Human Bite Infections Health Article

Definition

Human bite infections are potentially serious injuries that develop when a person's teeth break the skin of the hand or other body part and introduce saliva containing disease organisms below the skin surface.

Description

There are three common types of injuries caused by human bites:

• Closed-fist injuries: These are injuries to the hand sustained in a fight when the skin over the knuckles is broken and penetrated by the teeth in the opponent's mouth.
• Occlusional or chomping injuries: This type of injury results when a person bites down hard on another person's ear, nose, or finger.
• Avulsion injuries: Avulsion is the medical term for a ripping or tearing of the skin or body part. Human bites on the head and neck may cause avulsion injuries to the ears, nose, cheeks, or scalp.

Demographics

Exact statistics on human bite wounds are difficult to establish, although one figure for closed-fist bites in the United States is 11.8 per 100,000 persons per year. Bite injuries account for about 1 percent of emergency room admissions in the United States and Canada, with human bites ranked third after dog and cat bites respectively. About 70 percent of all human bite wounds reported in North America involve adolescent males or adult males below the age of 40.

Closed-fist and chomping injuries account for most human bite infections. In one study done in a California hospital, closed-fist injuries accounted for 56 percent of the human bite infections treated, with the remaining 44 percent caused by occlusional bites.

Causes

In children, bite infections result either from accidents during play or from fighting. Toddlers often bite one another when they are roughhousing; however, they usually do not bite hard enough to cause serious injury. Deep bite wounds on a young child may indicate abuse by an adolescent or adult.

Most infected human bites in adolescents and adults result from fighting, and some are inflicted on police officers or institutional staff. Alcohol or drug intoxication is an additional factor in closed-fist injuries.

The structure of the human hand contributes to the frequency with which closed-fist bites are likely to become infected. When a person closes the hand to make a fist, a tendon known as the extensor tendon is stretched. When the person hits the teeth in another person's mouth hard enough to break the skin, bacteria from the saliva in the mouth get into the tendon and its overlying sheath. After the hand is opened, the extensor tendon relaxes and returns to its normal position underneath the skin, but it is now carrying bacteria with it. The bacteria can then invade tissues that are very difficult to cleanse when the person finally seeks medical help. A similar chain of events is involved in infections of chomping injuries. Like the back of the hand, the fingers also have tendons lying just below the skin. A chomping bite that is hard enough to break the skin can also introduce bacteria into the finger tendons or their sheaths.

The infection itself can be caused by a number of bacteria that live in the human mouth. These include streptococci, staphylococci, anaerobic organisms, Prevotella melaninogenica, Fusobacterium nucleatum, Candida spp. and Eikenella corrodens. Infections that begin less than 24 hours after the injury are usually produced by a mixture of organisms and can produce a necrotizing infection (causing the death of a specific area of tissue), in which tissue is rapidly destroyed.