Beware of dog, but don’t ignore dangers of cat, human bite wounds

Accurate assessment, care prevent wound infections

Bite wounds may be initially evaluated in the emergency department, but most wound specialists who have treated bites never forget the experience.

Samantha Morgan, RN, CRRN, CCM, ET, director of rehab services for Laurel Health Care Corp. in Westerville, OH, reports that the bites she has treated remain vivid in her memory. "Bite wounds are complicated by a number of factors," she says, noting that bite wounds carry a high risk of deep-tissue inoculation with bacteria, depending on the severity of the bite. Adults who’ve been bitten often present in the ED impaired by alcohol, which makes history taking, evaluation, and treatment difficult. Children who are bitten frequently are terrified, making assessment and treatment a challenge.

"With bite wounds," Morgan says, "the wound specialist may be asked to step in and assist in identifying and addressing the plan of care for the individual based on the degree of injury, the cognitive level of the patient, the management of the wound site, and the case management of the patient if significant tissue has been avulsed or there is likelihood of complications such as infection.

"As a wound ostomy and continence nurse, I am also quite interested in knowing what the emergency staff’s protocols are. While I may not be involved initially, I may well be part of the follow-up," Morgan says. There’s also a potential bite wound risk for home care nurses and affiliated health care professionals who deliver care in the homes of patients with pets.

Preventing bite wounds from becoming slow-healing or chronic requires quick, accurate intervention. Patients at highest risk of bite wound complications are those over 50, diabetics, asplenics, alcoholics, or those who have a lowered immune response due to chemotherapy, AIDS, corticosteroid therapy, prosthetic or diseased cardiac valve, or prosthetic or diseased joint.1

Alexander Trott, MD, professor of emergency medicine at the University of Cincinnati College of Medicine, says appropriate bite wound management depends on the type, location, and size of the bite. "My outpatient recommendation is that all bites from any source should be given a thorough cleaning immediately with soap and water, preferably using an antibacterial soap," Trott says. He adds that a dog bite where the skin is bruised but not broken must be watched carefully for signs of infection. Redness, heat, purulence, tenderness, extreme swelling, or lymphangitis mean the patient needs immediate medical treatment.

If the skin is broken or torn, the patient should see a doctor, no matter what animal delivered the bite. For larger wounds that break both the epidermis and dermis, Trott has developed standard wound management procedures. (See Trott’s bite wound management procedures, p. 39.) Wound caregivers also must be sure the wound is sufficiently incised to permit effective irrigation and debridement.1

Antibiotic prevention of bite wound infection remains controversial. Early studies reported rates of infection as high as 45% after dog or cat bites; in subsequent studies, the incidence dropped to under 5%.3 (When antibiotics are called for, Trott recommends reviewing the table above to determine which one to use.) "It’s particularly helpful if you have a patient who’s allergic to common antibiotics," he says, "because the table makes it easy to choose an alternate."

Trott emphasizes that for any cat or human bite, even if it doesn’t break the skin, the patient requires immediate medical treatment because these bites can become badly infected. "Human mouths are sewers. If we have a human bite to the hand, including bites to a clenched fist, we always admit the patient for intravenous antibiotics because we know how terrible the infection can be." Human bites arouse special concern because they can transmit organisms such as hepatitis B virus and syphilis.2 "In spite of all the bacteria you hear about in dogs’ mouths, they’re actually cleaner than humans or cats," Trott adds.

Though 30 different genera of microorganisms have been cultured from a dog’s mouth,1 the number of bacterial species implicated in actual infections is much smaller. A recently published study3 of 50 patients with dog bites and 57 patients with cat bites found a median of five bacterial isolates per culture, with 50% of dog bites and 75% of cat bites containing Pasteurella species. Cultures obtained at the time of injury are of little value because they cannot be used to predict whether infection will develop, or if it does, what the causative pathogens are.2

Thin fangs can push germs deep into wounds

Cat bites and scratches that break the skin have a fairly high chance of becoming infected. "There’s a bacteria in the cat’s mouth called Pasteurella multocida. If it sets up in the skin and starts multiplying, within 24 hours that patient will have one of the nastiest-looking wound infections he or she, or maybe even the doctor, will ever have seen," Trott says. "Part of the reason is that cats have very thin fangs, and those fangs can be driven deep into the wound. Sometimes it doesn’t look as bad because it’s a very small little wound. But in fact that fang might have been in very deep and pushed this germ down into the skin." Rodent bites are considered relatively low-risk. Tissue-crushing bites from herbivores such as horses and cows and bites from carnivores over joints are considered high-risk.

