With no disclosure about who could have supplied contaminated meat to a Northeastern chain of grocery stories, the outbreak of Salmonella infection involving ground beef sold by Hannaford supermarkets has been declared over.

In its final investigation update Wednesday, the Centers for Disease Control and Prevention said 20 people in seven states were infected with an antibiotic-resistant strain of Salmonella Typhimurium.

That’s one more case than was reported in the CDC’s Jan. 5 update. “This particular outbreak appears to be over,” the CDC stated.

New Hampshire and New York each reported six outbreak cases, while Maine reported four. Hawaii, Kentucky, Massachusetts and Vermont each reported one individual sickened by the outbreak strain of bacteria.

Their illnesses began around Oct. 8, 2011. The ill people ranged in age from one year to 79 years. Median age was 45. Of 17 ill people with information available, 8 were hospitalized.

The epidemiologic investigation showed that among 19 of the ill people who provided food histories, 14 – or 74 percent – reported eating ground beef in the week before they were sick.  Fourteen of those reported buying the ground beef from Hannaford stores.

Testing by public health labs in New York and Maine isolated the outbreak strain of Salmonella Typhimurium from two different samples of leftover ground beef purchased from Hannaford  supermarkets and collected from unrelated case patients’ homes.

On Dec. 15, when the USDA’s Food Safety and Inspection Service (FSIS) announced the recall of an undisclosed amount of fresh ground beef sold by Hannaford, it said the Scarborough, ME-based grocery chain kept only “limited records,” so that the agency could not determine who had supplied the contaminated beef.

Hannaford regrinds its own beef using meat from several suppliers.

The Portland Press Herald reported Jan. 28 that FSIS plans to close its investigation into the source of the contaminated beef.

Daniel Engeljohn, FSIS assistant administrator, told the newspaper Hannaford ground meat from various suppliers without cleaning the equipment in between batches, which he said raised the possibility of cross-contamination from commingling.

Although there is no requirement that retailers clean grinding equipment between batches of meat from different suppliers, Engeljohn said the USDA recommends it, along with more detailed information about suppliers in grinding logs. He said those recommendations may soon become requirements.

U.S. Rep. Chellie Pingree, D-ME, of Maine, has said that if the USDA does not issue new rules on its own, she will propose legislation mandating it do so.

“We definitely need stricter regulations for large retailers so they are required to keep more detailed records on the ground beef they sell, so it’s possible to track down the source of contamination,” she said in a prepared statement.

CDC Outbreak Map: