A study conducted by Ohio State University food-animal health researcher Jeff LeJeune found similar numbers of food-borne pathogens and antimicrobial-resistant bacteria in samples of ground beef from conventionally reared cattle and from those whose labels claimed to have come from cows that didn’t receive any antimicrobial agents.

LeJeune said the percentage of contamination and concentration of coliforms found in this study are similar to those reported in the Nationwide Federal Plant Raw Ground Beef Microbiological Survey of 1994. By contrast, E. coli contamination in this study was detected in only half as many samples as reported 10 years ago, and E. coli concentration among positive samples was lower than in the federal survey.
"This data suggest that the magnitude and frequency of contamination of ground beef with E. coli has decreased over the past decade, possibly due to the proactive efforts of the processing industry to control microbial hazards," he pointed out.