The largest egg recall in U.S. history comes at a point of great consolidation in the egg industry, when a shrinking number of companies produce most of the eggs found on grocery shelves and a defect in one operation can jeopardize a significant segment of the marketplace.

Just 192 large egg companies own about 95 percent of laying hens in this country, down from 2,500 in 1987, according to United Egg Producers, an industry group. Most producers are concentrated in Iowa, Ohio, Indiana, Pennsylvania and California.

“I don’t think people have any idea when they see all these brand names in the stores that so many are coming from the same place,” said Patty Lovera, assistant director of Food and Water Watch, a food safety organization. “It raises the stakes – if one company is doing something wrong, it affects a lot of food.”

Just two Iowa producers, Wright County Egg and Hillandale Farms, have been implicated in a nationwide outbreak of Salmonella enteritidis, with the companies recalling 500 million eggs sold under 24 brands.

As the mega-producers have developed during the past 20 years, they have gone largely unregulated. The Food and Drug Administration had not inspected the two Iowa-based facilities at the heart of the massive recall that began 10 days ago. Nor had the U.S. Agriculture Department or the Iowa Department of Agriculture and Land Stewardship.

“It is shocking that nobody was in these facilities, but it also illustrates that egg laying facilities have fallen into the crack between the government agencies that are responsible for food safety,” said Caroline Smith DeWaal, director of food safety at the Center for Science in the Public Interest.