Most animal bite wounds in this country are inflicted by domestic animals, sometimes by the very canines and felines we consider to be our friends. Though estimates of the number of wounds from bites vary considerably, the lowest is in the millions of incidents, with the highest number being dog bites to children. The majority of bite wounds are to the extremities; however, in children, especially those under age 9, the face and head are most often bitten. Bite injuries are most likely to occur in children, with a peak incidence between the ages of 5 and 14.

Leslie Sinclair, DVM, director of veterinary issues for companion animals for the Humane Society of the United States (HSUS) in Washington, DC, says the biggest problem in assessing numbers of animal bite incidents is that there’s no national reporting database. She adds that HSUS uses the estimate of 4.7 million dog bites annually in the United States derived from a 1996 study performed by the Centers for Disease Control and Prevention in Atlanta. "400,000 is probably not a bad estimate of cat bites," Sinclair says.

Whatever their incidence, appropriate care for bite wounds may include sutures. "There is a good deal of controversy about suturing bite wounds," Trott says. "If it’s a large, disfiguring wound, then suturing has to be considered, especially in children. That should be the decision of a physician and possibly also of a consulting physician, like a plastic surgeon. It’s a complicated decision based on the anatomic location and the type of bite and the potential for disfigurement."

The suturing issue is complex, agrees Laura Pimentel, MD, FAAEM, who chairs the department of emergency medicine at Mercy Medical Center in Baltimore. "It depends on the age and location of the wound as to whether we would put any stitches in it or not. We tend to shy away from that, but if it’s in a place that appears to be well-vascularized, like the face, we’ll go ahead and suture. On a hand, we would never do that."

Pimentel says it’s critical in emergency room care to explore the wound very carefully to determine if there’s any damage to neurovascular structures, tendons, or penetration into a joint space. "Depending upon the location and depth of the wound, we will sometimes X-ray to make sure there’s not a tooth left in there," she says. "Probably any wound to the hand we would X-ray." She emphasizes that the most important treatment factor is the local wound care, which includes appropriate irrigation and debridement of the bite site and a tetanus shot for any patient who hasn’t had one in the previous five years.

Pimentel does not admit bite wound victims to the hospital unless there already is a serious infection, or the patient is diabetic or needs surgery. "The underlying health status of the patient is very important," she adds. "We worry more about a patient who is diabetic or immunocompromised for any reason." The antibiotic Pimentel uses most commonly is Augmentin, a combination of amoxicillin and clavulanate. She says Augmentin has very good broad-spectrum coverage for most of the bacteria of concern in a bite wound.

Possible rabies exposure is another major risk incurred with bite wounds. Though most rabies risk in this country today does not come from pets, anyone bitten by a stray dog that can’t be captured and held for observation should notify public health authorities. Tourism can significantly increase rabies exposure and risk. Trott observes that tourists can easily be exposed to rabid dogs along the Mexican border, and adds that "90% of stray dogs in Mexico carry rabies."

When rabies exposure occurs, two types of treatment come into play. The first is with rabies immune globulin, which involves actually injecting the antibodies to rabies into the patient. The second is vaccination. According to Pimentel, a patient who’s been bitten by a wild animal would get both. "Half the dose of immune globulin goes right into the area of the bite, the other half in the arm. Patients also get the first dose of the five-shot series of the vaccine."

Though some breed afficionados may tell you otherwise, the Humane Society of the United States’ statistics show that certain breeds of dogs are responsible for more than their proportionate share of bite wounds. "Some of the dog species are bred for violence," Pimentel notes. "I know there have been more than a few deaths, particularly in children who’ve been mauled by these animals."

As Morgan points out, "Wound management is a 24-hour-per-day job, especially in my neighborhood. It’s important for me to be able to advise the bitten or the parents of the bitten in the appropriate management of this type of injury. I welcome any new info the physicians and veterinarians can offer so that I can be a better resource for the health care consumers around me."

References

    1. Trott A. Wounds and Lacerations: Emergency Care and Closure. 2nd ed. St. Louis: Mosby; 1997.

    2. Fleisher G. The management of bite wounds. N Engl J Med 1999; 340:138-140.

    3. Talan D, et al. Bacteriologic analysis of infected dog and cat bites. N Engl J Med 1999; 340:85-91.