Bite Wound Infection

Introduction:

Bite wounds are often found on the head and neck in young children, while in older children and adolescents, they are common on the limbs. These injuries can range from minor requiring no medical intervention to severe cases causing significant soft-tissue damage. Bites can introduce unusual pathogens from saliva, with infection risk ranging from 10 to 20 percent and 30 to 60 percent of infections being mixed aerobic-anerobic. Prophylactic antibiotics are recommended for high-risk wounds based on factors like type, location, biting animal species, and patient characteristics.

Animal bites are prevalent, with 60 to 80 percent from dogs and 20 to 30 percent from cats; bites from other animals (rabbits, guinea pigs, mice, rats, hamsters) are less common. Children are often victims. Human bites constitute up to 20 percent of urban bite injuries, featuring a broad spectrum of injuries, and infectious complications, often involving unusual pathogens, are frequent.

What Are the Symptoms of Bite Wound Infections?

Common Symptoms:

• Redness, swelling, and warmth around the wound.
• Pain or tenderness.
• Pus drainage from the wound.
• Fever.
• Chills.
• Fatigue.
• Swollen lymph nodes around the wound.

Other Symptoms May Include:

Animal bites exert local force, causing a range of injuries from superficial abrasions to severe degloving injuries with potential tissue loss, even affecting underlying bone. Skull perforations and avulsion injuries have been documented.

Cat bites typically result in punctate injuries with deep feline saliva inoculation. It is crucial to recognize that deep tissue layers can slide during a bite, leading to potential underestimation of injury depth, especially on hands where the periosteum and joints may be penetrated.

Fist-against-teeth wounds often involve metacarpophalangeal joint capsules and proximal phalanges. Bite wounds can be classified based on the involvement of deeper structures and the presence of vascular or peripheral nerve injury as follows:

• Grade I: Superficial skin lesion, torn skin, scratched skin, bite canal, crushing injury.
• Grade II: Wound extending from the skin to the fascia, muscle, or cartilage.
• Grade III: Wound with tissue necrosis or tissue loss.

Based on severity, bite wound can be categorized as:

• I: Superficial injury not involving muscle.
• II: Deep injury involving muscle.
• III: Deep injury involving muscle, with loss of tissue.
• IVA: The above (I, II, III), and injury to vessels or nerves.
• IVB: The above (I, II, III, IV), and bone involvement.

What Does an Animal and Human Bite Look Like?

Aggressive breeds like pit bulls, American Staffordshire terriers, bull terriers, rottweilers, and German shepherds are prominent in lethal cases. Fatal attacks often go unnoticed and typically involve vulnerable victims, especially elderly individuals and small children. Multiple dog attacks can result in extensive injuries. Children under four commonly suffer severe head and neck injuries, given their small and malleable skulls. Fatal outcomes usually result from vascular injuries leading to exsanguination, traumatic brain injury, decapitation, or air embolism.

Human bite wounds, seen as oval or semilunar hematomas and abrasions, can result from sexual crimes, child abuse, physical altercations, self-defense bites, or consensual sexual activity. Indirect bites, caused by a fist hitting another person’s teeth, have a specific pattern known as reverse bite injury, clenched fist injury, or fight bite. Direct occlusion bites may show a distinct impression of the biter’s teeth, with forensic assessment relying on detailed photographic documentation and DNA testing of fresh wounds. Specialized self-drying DNA swabs are used to collect saliva from the skin region in contact with the assailant, aiding in identification in forensic investigations.

What Are Rabies?

Rabies is a viral infection caused by an animal bite or a scratch, which is serious and life-threatening. It is transmitted through saliva in the infected animal when in contact with the open wound or mucus membranes. It attacks the central nervous system with symptoms including fever, headache, and muscle spasms. As the disease progresses, it causes hallucinations, delirium, and paralysis. Once the symptoms begin to appear, it becomes fatal.

Animals such as dogs, cats, bats, foxes, raccoons, etc., can cause rabies. The rabies vaccine prevents rabies infection in people bitten by an infected animal. It is the most influential vaccine to prevent the disease if given immediately after the bite or a scratch occurs. The first injection is given after the bite or scratch, followed by injections three, seven, and 14 days after the first injection. Any animal can transmit this virus, and it is essential to seek medical care to prevent the infection and the treatment required.

What Are the Microorganisms Involved in Bite Wound Infection?

