Human bite infections
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.
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.
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 and symptoms
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.
The most common sign of infection from a human bite is inflammation, which usually develops within eight to 24 hours following the bite. The skin around the wound is red and feels warm, and the wound may ooze pus or a whitish discharge. Nearby lymph glands may be swollen, and there may be red streaks running up the arm or leg from the wound toward the center of the body. Complications can arise if the infection is not treated and spreads into deeper structures or into the bloodstream.
Live disease-causing bacteria within the bloodstream and tissues may cause complications far from the wound site, including transmission of HIV infection . Deep bites or bites near joints can damage joints and bones, causing inflammation of the bone and bone marrow, necrotizing fasciitis, or septic arthritis.
When to call the doctor
Parents should call the doctor or take the child to the emergency room for examination and treatment of any human bite severe enough to break the skin, no matter what part of the body is affected. Even wounds that appear to be minor abrasion-type injuries may prove to be deeper puncture wounds when the doctor examines them.
In most cases the diagnosis is made by an emergency room doctor on the basis of the patient's history.
The medical examination involves taking the history of the injury and assessing the type of wound and damage. The child's record of tetanus immunization and general health status are checked. An x ray may be ordered to assess bone damage and to check for foreign objects in the wound. In the case of a closed-fist injury, there may be fragments of teeth present in the wound. Wound cultures are done for infected bites if the victim is at high risk for complications or if the infection does not respond to treatment. If the child was bitten severely on the head, the emergency room doctor will call in a neurologist for consultation, particularly if the eyes, ears, or neck were injured or the skull was penetrated. Young children are particularly at risk for infection of puncture wounds from bites on the head because the skin on the scalp and forehead is relatively thin and soft. The doctor may also consult a plastic surgeon if the bites are extensive, if large pieces of tissue have been lost or if the functioning or appearance of the injured part of the body is likely to be affected.
Because the human mouth contains a variety of bacteria, the doctor may order a laboratory culture in order to choose the most effective antibiotic. Cultures are most commonly done when the wound has begun to show signs of infection.
Treatment depends on the wound type, its site, and such other risk factors for infection as the condition of the patient's immune system. All wounds from human bites are cleaned and disinfected as thoroughly as possible. The doctor will begin by injecting a local anesthetic in order to examine the wound thoroughly without causing additional pain to the child. The next step is to remove dead tissue, foreign matter, and blood clots, all of which can become sources of infection. This removal is called debridement. After debriding the wound, the doctor will cut away the edges of the tissue, as clean edges heal faster and are less likely to form scar tissue. The doctor will then irrigate, or flush, the wound with saline solution forced through a syringe.
Doctors do not usually suture a bite wound on the hand because the connective tissues and other structures in the hand form many small closed spaces that make it easy for infection to spread. Emergency room doctors often consult surgical specialists if a patient has a deep closed-fist injury or one that appears already infected.
Bites on the ear are also difficult to treat because the cartilage in the ear does not have a good blood supply. If the cartilage has been exposed by the bite, the doctor will administer intravenous antibiotics for 48 hours and delay closing the wound for 24 hours or longer following the injury.
The doctor will make sure that the patient is immunized against tetanus, which is routine procedure for any open wound. Because of risk of infection, all patients with human bite wounds should be given antibiotics. The usual choice for human bite wounds on the hand is a first-generation cephalosporin and either penicillin or amoxicillin-clavulanate (Augmentin). If the child has a weakened immune system, the doctor will prescribe either amoxicillin or erythromycin. Patients with severe closed-fist injuries may need inpatient treatment in addition to an intravenous antibiotic.
The prognosis depends on the location of the bite and whether it was caused by a child or an adult. Bites caused by children rarely become infected because they are usually shallow. Between 15 and 30 percent of bites caused by adults become infected, with a higher rate for closed-fist injuries.
The prognosis for restoring the function or appearance of a hand, ear, or other body part following a severe bite depends on the location of the bite, the promptness of treatment, and the availability of specialized surgical repair. Infections of the hand have a high rate of permanent scarring, tissue damage, and loss of function when treatment is delayed.
Prevention of human bite infections depends upon prompt treatment of any bite caused by a human being, particularly a closed-fist injury. Long-term prevention, particularly in young males, requires teaching children how to resolve arguments or quarrels without resorting to violence.
Biting is fairly normal behavior in toddlers and rarely reflects intentional malice. Children in this age group sometimes bite one another because they are over-stimulated or tired or because they have not yet learned to use words to express their feelings. Suggestions for preventing biting in young children include scheduling naps after highly stimulating activities, giving the child a washcloth or similar object to bite, and observing the child to see whether a particular person or situation is triggering the biting behavior. As has been mentioned earlier, toddlers' bites are rarely severe enough to cause a serious infection unless the bitten child has a weakened immune system.
Parental concerns for older children and adolescents include the possibility that the child is abusing drugs or alcohol, has a conduct disorder , or is being bullied, as well as fears of disfigurement or lasting injury from an infected bite on the face or hand.
See also Animal bite infections .
"Infections Caused by Bites." Section 5, Chapter 61 in The Merck Manual of Diagnosis and Therapy , edited by Mark H. Beers and Robert Berkow. Whitehouse Station, NJ: Merck Research Laboratories, 2002.
Stierman, K. L., et al. "Treatment and Outcome of Human Bites in the Head and Neck." Otolaryngology and Head and Neck Surgery 128 (June 2003): 795–801.
Talan, D. A., et al. "Clinical Presentation and Bacteriologic Analysis of Infected Human Bites in Patients Presenting to Emergency Departments." Clinical Infectious Diseases 37 (December 1, 2003): 1481–89.
American Academy of Emergency Medicine (AAEM). 555 East Wells Street, Suite 1100, Milwaukee, WI 53202. Web site: http://www.aaem.org.
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. Web site: http://www.cdc.gov.
Avulsion —The forcible separation of a piece from the entire structure.
Closed-fist injury —A hand wound caused when the skin of the fist is torn open by contact with teeth.
Debridement —The surgical removal of dead tissue and/or foreign bodies from a wound or cut.
Fasciitis —Inflammation of the fascia (plural, fasciae), which refers to bands or sheaths of connective tissue that cover, support, or connect the muscles and internal organs. Human bites can lead to infection of the fasciae in the hand.
Fight bite —Another name for closed-fist injury.
Irrigation —Cleansing a wound with large amounts of water and/or an antiseptic solution. Also refers to the technique of removing wax (cerumen) from the ear canal by flushing it with water.
Necrotizing —Causing the death of a specific area of tissue. Human bites frequently cause necrotizing infections.
Occlusional —Referring to a type of injury caused by the closing of the teeth on a finger or other body part. Occlusional injuries are also called chomping injuries.
McNamara, Robert M. "Bites, Human." eMedicine , August 23, 2004. Available online at http://www.emedicine.com/emerg/topic61.htm (accessed November 10, 2004).
Rebecca Frey, PhD