But the efforts were patchwork. For example, Iowa, where Mr. DeCoster has five farms tied to the current outbreak, required no testing.

And the federal government, at times under pressure from Congress and the industry to limit regulation, spent two decades debating national egg safety standards. New rules finally went into effect in July  too late to prevent the current round of illness.

Records released by Congressional investigators last week suggest that tougher oversight of Mr. DeCoster’s Iowa operations might have prevented the outbreak, which federal officials say is the largest of its type in the nation’s history, with more than 1,600 reported illnesses and probably tens of thousands more that have gone unreported.

According to the records, Mr. DeCoster’s farms in Iowa conducted tests from 2008 to 2010 that repeatedly showed strong indicators of possible toxic salmonella contamination in his barns. Such environmental contamination does not always spread to the eggs, and it is unclear what actions Mr. DeCoster took in response. However, when the Food and Drug Administration inspected the farms after the recalls, officials found unsanitary conditions and the presence of Salmonella enteritidis in barns and feed.

“It’s striking that he was part of the early phase of the epidemic and that there is now a problem on his farms in Iowa,” said Dr. Robert Tauxe, deputy director of the foodborne illness division of the Centers for Disease Control.

Mr. DeCoster, also known as Jack, is expected to testify on Wednesday before the House Subcommittee on Oversight and Investigations, which is looking into the outbreak.

He has declined repeated requests for an interview since the egg recall began in August. But Hinda Mitchell, a spokeswoman, said in an e-mail that his farms have always “fully complied with the investigation and the orders from the states to address these situations.”