A number of doctors are beginning to express concerns about the growing incidence of antibiotic resistant strains of bacteria in humans. Much of this proliferation is believed to be the result of the widespread use of antibiotics in livestock as a preventative measure in response to the overcrowded and often unsanitary conditions that the animals are often kept in. According to the Worldwatch Institute’s 2006 State of the world report, 74 percent of the world’s poultry, 43 percent of beef, and 68 percent of eggs are now produced this way.