Antibiotic use in animals, and the impact on humans is a controversial area. At a conference a few years ago, one of the organizers posed the question, "What percentage of resistance in human pathogens is attributable to antibiotic use in animals?" They had people write their answers on cards, and later in the day they gave a synopsis of the results. Basically, the responses ranged from 0-96% (or something like that). That’s not surprising really, as there are a lot of opinions but there’s been a lack of good data. Clearly, use of certain antibiotics in animals in certain situations can lead to increased resistance in some human pathogens. Sorting out the "certains" and "somes" is the problem. It’s also clear that there’s massive overuse (and abuse) of antibiotics in human medicine that leads to lots of resistance.
The biggest problem is our current lack of data. It’s not for lack of trying, but it’s an extremely complex area. A study in the upcoming issue of Emerging Infectious Diseases (Collignon et al. 2013) starts to put some more solid numbers behind the concerns. The study took data from a variety of sources and attempted to figure out the number of human deaths from resistant E. coli (just one of the bugs we’re concerned about, but a big one) that is attributable to antibiotic use in animals. Their conclusion was that infections with E. coli resistant to 3rd generation cephalosporins (an antibiotic group which is used in some animals and is also important in humans), in which resistance was attributable to antibiotic use in poultry, accounted for 21 deaths and 908 hospital bed-days in the Netherlands in 2007. If this is extrapolated to Europe (which can only be done loosely because of differences in antibiotic use and infection trends between the vastly different EU countries), it would mean 1518 deaths and 67 236 hospital admissions. That’s a very small percentage of people in Europe overall, and a small percentage of all the people in Europe who die of resistant infections, but it’s still a lot and it’s therefor still a concern.
What does this mean more broadly for other countries, other bugs, other drugs? It’s hard to say. To quote the authors, "To more accurately estimate the associated increased deaths among persons resulting from third-generation cephalosporin use in poultry, detailed data from more countries is essential." I’d substitute "third-generation cephalosporin use" with "antibiotic use," since we also need to know about other drugs. It’s always amazed me how hard it is to get even a basic idea of how much antibiotic use occurs in people and animals, with profoundly different estimates by different groups (often driven by different agendas).
Antibiotic use is a necessity in some situations. We have a moral obligation to keep animals healthy, and healthy animals help make healthy food. However, at the same time, we need to think about standard practices and make sure antibiotics are truly being used wisely in both people and animals. Stopping all antibiotic use isn’t practical at this time, nor will it eliminate resistance. Knee-jerk reactions like simply banning antibiotics might actually make some things worse, if they result in other practices that also drive resistance (e.g. adding heavy metals like zinc to animal feed to help prevent diarrhea, resulting in the same pressure for antibiotic resistance, or replacing prophylactic treatment using drugs that are of limited concern in people with later use of therapeutic drugs that are important in humans). However, the use of antibiotics as a replacement for good management practices needs to end, and more thought needs to be given to how to use antibiotics wisely, effectively and sparingly – in all cases (animals and people).