The microorganism that can cause infection followed by a bite wound may involve various species, such as:

• Dog Bite: Leptospira, Rabies virus, Clostridium tetani, Francisella tularensis.
• Cat Bite: Bartonella henselae, Francisella tularensis.
• Rodent: Leptospira.
• Rat: Spirillum minus, Streptobacillus moniliformis.
• Monkey: Herpes simiae (B virus).
• Other Animals: Brucella.
• Man: Hepatitis B and C virus, HIV (human immunodeficiency virus), Treponema pallidum.

What Is the Risk of Infection in Bite Wounds?

Reported infection rates for bite wounds vary, with approximately 10 to 20 percent overall infection rates, including 30 to 50 percent for cat bites, 5 to 25 percent for dog bites, and 20 to 25 percent for human bites. Infection risk is influenced by factors such as wound nature, location, patient characteristics, and the biting animal species. High infection rates are observed in deep, contaminated wounds, those causing marked tissue destruction, edema, and poor perfusion, especially on the hands, feet, face, and genitals, as well as wounds involving bones, joints, or tendons.

Neonates and infants face a higher infection risk than older children and adults. Patients with immune dysfunction (like hepatopathy, AIDS, cancer, neutropenia, asplenism, diabetes, immunosuppressant, or corticosteroid use) are at higher risk. However, individuals without predisposing factors can experience severe or lethal infections from bite wounds.

How Are Bite Wound Infections Diagnosed?

The diagnosis of bite wound infections includes:

• A detailed history of the patient, including vaccination status, time, location or site, bite circumstances, and provoking factors, is needed in case of animal bite species and owner, vaccination status (rabies), and state of health of the animal.
• Risk factor assessment involves the evaluation of factors contributing to complications such as sepsis.
• Physical examination includes evaluation of symptoms such as fever, nature, site, and extension of the wound, examination of foreign bodies, secretion, inflammation, lymphadenopathy, and vascular injuries.
• Wound inspection includes evaluation of the bite wound to determine the involvement of muscle, joint, vascular, and nervous tissue and also signs of infection.
• Laboratory tests such as complete blood count (CBC), tissue swab or secretion sample for bacteriological culture (infection and colonization), CT or MRI in case of head injury, and ultrasonography for suspected abscess formation and to evaluate soft-tissue fluid collection.

What Are the Treatment Options for Bite Wound Infection?

Treatment for bite wound infection includes:

General Measures:

• Cleansing (one percent iodine solution), irrigation using normal saline or antiseptic solutions, and debridement of the devitalized tissue.
• Limb immobilization, inpatient treatment, or outpatient follow–up.
• Infection prophylaxis includes indications of immunization like tetanus or rabies, as well as antibiotics for high-risk wounds.

Debridement: Removing torn, crushed, and devitalized tissue, necrosectomy is superior to irrigation but is limited to anatomical constraints. Surgical debridement for the head and neck is less extensive than for the limbs. Clenched fist injuries necessitate comprehensive treatment, including debridement, tenosynovectomy, and daily hand baths. Joint involvement without cartilage damage may be managed with antiseptic irrigation and drainage.

Wound Irrigation: Deep irrigation through an infusion catheter or cannula is employed to eliminate foreign bodies and pathogens. Pressure-based irrigation is not employed due to the risk of uncontrolled bacterial spread into deeper tissue layers. Normal saline is commonly used for irrigation.

Wound Closure: Face wounds are closed primarily, and successful replantation and plastic surgical reconstruction with ear cartilage grafts are feasible. Dog bite wounds can be sutured through they are old. Primary closure is not recommended for puncture wounds with deep pathogen inoculation, hand bites, and human bites.

Antibiotic Treatment:

• Surgical debridement surpasses irrigation alone in effectiveness.
• Prophylactic antibiotics are warranted only in high-risk scenarios.
• Infections are addressed with targeted antibiotic therapy.
• Antibiotics such as Aminopenicillin and the beta-lactamase inhibitor, Piperacillin, Carbapenam, Cefotaxime and Metronidazole, and Ciprofloxacin (in case of Penicillin allergy) are used.

Prevention:

• Animal bites are preventable injuries, requiring a collective effort.
• Effective prevention involves implementing appropriate rules for animal care, fostering social competence among animal owners, and educating children on proper behavior around animals.
• Immunization or vaccination against rabies and tetanus can help in preventing bite wound infection.

Conclusion:

Bite wound infections are caused by human or animal bites. The infection depends on the type and severity of the bite. Proper treatment is taken to prevent complications associated with bite wound infections, including antibiotics and dressing cleaning of the wound. The rabies vaccine is taken to prevent rabies infection.