Human bite wounds occur as 2 separate entities: clenched-fist injuries and occlusive bites.

Clenched-fist injury

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

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.

Disease transmission

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.

In addition to the acute risk of localized infection, human bites pose the potential for the transmission of systemic infections, which can be life threatening. Hepatitis B transmission via human bites is well documented. In approximately 75% of patients with hepatitis B, the antigen is detectable in their saliva, and it is approximately 100 times more infectious than HIV.

Less likely is the transmission of HIV, although several cases in the literature suggest this as a mode of transmission. [3, 4] HIV is found in the saliva of affected patients, although at lower levels than in the blood. In addition, salivary inhibitors render the virus noninfective in most cases. As a result, the risk of transmission of HIV via human bites is exceedingly low. [5]