UPDATE: Investigation continues in US egg recall

A potential source of the salmonella that tainted shell eggs from two companies and started a nationwide egg recall remains under investigation, according to CNN.
Bacteria have been found in chicken feed and in barns and walkways at Wright County Egg and Hillandale Farms, the two companies in the middle of the recall. According to federal investigators, contamination likely happened at some point after the feed or feed ingredients went through the heat treatment that kills salmonella. The feed was produced at a Wright County Egg mill and given to pullet chickens at both companies. The exact cause of contamination has not yet been determined, and federal officials are not ruling out the possibility of other sources. Investigators are not yet prepared to release inspection findings, calling any conclusions that might be drawn "a little premature" at this point, but some results may be released later this week. Food and Drug Administration (FDA) Commissioner Margaret Hamburg did say the farms involved in the recall fell short of safety standards.
Wright County Egg and Hillandale Farms have now recalled over half a billion shell eggs between them. The Centers for Disease Control and Prevention (CDC) reported that 2,403 cases of Salmonella enteritidis were recorded from May 1 to August 25, as opposed to the 933 cases that would normally be reported during that timeframe. Federal officials said they do not expect any more recalls.
The Wright County Egg recall specifically relates to eggs packed between May 16 and Aug. 13, with Julian dates ranging from 136 to 229 and plant numbers 1026, 1413, 1720, 1942 and 1946. Brand names include: Cardenas, Trafficanda, Lucerne, Sunshine, Hillandale, Trafficanda, Farm Fresh, Shoreland, Dutch Farms, James Farms, Glenview, Mountain Dairy, Ralphs, Boomsma, Lund, Kemps and Pacific Coast. Affected eggs were distributed to food wholesalers, distribution centers and foodservice companies in California, Arizona, Missouri, Minnesota, Texas, Georgia, Washington, Oregon, Colorado, Nevada, Iowa, Illinois, Utah, Nebraska, Arkansas, Wisconsin and Oklahoma.
The Hillandale Farms recall covers eggs distributed under the brand names Hillandale Farms, Sunny Farms and Sunny Meadow sold between April and August. Hillandale said the eggs were distributed to grocery distribution centers, retail groceries and food service companies that serve or are located in 14 states: Kansas, Arkansas, California, Iowa, Illinois, Indiana, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, Texas and Wisconsin.
A complete list of affected eggs is available through the Egg Safety Center.