Bites, Animal & Human

Key Features

Essentials of Diagnosis

• Cat and human bites are more likely to become infected than dog bites

• Bites to the hand are of special concern because of the possibility of closed-space infection

• Antibiotic prophylaxis indicated for noninfected bites of the hand; hospitalization required for infected hand bites

• All infected wounds need to be cultured to direct therapy

General Considerations

• Biting animals are usually known by their victims, and most biting incidents are provoked (ie, bites occur while playing with the animal or waking it abruptly from sleep)

• Important determinants of whether bites become infected

  • Animal inflicting the bite

  • Location of the bite

  • Type of injury inflicted

• Bites on the extremities are more likely to become infected than bites on the head, face, and neck

• Failure to elicit a history of provocation is important, because an unprovoked attack raises the possibility of rabies

• Human bites

  • Usually inflicted by children while playing or fighting

  • In adults, bites are associated with alcohol use and closed-fist injuries that occur during fights

• Infections following human bites are variable

  • Because bites inflicted by children are superficial, they rarely become infected

  • Bites by adults become infected in 15–30% of cases, with a particularly high rate of infection in closed-fist injuries

  • "Through and through" bites (eg, involving the mucosa and skin) have an infection rate similar to closed-fist injuries

• Cat bites

  • More likely to become infected than human bites

  • 30–50% of cat bites become infected

• Dog bites, for unclear reasons, become infected only 5% of the time

• Puncture wounds become infected more frequently than lacerations, probably because the latter are easier to irrigate and débride

• The bacteriology of dog and cat bites is polymicrobial

  • Over 50% of infections are caused by aerobes and anaerobes

  • 36% are caused by aerobes alone

  • Pure anaerobic infections are rare

• Pasteurella species are the single most common pathogen—75% of cat bites and 50% of dog bites

• Other common aerobes include

  • Streptococci

  • Staphylococci

  • Moraxella

  • Neisseria

• Common anaerobes include

  • Fusobacterium

  • Bacteroides

  • Porphyromonas

  • Prevotella

• Human bites are a mixture of aerobes and anaerobes in 54% and aerobes alone in 44%

• Staphylococci and streptococci are the most common aerobes

• Eikenella corrodens (isolated in 30% of infections), Prevotella, and Fusobacterium are the most common anaerobes

• Although the above-named organisms are the most common, numerous others have been isolated such as Capnocytophaga (dogs and cats), Pseudomonas, and Haemophilus, emphasizing the need to culture all infected wounds to define microbiology

• HIV transmission following a bite has been rarely reported; saliva not contaminated with blood is very low risk

Demographics

• About 1000 dog bite injuries require emergency department attention each day in the United States, most often in urban areas

• Dog bites occur most commonly in the summer months