Eighty percent of the antibiotics sold in the United States goes to chicken, pigs, cows and other animals that people eat, yet producers of meat and poultry are not required to report how they use the drugs — which ones, on what types of animal, and in what quantities. This dearth of information makes it difficult to document the precise relationship between routine antibiotic use in animals and antibiotic-resistant infections in people, scientists say.
The scale of the problem became clear in 2010 when the F.D.A. began publishing total pharmaceutical company sales of antibiotics for use in animals raised for human consumption. It turned out that an overwhelming majority of antibiotics produced went to animals, not people.