Bites including human and animal

OVERVIEW: What every practitioner needs to know

Are you sure your patient has a bite? What should you expect to find?

History

• What kind of animal caused the injury?

• How did the animal bite occur? For example, location, situation, the animal’s aggression, ownership of the animal.

• When did the injury occur?

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• A thorough past medical history including all medical conditions and medications.

• Allergies

• Tetanus immunization status

Physical exam

• Depth of injury

• Vascular supply of the site

• Evaluate joints close to the animal bite

• Nerve function

• Tendon function with extension and flexion

Signs of infection from the animal bite

• Fever, erythema, swelling, tenderness, purulent drainage, foul odor, and lymphangitis are key findings that suggest a wound is infected.

• Inflamed, warm, tender joints when a bite is close to a joint are concerning for septic arthritis.

• Clenched fist injury (sustained during fist fights) presents with small wounds around the metacarpophalangeal (MCP) joints and will have erythema, purulent drainage and tenderness.

• On physical exam for clenched fist injury or any animal bite that is close to a MCP joint, the wound should be examined on both extension and flexion of the joint to ensure the tendon sheath has not been compromised.

• Pasteurella multocida infection can occur after dog or cat bites. These infections develop rapidly and can start showing signs of infection such as erythema, edema and tenderness 12-24 hours after a bite.

• Signs of infection from a cat bite usually occur 12 hours after the bite.

• Signs of infection from dog bites usually occur 24 hours after the bite.

• Capnocytophaga canimorsus can cause a systemic illness after a dog bite. Systemic signs such as fevers, petechial rash, maculopapular rash, cellulitis, hypotension, and sepsis will be seen in these patients.

• Cat scratch disease is a syndrome characterized by regional lymphadenopathy that is painful. There can also be low-grade fever, malaise, fatigue, headache, nausea, and anorexia.

• Rat-bite fever can occur after a bite from rats, mice, squirrels, or gerbils. It can also occur through exposure to rat feces or urine. Symptoms start 3-7 days after exposure and include rigors, fever, petechial or purpuric rash.

• Rabies should always be a consideration with animal bites. In the US most rabies cases are transmitted from bats or non-domesticated animals instead of domestic animals. Prodrome symptoms include fever, malaise, anorexia, vomiting, paresthesia, pruritis, or pain. Encephalopathic symptoms such as hallucinations, bizarre behavior, agitation, and hydrophobia can also occur. Paralysis followed by coma and death are likely.

How did the patient develop disease from the bite? What was the primary source from which the infection spread?

• The source of the infection usually comes from the oral flora of the animal’s mouth. It can also be from the feces of the animal, soil, or the natural flora of the skin of the victim.

• Cat bites are usually puncture wounds. The long, slender teeth can cause deeper wounds which are at more of a risk for osteomyelitis and septic arthritis.

• Dog and cat scratches can introduce infection as well.

• Dog bites most often are on extremities. For children younger than 4 years old, the injuries are more likely to be on the neck and face.

• Human bites are frequently related to aggression. Clenched fist injury are the most prevalent human bites. They can be severe due to the close proximity of teeth to the MCP joints. With extension of the hand, bacteria can be inoculated into the joints.

Which individuals are of greater risk of bites?

Risk factors for animal bites

• Pets are the most common offending animal. Most patients who are bitten are familiar with the animal that bit them.

• Human bites become infected more frequently.

• Most mammalian bites are caused by dogs.

• Dog bites occur most frequently in the age group of 2-19.

• German shepherds, pit bull terriers and rottweilers account for the majority of dog bites.

• Dog bites occur more often in males.

• Cat bites occur more often in females.

Risk Factors for infection

• Location on hand, foot, major joint, scalp, or face

• Puncture wounds

• Crush injuries

• Treatment delay greater than 12 hours

• Age greater than 50 years old

• Immunosuppressive agents

• Corticosteroids

• Splenectomy

• Alcohol abuse

• Diabetes Mellitus

• Systemic Lupus Erythematosus

• Vascular disease

• Pre-existing edema of affected extremity

What laboratory studies should you order and what should you expect to find?

Results consistent with the diagnosis

• Complete blood count

• Gram stain from wound

• Culture from wound

• Blood cultures, aerobic and anaerobic

• ESR and CRP to assess for osteomyelitis or septic arthritis

• Peripheral blood smears should be used to look for eschariform lesions when concerned about Capnocytophaga canimorsus infection.

Results that confirm the diagnosis

• Cultures may not come back positive even when wound is infected

• Leukocytosis suggests infection

• Elevated C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can be seen with osteomyelitis

What imaging studies will be helpful in making or excluding the diagnosis of bites?

• Radiographs can help identify osteomyelitis or fracture.

• Ultrasound can also be used to evaluate for abscess.

• Computed tomography (CT) scan can be used for evaluation of head and neck wounds.

What consult service or services would be helpful for making the diagnosis and assisting with treatment?

If you decide the patient has a bite, what therapies should you initiate immediately?

Surgical consult should be considered when a wound is deep and has potentially penetrated bones, tendons or joints. A surgical consult should also be considered in patients with facial wounds and possible vascular or nerve injury.

Key principles of therapy:

• Establishment of last tetanus vaccination is imperative. If the patient has had a tetanus shot in the past ten years, then a tetanus toxiod booster should be given. Tetanus immune globulin should be given if the patient has not received a tetanus vaccination in the past ten years or it cannot be confirmed.

• Empiric antibiotic therapy should be started on all wounds inflicted from an animal bite unless they have presented after 72 hours and have no sign of infection.

• Rabies vaccine should be given in patients who have been bitten by an animal that is high risk for rabies. If it is deemed high risk then the patient should be given rabies immune globulin and the rabies vaccine. If the patient has already been immunized for rabies then the patient will not need the rabies immune globulin. It is important to start these things as early as possible.

• Patients who have been bitten by a human need to be evaluated for hepatitis B. If the patient has not been vaccinated or is negative for anti-hepatitis B antibodies and is bitten by someone who is hepatitis B positive, should be given hepatitis B immune globulin and the hepatitis B vaccine. If this information is unavailable then the hepatitis B vaccine series should be started.

• HIV post-exposure prophylaxis should be discussed with all patients who have been exposed to a human bite. The risk of infection with HIV is small after a bite but is possible.

1. Anti-infective agents

If I am not sure what pathogen is causing the infection what anti-infective should I order?

Empiric Therapy:

• For dog and cat bites, Staphylococcus aureus, Pasteurella species, Capnocytophaga canimorsus, Streptococci and oral anaerobes should be covered.

• For human bites, Staphylococcus aureus, H. influenzae, and beta-lactamase positive anaerobes should be covered.

• Extended spectrum beta-lactamase antibiotics should be used for coverage of animal and human bites.

• Penicillin allergic patients can be given clindamycin with trimethoprim/sulfamethoxazole or a fluoroquinolone.

Table I presents common bacteria from bite wounds.