ESSENTIALS OF DIAGNOSIS
Cat and human bites have higher rates of infection than dog bites.
Hand bites are particularly concerning for the possibility of closed-space infection.
Antibiotic prophylaxis indicated for noninfected bites of the hand and hospitalization required for infected hand bites.
All infected wounds need to be cultured to direct therapy.
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. Biting animals are usually known by their victims, and most biting incidents are provoked (ie, bites occur while playing with the animal or after surprising the animal while eating or waking it abruptly from sleep). Failure to elicit a history of provocation is important, because an unprovoked attack raises the possibility of rabies. Human bites are usually inflicted by children while playing or fighting; in adults, bites are associated with alcohol use and closed-fist injuries that occur during fights.
The animal inflicting the bite, the location of the bite, and the type of injury inflicted are all important determinants of whether they become infected. Cat bites are more likely to become infected than human bites—between 30% and 50% of all cat bites become infected. Infections following human bites are variable. Bites inflicted by children rarely become infected because they are superficial, and bites by adults become infected in 15–30% of cases, with a particularly high rate of infection in closed-fist injuries. Dog bites, for unclear reasons, become infected only 5% of the time. Bites of the head, face, and neck are less likely to become infected than bites on the extremities. “Through and through” bites (eg, involving the mucosa and the skin) have an infection rate similar to closed-fist injuries. Puncture wounds become infected more frequently than lacerations, probably because the latter are easier to irrigate and debride.
The bacteriology of bite infections is polymicrobial. Following dog and cat bites, over 50% of infections are caused by aerobes and anaerobes and 36% are due to aerobes alone. Pure anaerobic infections are rare. Pasteurella species are the single most common isolate (75% of infections caused by cat bites and 50% of infections caused by dog bites). Other common aerobic isolates include streptococci, staphylococci, Moraxella, and Neisseria; the most common anaerobes are Fusobacterium, Bacteroides, Porphyromonas, and Prevotella. The median number of isolates following human bites is four (three aerobes and one anaerobe). Like dog and cat bites, infections caused by most human bites are a mixture of aerobes and anaerobes (54%) or are due to aerobes alone (44%). Streptococci and S aureus are the most common aerobes. Eikenella corrodens (found in up to 30% of patients), Prevotella, and Fusobacterium are the most common anaerobes. Although the organisms noted are the most common, innumerable others have been isolated—including Capnocytophaga (dog and cat), Pseudomonas, and Haemophilus—emphasizing the point that ...