Small animal veterinarians may come under scrutiny for antimicrobial use

A recent New England Journal of Medicine editorial recommended banning the use of fluoroquinolones and third-generation cyclosporins in all animals, not just food animals, she reminded the audience. And new studies suggesting that resistant bacterial infections from pets may pose a threat to people have generated interest in the press.

"Our goal is to make sure we dot our i's and cross our t's and don't do anything wrong in terms of antibiotic usage so that when these articles come out, we cannot be blamed for (anything)," said Dr. Mealey, who is an assistant professor at Washington State University's College of Veterinary Medicine.

The attention that antimicrobial resistance has sparked in the scientific and popular press is well deserved. While the United States churns out 50 million pounds of antimicrobials each year, at least one form of microbial resistance has been described for every antimicrobial that's on the market.

People have blamed antimicrobial resistance problems on growing international travel, increased "pill popping" by people, and the use of the drugs in food animals. But while legislators have responded by limiting the use of antimicrobials in food animals, there has been little scrutiny of their use in small animal practice. This may soon change.

Several new studies have reported associations between resistant bacterial infections in people and exposure to dogs and cats. The Centers for Disease Control and Prevention recently reported three outbreaks—in Idaho, Washington, and Minnesota—in which pet owners, animal health workers, and contacts of these individuals became infected with multidrug-resistant Salmonella typhimurium. In each outbreak, isolates from dogs and cats were identical to those from humans, and all had a high degree of resistance.

Dr. Mealey noted that evidence did not prove whether humans gave the strains to animals, animals gave them to humans, or animals and humans both got them from the environment, but to some individuals, this didn't appear to matter.

In the discussion session of the CDC article, it was stated that the use of antimicrobial agents in veterinary facilities may have contributed to transmission of multidrug-resistant Salmonella.

"This is an article by the CDC, so people listen to it," she said. "The perception is that antibiotic use in that hospital is what contributed to the multidrug resistance in this particular Salmonella species."

The CDC study does not stand alone in implying that pets are a source of the problem, even though evidence is inconclusive. Two other reports attempt to link Escherichia coli urinary tract isolates from dogs and cats to people and imply that animal pathogens may contribute to human infections and stubborn strains.

Other scientific reports link resistant bacteria isolated from human patients to dogs and cats, including organisms such as methicillin-resistant Staphylococcus aureus and S intermedius as well as vancomycin-resistant enterococci.

Because of the increased scrutiny these reports may cause, small animal practitioners must make sure they understand the mechanisms of antimicrobial resistance and attempt to minimize them by using drugs appropriately and following infection control policies and procedures.

Human hospitals take two strategies in their attempts to minimize resistance. The first strategy involves restricting the use of antimicrobials by prohibiting the use of specific agents within the hospital, limiting prophylactic antimicrobial administration, rotating agents, and minimizing the use of pharmaceuticals with high resistance potential. Some argue that although this strategy is somewhat effective, resistance may simply shift to other drugs. The second strategy revolves around infection control procedures such as regular hand washing, screening and isolating high-risk patients, and barrier precautions. Although this, too, has been shown to be effective, opponents argue that this approach ignores the generation of resistant bacteria.

Neither strategy has been adequately assessed in veterinary hospitals, Dr. Mealey says, but it is likely that a combination of approaches will be necessary to lasso in and control the issue.

In addition to implementing infection control procedures, Dr. Mealey recommends that practitioners limit the use of antimicrobials to animals with documented infections, which may require more culturing of patient specimens; use agents with a narrow spectrum of activity, which may necessitate additional susceptibility testing; and ensure adequate drug concentrations at infection sites by adopting appropriate dosage intervals. Finally, clients must be educated about the importance of treatment duration.

If practitioners follow these courses of action, Dr. Mealey says, then the veterinary community will be able to respond if criticism is mounted against the use of antimicrobials in small animal practices.