Is There Really a Connection between E. coli and Farming Methods?

Last Saturday, I linked to a WorldChanging post that said that E. coli O157 is linked to factory farming because it prefers to grow in grain-fed cows. I have just become aware that Tara Smith at Aetiology has written on this topic and the issue is not really clear-cut. There may indeed be a connection between grain-feeding and pathogenic E. coli, but the evidence is hardly unequivocal. Tara mentions a study that found

that when a long-term diet of hay was fed (greater than a month), the cattle still shed O157 (Appl Environ Microbiol. 2005 71:7974-9.) Another one found diet had no effect on O157 (J Anim Sci. 2006 84:2523-32). If anything's clear, it's that the link between diet and shedding of O157 *isn't* clear, despite what Plank claims.

Of course, knowing where our food comes from is important for many reasons and some links between factory farming and disease, like the evolution of antibiotic-resistance bacteria, are widely accepted. However, it is important that we base our decisions on the best science available and learn to tolerate some uncertainty.