Human Bites 

Human bite wounds are notoriously deceptive and are perhaps the most potentially disastrous type of bite wound because of the abundant pathogenic oral flora found in humans. The extent of injury is often underestimated and the wound is undertreated. Although controversies exist regarding optimal management of human bites, the basic tenets of meticulous wound care are the same as those with other contaminated wounds. 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.

Human bite wounds of the head and neck occur as occlusive bites with avulsion, laceration, and crushing of the tissues. Occlusive bites occur when a body part is bitten with sufficient force to violate integrity of the skin.

Bacterial inoculum of wounds by any mechanism or at any anatomic location deserves special consideration because it is composed of a rich mixture of aerobic and anaerobic oral flora. Human saliva can have as many as 100 million organisms per milliliter, and cultures of human bite wounds are commonly polymicrobial. Aerobes and anaerobes are represented almost equally in cultures.

Several bacterial species commonly found in human bite wounds produce the enzyme beta-lactamase, rendering them resistant to penicillin. Common aerobes isolated include Streptococcus species, Staphylococcus species, Eikenella corrodens, Haemophilus s pecies, and Corynebacterium. Staphylococcus aureus is isolated in up to 30% of infected human bite wounds and is associated with some of the most severe infections, resulting in the highest complication rates. E corrodens, a slow-growing gram-negative bacillus frequently associated with chronic infection and abscess formation, is isolated in 30% of human bite wounds as well. Common anaerobes isolated include Prevotella, Fusobacterium, Bacteroides, and Peptostreptococcus species. Morbidity of human bites is primarily related to infection and its sequelae, leading to permanent functional and/or cosmetic impairment.

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.

Although the transmission rate of HIV from saliva is epidemiologically insignificant, HIV can be found in the saliva of affected patients. However, salivary inhibitors with antiretroviral properties are thought to decrease the infectivity of HIV in saliva in most cases. As a result, the risk of transmission of HIV via human bites is exceedingly low; the real threats from a human bite are wound infection and hepatitis B and/or hepatitis C transmission.^[1]

Frequency

United States

Human bites are ranked as the third leading cause of all bites seen in hospital emergency departments (after dog and cat bites), accounting for 3.6-23% of bite wounds. However, the true frequency is difficult to estimate because most human bites are probably unreported or patients fail to seek medical attention. Of those reported, approximately 60% occur in the upper extremity, while 15% occur in the head and neck region, most commonly the ears, nose, or lips. The remainder occurs on the breasts, genitals, thighs, and other areas.

Mortality/Morbidity

Approximately 10-18% of human bite wounds develop infection. This substantial infection rate is multifactorial. The bacterial inoculum of a human bite is rich in oral flora, as saliva contains as many as 100 million organisms per milliliter, with as many as 190 different species.

Often, the severity of injury is initially underestimated, especially by the inexperienced observer, and appropriately aggressive treatment is not initiated. Patients frequently present days to weeks after injury, when infection is well established and medical attention is unavoidable. Moreover, most human bite injuries occur on the hands, and hand wounds of any cause have infection rates higher than similar wounds in other anatomic locations.

Various viral and other infectious diseases may be transmitted through human bites; examples include hepatitis B, hepatitis C, herpes simplex virus, syphilis, tuberculosis, actinomycosis, and tetanus. Evidence suggests that the transmission of HIV via human bites is biologically possible but unlikely.

Human bite wounds are generally thought to result in complications. However, compliant patients who promptly seek medical attention after injury have an excellent prognosis.

Sex

The incidence of human bites is more common among males.

Age

The peak incidence of human bites, including occlusive bites and clenched-fist injuries, is 10-34 years of age. Occlusive bites most commonly occur among toddlers in daycare centers; these bites are usually superficial and rarely become infected. Clenched-fist injuries occur when a closed fist impacts another individual's teeth, leaving an injury over the dorsal aspect of the metacarpophalangeal joints.