on the basis of deoxyribonucleic acid homology, with proposals for the new species Pasteurella dagmatis, Pasteurella canis, Pasteurella stomatis, Pasteurella anatis, and Pasteurella langaa. Int J Syst Bacteriol 1985; 35:309-322.

20. Baldrias L, Frost AJ, O'Boyle D. The isolation of Pasteurella-like organisms from the tonsillar region of dogs and cats. J Small Anim Pract 1988; 29:63-68.

21. Steinbok P, Flodmark O, Scheifele DW. Animal bites causing central nervous system injury in children. A report of three cases. Pediatr Neurosci 1985-1986; 12:96-100.

22. Callaham ML. Treatment of common dog bites: infection risk factors. J Am Coll Emerg Phys 1978; 7:83-87.

23. Goldstein EJC, Citron DM, Vagvolgyi AE, et al. Susceptibility of bite wound bacteria to seven oral antimicrobial agents, including RU-985, a new erythromycin: considerations in choosing empiric therapy Antimicrob Agents Chemother 1986; 29:556-559.

24. Spencer RC, Matta H, Ferguson DG, et al. Routine culture of dog bites. Ann Emerg Med 1987; 16:730.

25. Ordog GJ. The bacteriology of dog bite wounds on initial presentation. Ann Emerg Med 1986; 15:1324-1329.

26. Auerbach PS, Morris JA. Acinetobacter calcoaceticus infection following a dog bite. Am J Emerg Med 1987; 5:363-366.

27. Chambers GH, Payne JF. Treatment of dog bite wounds. Minn Med 1969; 52:427-430.

28. Trott A. Care of mammalian bites. Pediatr Infect Dis J 1987; 6:8-10.

29. Perry BD. Rabies. Vet Clin North Am [Small Anim Pract] 1987; 17:73-89.

30. Jones DA, Stanbridge TN. A clinical trial using co-trimoxazole in an attempt to reduce wound infection rates in dog bite wounds. Postgrad Med J 1985; 61:593-594.

31. Rosen RA. The use of antibiotics in the initial management of dog-bite wounds. Am J Emerg Med 1985; 3:19-23.