Federal officials aren’t required to say which restaurants served the tainted hamburger linked to the largest recall of its kind in six years. And they don’t have to tell consumers what type of restaurant dished up meat recalled by Detroit’s Wolverine Packing Co., either — whether it was a sit-down diner or a fast-food joint, according to the U.S. Department of Agriculture’s Food Safety and Inspection Service.

That means no one knows exactly where the approximately 1.8 million pounds of beef covered by Monday’s voluntary recall went after it was produced between March 31 and April 18. FSIS officials first said that the Angus Steak burgers and ground beef patties were sent to four states, but now they’ve expanded the recall to include at least 10 states, with more likely to come, officials said.

On Wednesday evening, FSIS officials said Gordon Food Service Marketplace of Wyoming, Michigan, had sent the meat to nine states: Florida, Illinois, Indiana, Kentucky, Michigan, Ohio, Pennsylvania, Tennessee and Wisconsin. Officials had previously said the meat also went to Massachusetts.

Other distributors included the Surf N Turf Market in Sebring, Florida; Giorgio’s Italian Deli in Stuart, Florida; M Sixty Six General Store in Orleans, Michigan; and Buchtel Food Mart in Buchtel, Ohio.

And it’s not yet clear whether there are more illnesses linked to the ground beef potentially contaminated with E. coli O157:H7, a nasty bacteria that can cause bloody diarrhea and deadly kidney failure, particularly in children and the elderly.

As of late Monday, 11 illnesses were reported in four states, including five in Michigan, four in Ohio and one each in Massachusetts and Missouri, according to the Centers for Disease Control and Prevention. Illnesses began between April 22 and May 2, CDC officials said.

“This strain of E. coli is one of the most hazardous,” said Caroline Smith DeWaal, Director of Food Safety for the Center for Science in the Public Interest. “It’s infrequent that we have a major outbreak from E. coli these days but when it happens, it’s very serious, and it can land quite a number of its victims in the hospital.”

So far, six of 10 victims interviewed by CDC were hospitalized, officials said.

CDC officials said they’re scouring their PulseNet system, which tracks the genetic fingerprints of infections, for more cases that may have been tied to the Wolverine recall. The ground beef was not used in federal Department of Defense programs, the National School Lunch Program or in catalog or Internet sales, officials said. It’s past its use-by date, so there’s little chance it’s still in commerce anyway.

In a statement, Wolverine officials said their products did not test positive for E. coli O157, but CDC and FSIS epidemiological and trace-back data indicate that meat from the firm was the likely source of illness.

The incident underscores the importance of cooking ground beef thoroughly, which kills the bacteria, health officials said. Consumers should make sure to order well-done burgers when eating out.

This is the largest recall of ground beef tied to E. coli O157:H7 since the early summer of 2008, when 5.3 million pounds of meat eventually traced to the firm Nebraska Beef were pulled, followed by another 1.36 million pounds that August. As many as 79 people were sickened, CDC reports showed.