Approximately 10%-15% of human bite wounds become infected owing to multiple factors. The bacterial inoculum of human bite wounds contains as many as 100 million organisms per milliliter and is made up of as many as 190 different species. Many of these are anaerobes that flourish in the low redox environment of tartar that lies between human teeth or in areas of gingivitis. Most injuries due to human bites involve the hands. Hand wounds, regardless of the etiology, have a higher rate of infection than do those in other a locations. (See Pathophysiology and Etiology.)
Infections associated with human bites are often far advanced by the time they receive appropriate care. Patients often wait until infection is well established before seeking medical treatment. These wounds are frequently more extensive than estimated on initial examination by the inexperienced observer and are frequently managed inadequately. (See Prognosis, Presentation, Treatment, and Medication.)
Evidence suggests transmission of human immunodeficiency virus (HIV) through human bites is possible but very unlikely. (See Pathophysiology, Presentation, and Workup.)
The goals of therapy are to minimize possible soft tissue deformity and to prevent or appropriately treat infection. Recognition of the high risk of infectious complications and early aggressive treatment are mandatory to prevent serious wound infection and its associated complications. [1, 2] (See Prognosis, Treatment, and Medication.)
Human bite wounds occur as 2 separate entities: clenched-fist injuries and occlusive bites.
Clenched-fist injuries are the most common and have the greater clinical significance. They occur as the closed fist strikes the teeth of another individual with sufficient force to create a small wound, usually 3-8 mm in length. The injury usually occurs over the dorsal surface of the third and fourth metacarpophalangeal (MCP) or proximal interphalangeal joints of the dominant hand. Because of the thinness of the skin in these areas, potential injuries include joint penetration, metacarpal fracture, and extensor tendon laceration. Injury to the digital nerve or artery is rare.
As the fingers extend following injury, the bacterial inoculum may be carried proximally with the extensor tendons. This makes adequate irrigation of the wound more difficult. These are the most serious human bite wounds, and they require the most aggressive treatment.
Occlusive bites occur when there is sufficient force to break the skin. Such injuries to the hand have a higher infection rate than similar bites to other parts of the body because of the thinness of the skin in this area.
When a finger is bitten, such as in a chomping-type injury, tendons and their overlying sheaths are in close proximity to the skin. The wound may appear to be a minor abrasion-type injury, but careful inspection is required to rule out deep injury.
Occlusive human bite wounds of the head and neck result in avulsion, laceration, and crushing of the tissues. Even so, when a tooth strikes the head, even a deep puncture wound may appear innocuous. However, deep, subgaleal, bacterial contamination is possible. This is especially true in young children who have relatively thin, soft scalp and forehead tissue.
Regardless of the mechanism and anatomic location of the bite wound, the composition of the bacterial inoculum is the same. Cultures of human bite wounds are commonly polymicrobial in nature, and aerobes and anaerobes are represented almost equally. Beta-lactamase production occurs frequently. Commonly isolated aerobes include Eikenella corrodens and Staphylococcus, Streptococcus, and Corynebacterium species. Staphylococcus aureus is isolated in up to 30% of infected human bite wounds and is associated with some of the most severe infections.
E corrodens is a slow-growing, facultative, anaerobic, gram-negative bacillus. It is frequently associated with chronic infection and abscess formation. This pathogen is isolated in 30% of human bite wounds. Other commonly isolated anaerobes include Bacteroides, Fusobacteria, Prevotella, and Peptostreptococcus species.