The salmonella outbreak began in May, when several states began seeing an increase in the number of cases of a common type of bacterial illness known as Salmonella Enteritidis, said Dr. Christopher R. Braden, acting director of food-borne diseases at the Centers for Disease Control and Prevention in Atlanta. The numbers continued to grow, and in June and July, a database used to track disease nationwide found that the number of cases had risen from a historical average of about 50 a week to about 200.

Public health officials in California, Minnesota and Colorado determined that many of the people who had gotten sick had eaten food containing eggs. Further investigation traced many tainted eggs to Wright County Egg.

The company announced on Friday that it was recalling 228 million eggs that it had sold since mid-May. On Wednesday, it added another 152 million eggs to the recall. Many of the affected eggs have long since been cooked and eaten, but millions could still be stored in refrigerators.

The company said the recalled eggs came from five plants and were distributed across the country under the brand names Lucerne, Albertson, Mountain Dairy, Ralph’s, Boomsma’s, Sunshine, Hillandale, Trafficanda, Farm Fresh, Shoreland, Lund, Dutch Farms, Kemps, James Farms, Glenview and Pacific Coast. (Dutch Farms said Wright County packaged eggs under its brand without permission.)

The recalled eggs are packed in varying sizes of cartons, including six-egg, dozen-egg and 18-egg cartons, and loose eggs for institutional use and repackaging, the Food and Drug Administration said. The cartons have date codes stamped at one end, ranging from 136 to 229 and plant numbers 1026, 1413, 1720, 1942 or 1946. The F.D.A. said the plant number is preceded by the letter P, followed by the date code, and showed an example on its Web site.

Consumers were told to return the eggs to stores.

Dr. Braden said that it was not yet possible to say how many people had fallen ill in the outbreak although it certainly numbered in the hundreds. Typically in salmonella outbreaks, only about one in 30 cases is reported to authorities, he said, so thousands of people may have been affected. He said there were no reports of deaths.

Salmonella can cause diarrhea, vomiting and stomach pains. In rare cases, it can cause more serious illness, including arterial infections.

The pathogen is transferred to eggs by infected hens and it can be found inside eggs that appear normal. The bacteria is destroyed by heat but people can become sick if they eat raw or incompletely cooked eggs. Federal regulators have grappled with the problem of salmonella in eggs since it first emerged in the 1980s. But proposals to improve regulations were largely unsuccessful until a year ago, when the Food and Drug Administration announced a new set of rules, which became effective on July 9.

The rules initially apply to egg producers with 50,000 or more laying hens, a category that federal officials said included Wright County Egg. The rules require producers to establish measures to control rodents that can pass salmonella to hens and to prevent contamination by workers or equipment. They also establish testing requirements for poultry houses and eggs.

In a news release on July 9, the F.D.A. said that the rules would prevent as many as 79,000 illnesses and 30 deaths a year related to the consumption of tainted eggs.

Dr. Braden said that investigators looking into the outbreak found cases in which restaurants had used raw eggs in a salad dressing or mixed raw eggs into soup. A case in California in May was traced to a catered event where people had eaten profiteroles containing a custard made with eggs, according to officials in that state.

Hinda Mitchell, a spokeswoman for Wright County Egg, said that the company had put the required federal measures in place by the July deadline. She said that before that date, the company had participated in a voluntary industry program that included steps similar to some of the new federal requirements.

Mr. DeCoster is well known to federal regulators.

In 1997, one of his companies agreed to pay a $2 million fine by the Occupational Safety and Health Administration for violations in the workplace and worker housing. Officials said workers were forced to handle manure and dead chickens with their bare hands and to live in trailers infested with rats. The labor secretary in the Clinton administration, Robert B. Reich, called Mr. DeCoster’s operation “an agricultural sweatshop.”

Mr. DeCoster’s facilities have also been periodically raided by immigration officials. In 2003, Mr. DeCoster pleaded guilty to charges of knowingly hiring immigrants who were in the country illegally and he paid more than $2 million as part of a federal settlement.

