 The U.S. government reported as many as 20% of all chickens were contaminated with "Salmonella" in the late 1990s, and 16.3% were contaminated in 2005.The United States has struggled to control salmonella infections, with the rate of infection rising from 2001 to 2011.In 1998, the USDA moved to close plants if salmonella was found in excess of 20 percent, which was the industry's average at the time, for three consecutive tests.