A national outbreak of salmonella was linked on Friday to another major egg producer, Hillandale Farms, prompting the recall of an additional 170 million eggs in 14 states. The latest action -- the third recall announcement in two weeks for eggs -- is bound to shake the confidence of consumers rattled by a succession of food safety scares in recent years, most prominently for foods like beef and lettuce. The idea that half a billion suspect eggs have been circulating in the food supply comes as an embarrassment for the egg industry and federal regulators. New egg safety rules went into effect in July that the Food and Drug Administration had said would prevent tens of thousands of salmonella illnesses a year. Hillandale Farms, one of the nation's largest egg companies, said it was recalling eggs produced at two Iowa sites, in some cases as far back as April. It follows an even larger recall by Wright County Egg, also of Iowa, which recalled 228 million eggs on August 13, and then expanded its recall by an additional 150 million eggs on Wednesday. Hundreds, perhaps thousands, of cases of salmonella since May have been linked to tainted eggs, according to federal health officials. Investigators are continuing to look at the clusters of illness to see whether any other egg producers might be linked to the outbreak. Investigators are also looking at ties between the two egg farms operated in Iowa by Hillandale and the five farms run by Wright County Egg, which is owned by the DeCoster family, a major egg producer. Hillandale said that it bought young birds, called pullets, and feed from a company run by the DeCosters. FDA officials said the chicks used by both farms came from a hatchery that participated in a national program meant to ensure that its chicks were free of salmonella infection. Chickens can get salmonella from rodents in hen houses, from contaminated feed or from workers who may not follow sanitary procedures. Infected hens can lay eggs with the bacteria inside them, and people can become sick if they eat tainted eggs that are not fully cooked. Health experts say that people should make sure that they cook eggs fully to destroy any possible bacteria and wash their hands and utensils after handling raw eggs. Salmonella commonly results in diarrhea, vomiting and stomach cramps. In rare cases, it can lead to more serious conditions, like arterial infections. Even though the recall numbers are large, they represent a small fraction of national egg production, which runs at about 7.5 billion a month. The Wright County eggs have been distributed nationwide. The Hillandale eggs went to 14 states, according to the company: Arkansas, California, Iowa, Illinois, Indiana, Kansas, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, Texas and Wisconsin. They were sold under the brand names Hillandale Farms, Sunny Farms, Sunny Meadow, Wholesome Farms and Werst Creek. 