Mr. DeCoster was also charged by Iowa authorities in the 1990s with violations of environmental rules governing hog manure runoff.

Ms. Mitchell said that Mr. DeCoster was not available for an interview.

People for the Ethical Treatment of Animals used the recall to press its case for vegan diets, sending an e-mail on Sunday to two million followers that said “half a billion eggs recalled and counting — each egg represents 34 hours of total hell for a hen,” a reference to the average time between egg output. Recipients were asked to urge their friends to view videos starring Paul McCartney and Alec Baldwin that decry the cruelties of egg production.

But the link between cage farming and disease is not so clear, say many academic and government experts who add that some aspects of cage production, which prevents birds from wallowing in their droppings, may be safer than letting hens run loose.

“Some groups tend to cherry-pick studies to show the results that they want consumers to see,” said Jeffrey D. Armstrong, dean of agriculture and natural resources at Michigan State University.

“The bottom line is we don’t know” whether caged or cage-free production is safer, Mr. Armstrong said.

By any historical measure, American egg production is efficient and comparatively safe. The current recall is the largest in memory, but involves only a small fraction of the 70 billion eggs produced annually, mostly by hens who spend their lives with six or seven others in cages the size of an open newspaper, their droppings carried away by one conveyer belt while the eggs are whisked off by another.

Modern egg farms take elaborate steps to keep germs out of barns. But the persistence of salmonella in eggs has been a major concern of health agencies.

The problem of salmonella on eggshells was largely solved in the 1970s, when regulations required the washing and inspection of eggs. In the 1980s, a more insidious threat was recognized: infected hens passing the pathogen to eggs still in formation.

One challenge is the size of farms and flocks today. A single barn may house more than 150,000 birds in tight proximity, allowing infections to spread quickly and widely.

In July, the F.D.A. started requiring large farms to improve refrigeration and do more disease testing, steps it said would reduce salmonella infections by more than half.

Critics still say the cages producing 95 percent of American eggs will remain more dangerous than alternatives.

“The latest science and the best science very clearly show elevated risk in caged facilities,” said Dr. Michael Greger, director of public health and animal agriculture for the Humane Society of the United States, who contested the assertion that he was “cherry-picking” the evidence.

Some experts say the science Dr. Greger cites does not clinch his case, in part because many of the studies, which were mainly done in Europe, compared older, more vulnerable caged facilities with new cage-free barns. One expert review this summer said the evidence was inconclusive.

Egg producers have watched in dismay as the political winds seemed to turn, largely because of growing concern about animal rights. The European Union will bar small cages for egg hens as of 2012. By public referendum, California will ban small cages in 2015, and the state will not allow the sale of eggs produced that way in other states. Michigan, Ohio and other states have placed limits on future caging of hens.

Aimed to prevent such large scale outbreaks, the F.D.A. and U.S.D.A. will now both oversee egg production, which will "prevent each year approximately 79,000 cases of foodborne illness and 30 deaths caused by consumption of eggs contaminated with the bacterium Salmonella Enteritidis," according to the U.S.D.A. If successful, this would be a nearly 60 percent reduction in egg-related salmonella illnesses.

Thus far, two major egg producers have issued a national voluntary egg recall, including Wright County Egg and Hillandale Farms, both of Iowa and both suspected sources for the contaminated egg inventory. In a television interview on August 22, commissioner of the F.D.A., Margaret Hamburg, expressed suspicion that these farms were not in compliance with F.D.A. Standards. Whether through oversight or a gap in evaluation between the two agencies, the fact remains that both failed to prevent such missteps before contaminated eggs reached consumers.

Upon the new ruling on July 9, Hamburg expressed confidence in the renewed food safety framework: "Preventing harm to consumers is our first priority. Today's action will help prevent thousands of serious illnesses from Salmonella in eggs."