Paul Ray, Panera’s vice president for sourcing, said there was is a lot of confusion about how extensive the impact on the egg supply would be and sometimes even about where eggs are used in the supply chain — suppliers themselves have suppliers, which in turn have other suppliers.

“Just accumulating information can be difficult — this continues to materialize,” Mr. Ray said. “Two weeks ago, it was an issue but not as significant an issue as it has become in the last 10 days.”

Many companies declined to speak about the indirect impact avian flu is having. Food businesses are notoriously secretive about their suppliers for competitive reasons, and some worry that reports of shortages will somehow raise concerns among consumers. Slightly more than half of consumers surveyed by the NPD Group, a consumer research firm, had concerns about avian flu and its implication for health and food safety — even though the Food and Drug Administration has repeatedly said it is unlikely that eggs in the marketplace would be contaminated in any way, and no chance for harm if eggs are cooked properly.

In a call with analysts on May 8, Robert V. Vitale, chief executive of Post, said the company had a shortfall of about 165 million pounds of liquid eggs.

Less than a week later, three more facilities that supply the company’s eggs — two with flocks that it owns outright and one with flocks owned by a supplier — had been hit with avian flu.

In total, the company has lost one-quarter of its egg supply, which means it cannot fulfill all of its contracts to supply egg products to other businesses. In some cases, Post will have to buy eggs on the spot market to meet its obligations — and Mr. Vitale said in the conference call that the only thing he knew about avian flu for certain was that prices on the spot market would go higher. The company said that Michael Foods, which Post bought last year for $2.45 billion, would discontinue some products and take “appropriate pricing actions to offset reduced egg supply and increased operating costs.”

Egg prices in general are moving up, according the United States Department of Agriculture’s weekly report, and there were not enough liquid eggs available for purchase in the spot market to cover demand last week.