Cat, Dog and Other Bites

DOCTOR'S VIEW ARCHIVE

Cat and dog bites carry many serious infections (some of which are not looked for in routine laboratory tests). That is according to a report on January 14, 1999 in The New England Journal of Medicine by David Talan of the University of California, Los Angeles (UCLA) and the Emergency Medicine Animal Bite Infection Study Group.

In a prospective (forward-looking) study involving 18 emergency departments, patients were enrolled who met stringent criteria for infection from a bite wound.

Specimens from their wounds were tested for bacteria at a research microbiology laboratory and, in some cases, at local hospital laboratories. The culture tests were designed to detect both aerobic bacteria (that grow in the presence of oxygen) and anaerobic bacteria (that require an atmosphere low or lacking in oxygen).

Dr. Talan and his coworkers "exquisitely documented the microbiologic makeup" of cat and dog bites. The most common infectious agents they detected belonged to the Pasteurella family of bacteria which are associated with infections having a rapid onset. Other bacteria encountered included staphylococci (staph) and streptococci (strep). Staph aureus was present in 20% of dog bites and 4% of cat bites, and Strep pyogenes was present in 12% and 0% of dog and cat bites, respectively. A host of other bacterial causes of disease, including some never before detected in cat or dog bite wounds, rounded out the list.

"Animals can inflict serious, even fatal, injuries by biting. Each year attacks by dogs cause 10 to 20 deaths in the United States, predominantly among children," noted Dr. Gary R. Fleisher in an editorial accompanying the report in The New England Journal.

"Even apparently minor wounds require careful exploration," stated Dr. Fleisher, "because injuries that appear to be superficial may overlie fractures; involve lacerated tendons, vessels, or nerves; extend into body cavities; penetrate joint spaces; or damage structures such as the eye."

As a rule, cat and dog bite wounds should be treated and left open initially. This is true if they are punctures, if the bites are not potentially disfiguring, if they only involve the arms or legs (including the hands or feet) or if the bites to such areas occurred more than 6-12 hours earlier (because the bacteria would be closed into the wound).

An exception to the open-wound treatment involves cuts to the face from cat or dog bites. Facial wounds are almost always closed to avoid disfigurement.

About 85% of cat and dog bites harbor bacteria that can potentially cause disease. To lower the concentration of bacteria in contaminated wounds (and decrease the chance of infection), copious irrigation with water or sterile saline (salt) solution at high pressure is very helpful. Removal of dead tissue (a process called debridement) may be done by the doctor to further decrease the likelihood of infection.

The use of antibiotics to prevent infection after bites is controversial. Antibiotics are usually not given routinely. They are almost always recommended for "high-risk" wounds such as those with "deep punctures (particularly if inflicted by cats), those that require surgical repair, and those involving the hands."

If an antibiotic is to be prescribed, Dr. Fleisher recommends in most cases it be (in technical terms) "a (beta)-lactam antibiotic such as amoxicillin combined with a (beta)-lactamase inhibitor." (These are antibiotics that are specialized to treat bacteria that have developed certain powers of resistance to traditional antibiotics.)

If a wound becomes overtly infected, some or all of any sutures that have been put in are removed, pus is drained and usually antibiotics are given by vein. Severe infections can develop after bites. (Fever after a bite in someone who is immune suppressed is a danger signal.)

All patients with a bite should receive a tetanus shot, given the risk of tetanus after all kinds of bites, not just those of dogs and cats.

Rabies transmission should always be suspected as well, especially from the bites of certain types of animals such as bats. Dr. Fleischer advises that "all domestic animals -- as well as all wild animals, if they can be caught -- that behave wildly or erratically after biting a person should be killed so that their brains can be evaluated for rabies."

No essay on bites is complete without important consideration of human bites (when one person bites another) for comparison and illustration. (When the boxer Mike Tyson bit his opponent, Evander Holyfield, he put him at risk for more than a disfigured ear). With a bite, people can transmit organisms such as the human immunodeficiency virus (HIV), the hepatitis B virus, and even syphilis!

SOURCES:

1. DA Talan, DM Citron, FM Abrahamian, GJ Moran, EJC Goldstein, for the Emergency Medicine Animal Bite Infection Study Group. Bacteriologic Analysis of Infected Dog and Cat Bites. New Engl J Med 1999;340:85-92.
2. GR Fleisher. The Management of Bite Wounds. New Engl J Med 1999;340:138-140.

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