Human Bite Infections 

Human bite wounds are notoriously deceptive and are often underestimated and undertreated. While controversies regarding optimal management continue, the basic tenets of meticulous wound care are no different than those for contaminated wounds.

The goals of therapy are to prevent or appropriately treat infection and to minimize the soft tissue deformity. Recognition and early, aggressive treatment are mandatory to prevent infection and associated complications.

Approximately 10-15% of human bite wounds become infected, and this considerable infection rate is multifactorial. Patients often wait until infection is established before presenting late in the course of their injury, thus necessitating medical attention. Wounds evaluated earlier are frequently more extensive than estimated on initial examination by the inexperienced observer and are frequently managed inadequately.

The bacterial inoculum of human bite wounds is rich in oral flora, as saliva contains as many as 100,000,000 organisms per mL, representing as many as 190 different species. Moreover, most of these injuries occur on the hands, and hand wounds of any cause have a higher infection rate than similar wounds in other anatomic locations.

The possibility of transmission of disease through human bites must be considered. Human bites have been shown to transmit hepatitis B, hepatitis C, herpes simplex virus (HSV), syphilis, tuberculosis, actinomycosis, and tetanus. Evidence suggests that it is biologically possible to transmit HIV through human bites, although this is quite unlikely.

For additional information on hepatitis B and hepatitis C, see Medscape’s Hepatitis B Resource Center and Hepatitis C Resource Center.

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 possess 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 middle finger metacarpophalangeal joint of the dominant hand. Potential injuries include joint penetration, metacarpal fracture, and extensor tendon laceration. Digital nerve or digital artery injury 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 the teeth bite a part of the body with sufficient force to violate the integrity of the skin. Although less serious than clenched-fist injuries, those occurring on the hand must be treated with greater attention, as they have a higher infection rate than occlusive bites to other parts of the body.

Regardless of mechanism and anatomic location, the bacterial inoculum deserves special consideration because it is composed of the rich oral flora of aerobes and anaerobes. Cultures of human bite wounds are commonly polymicrobial in nature, and aerobes and anaerobes are represented almost equally. Several bacterial species produce beta-lactamase, rendering them resistant to penicillin.

Commonly isolated aerobes include Eikenella corrodens and Staphylococcus, Streptococcus, and Corynebacterium species. Staphylococcus aureus is associated with some of the most severe infections, resulting in the highest complication rates. E corrodens is a slow-growing, gram-negative bacillus frequently associated with chronic infection and abscess formation. Commonly isolated anaerobes include Bacteroides and Peptostreptococcus species.

In addition to the infection risk, the potential for transmission of life-threatening disease is also present in human bites. Hepatitis B has been transmitted through human bites, as 75% of patients with hepatitis B infection have detectable antigen in their saliva. Less likely is the transmission of HIV, although several cases in the literature suggest this mode of transmission.^{[1, 2]} 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.

Frequency

United States

Human bites are believed to be the third-most-common bite wounds, following dog and cat bites. The true frequency is difficult to estimate because the vast majority probably go unreported and because many patients do not seek medical attention.

Of those reported, approximately 60% occur in the upper extremities, while another 15% occur in the head and neck region. The remainder occur on the breasts, genitals, thighs, and other areas.

Upper extremity bites most frequently occur on the dominant extremity. Head and neck injuries most commonly occur on the ears, nose, or lips.

Mortality/Morbidity

• The morbidity of human bites is related to infection and its sequelae.
• Prior to the era of antibiotics, up to 20% of hand bites required amputation of a finger.
• While amputation is necessary only in extreme cases today, bite wound infections are common and may result in permanent functional and/or cosmetic impairment.

Sex

• Clenched-fist injuries are predominantly a wound among males, a fact attributable to their more aggressive behavior.
• Occlusive bite wounds occur with equal frequency.

Age

• Clenched-fist injuries most commonly occur between adolescence and the fourth decade of life.
• Occlusive injuries are probably most common in toddlers placed in crowded daycare centers. These bites are usually superficial and rarely become infected.