The CDC published a statement this week, noting that investigative work was continuing into Salmonella Heidelberg infections that are likely to be related to Foster Farms chicken.
Between 1 March 2013 and 22 May 2014, a total of 574 people infected with seven outbreak strains of Salmonella Heidelberg have been reported from 27 US states and Puerto Rico, with 77% of those infected in California.
The manufacturer said that, since October 2013, it has been using a "multiple-hurdle approach" to reduce or eliminate salmonella at each stage of its production.
It said that, as a result, the company continued to make steady progress and has effectively reduced salmonella at the parts level to less than 10% – well below the 2011/2012 USDA-measured industry benchmark of 25%.
According to the CDC, epidemiologic, laboratory, and traceback investigations, conducted by local, state and federal officials, have indicated that consumption of Foster Farms brand chicken is the likely source of this outbreak of Salmonella Heidelberg infections.
It said the outbreak strains are resistant to several commonly prescribed antibiotics.
According to the Natural Resources Defense Council (NRDC), statements from Foster Farms suggest it relies on antibiotics to keep its chickens alive - "a practice that is known to breed antibiotic resistant bacteria".
It has said that poultry producers can and should rely on improved sanitation, reduced crowding, better breeding, vaccinations, improved nutrition and other best practices, to guard against illness.
The NRDC has also called for Foster Farms to disclose its antibiotic use and publicly commit to only use medically important antibiotics to treat sick birds and never for routine, nontherapeutic purposes.
At a recent US Poultry and Egg Association poultry processor workshop, Dr Dan Zelenka, director of statistics, Tyson Foods, said there was "no silver bullet" for removing pathogens in poultry.
He reviewed various types of interventions and stressed that the USDA would continue to put pressure on the poultry industry to lower pathogen contamination rates.