There is an epidemic of antibiotic resistance and all contributors to that problem are important. There is consensus that the goal ought to be to reduce antibiotic use, in hospitals as well as in agriculture. Based on public data, the best estimate is that 70 percent of all antimicrobial use in the U.S. occurs as routine additives to animal feed for beef cattle, swine and poultry in the absence of clinical disease. About half are thought to be from medically important classes. The complexity of antibiotic resistance, the microbial ecosystem as well as the policy failure to collect much data on antibiotic use and the evolution of reservoirs of resistance all contribute to the situation where existing microbial risk assessments either greatly understate the problem or ignore important microbiological characteristics of the problem. These problems may be common to attempts to characterize public health risks in other issues of biological or geochemical systems, such as climate change or genetically engineered foodstocks.

Additional readings:
Tara C. Smith et al. Methicillin-Resistant Staphylococcus aureus (MRSA) Strain ST398 Is Present in Midwestern U.S. Swine and Swine Workers. PLoS ONE. 2009; 4(1).
Smith DL, Dushoff J, Morris JG. Agricultural antibiotics and human health. PLoS Med. 2005 Aug;2(8):e232. Epub 2005 Jul 5.
Kelly L, Smith DL, Snary EL, Johnson JA, Harris AD, Wooldridge M, Morris JG Jr. Animal growth promoters: to ban or not to ban? A risk assessment approach. Int J Antimicrob Agents. 2004 Sep;24(3):205-12.

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