The Food and Drug Administration found "significant deficiencies" at the Iowa farms implicated in the massive recall. Agency inspectors found the presence of large piles of manure, fly and rodent infestations, and cited significant problems in the producers efforts to mitigate cross-contamination.
The FDA is still investigating the source and cause of the contamination.
Scientific research shows that a complex set of factors influence the risk of infection from Salmonella Enteritidis. These factors include flock size, the presence of rodents, the age of the facility, cleaning methods between flocks, and vaccination rates of chickens.