Antibiotic use in swine farms in Alberta

Dear Sir, The survey of antibiotic use in Alberta swine farms by Rajic et al (Can Vet J 2006;47:446–452) provides important new information on how these drugs are used by the swine industry. As the authors note, information about veterinary antibiotic use is necessary for fully evaluating the public health risks of this use, including the risk of selecting for antibiotic resistance. There is a broad scientific consensus in the medical and public health communities that routine use of antibiotics in livestock can foster the development of resistance that will negatively impact human health. The significance of resistance in livestock populations depends, in part, on how important the antibiotic drug is for human medicine. When they laud the low use of the “critically important” drugs, cephalosporins and fluoroquinolones on Alberta farms, the authors recognize these points. At the same time, however, the authors’ statement is misleading that use of important antimicrobials on Alberta swine farms is low, since the scientific and public health communities actually consider a much larger group of antimicrobials to be “critically important.” In early 2005 an international panel of experts, convened by the World Health Organization, created a list of “critically important drugs” for use in evaluating and managing the public health risk from veterinary drugs. The drugs most commonly added to feeds on the surveyed Alberta farms, the macrolide tylosin and penicillin used in combination with 2 other drugs, are included on the World Health Organizations list. Tylosin is not used in human medicine, but its use selects for resistance to erythromycin, another macrolide, which is the drug of choice for treating campylobacter, the most common bacterial enteric pathogen in Canada. The authors do in fact mention the public health concern raised by penicillin use on the Alberta swine farms, but they fail to acknowledge the concerns raised by the farms’ frequent use of macrolide antibiotics. While the authors should be commended for collecting and compiling antibiotic use information, by downplaying the importance to human medicine of the drugs used as feed additives, they paint a rosier picture than is warranted.