The victims may have become ill after eating beef produced by JBS Swift Beef Co. of Greeley, Colo., the Centers for Disease Control and Prevention reported. The number of people reported ill so far is 23.
The company recalled about 380,000 pounds of beef on Sunday after some illnesses were reported and a government investigation showed a possible connection to the company's product. That recall expanded a June 24 recall of just over 41,000 pounds.
The CDC said health officials in several states investigating the strain of E. coli found that most ill persons had consumed ground beef, and many reported that it was undercooked. Ground beef with the strain of E. coli was obtained from the home of one person infected.
"At least some of the illnesses appear to be associated with products subject to these recalls," the CDC said in a statement on its Web site.
The first reported illness began on April 2, according to the CDC, and the last on June 13. Wisconsin and Michigan appear to be the hardest hit by the outbreak so far, with six ill people in each state identified by the CDC.
Other cases were reported in California, Maine, Minnesota, New Hampshire, New Jersey, New Mexico and New York.
The CDC did not specify the states in which people were hospitalized. The agency said that two of those who fell ill suffered from hemolytic uremic syndrome, a type of kidney failure.
Kidney failure is found in the most severe cases of E.coli. In less serious cases, the potentially deadly bacterium can cause bloody diarrhea and dehydration.
The outbreak comes on the heels of a recall of Toll House refrigerated cookie dough products and just before the 4th of July holiday, when many Americans are preparing to grill hamburgers outdoors.
Connecticut Rep. Rosa DeLauro, a longtime critic of the food safety system, said this week she is concerned it took too long for JBS Swift to recall the meat. The beef was produced April 21, according to the company and the Agriculture Department.
"It is deeply troubling that it has been over two months since this meat was produced and only now are we learning that thousands of Americans have potentially been exposed to E. coli-tainted beef," said DeLauro, who heads the House subcommittee in charge of Agriculture Department spending. "I urge the USDA to aggressively and expeditiously investigate."
The department's Food Safety and Inspection Service initially took a sample of the beef on May 21 that tested positive for the strain, according to the agency. Because that beef did not enter the food supply, officials did not urge a recall. A follow-up investigation, including information from the illnesses reported, prompted FSIS to go to the company and request the recall, an agency spokesman said.
"Until recently, there was not adequate evidence suggesting a link between this source material and illnesses," said FSIS spokesman Brian Mabry.
In a statement, JBS Swift said it sold the meat as whole muscle cuts and may have been ground by retailers who purchased it. Raw ground beef is considered the highest risk to consumers.
As part of the recall, The Kroger Co. said earlier this week that it is recalling packages of meat with "sell by" dates of April 27 to June 1 in the Cincinnati-Dayton region that includes northern Kentucky and southeastern Indiana; and in western Tennessee, Arkansas, Mississippi, Illinois and eastern Missouri. The company said the suspect beef was sold under its store brands in more than a dozen states.
Kroger-owned Food 4 Less stores in the Chicago area, Fry's stores in Arizona and Smith's stores in Arizona, Utah, and other western states were also included in the recall.
Other grocery retailers are also affected, such as Scarborough, Maine-based Hannaford Supermarkets and Quincy, Mass.-based Stop & Shop. Hannaford has urged customers in Maine, Massachusetts, New Hampshire, New York and Vermont to check freezers for the recalled beef.