Federal investigators have not determined the source of contaminated meat that led Hannaford Supermarkets to issue a recall late Thursday of all ground beef with a sell-by date of Dec. 17 or earlier.

An outbreak of infection from a rare strain of salmonella sparked an investigation by the Centers for Disease Control and Prevention and the U.S. Department of Agriculture.

The USDA’s Food Safety and Inspection Service said Hannaford’s “limited records” are hindering its ability to determine the supplier responsible for the contaminated meat.

Ten of the 14 people infected, including four from Maine, said they bought ground beef from Hannaford stores between Oct. 12 and Nov. 20, according to state epidemiologist Dr. Stephen Sears. Seven of the 10, including two from Maine, were hospitalized.

The four Maine residents infected were from Cumberland, York, Androscoggin and Waldo counties, said Sears. He said one of them was hospitalized for four days and another was hospitalized for two days.

“They’re all doing fine,” he said.

Hannaford, which is based in Scarborough and has stores in five states, is the only grocery chain to issue a recall as a result of the salmonella outbreak. The USDA would not say whether there’s a possibility that the contaminated meat could have been supplied to other retailers.

Hannaford has not determined the amount of meat involved in the recall, but will refund any ground beef within its scope, regardless of whether it’s still in its package, said spokesman Michael Norton. The recall covers Hannaford, Taste of Inspirations and Nature’s Place labels.

Norton said suppliers deliver boxes of meat to two Hannaford distribution centers in South Portland and Schodack, N.Y. From there, the meat is delivered to Hannaford’s 179 stores in Maine, New Hampshire, Massachusetts, New York and Vermont. It is ground in the stores, he said.

Norton said Hannaford supplies groceries wholesale to about 30 independent stores, but did not know how many of those stores buy ground beef from Hannaford.

Norton deferred questions to the USDA about where in the supply chain the contamination occurred. USDA spokesman Neil Gaffney declined to comment on the suspected site of contamination, because the investigation is ongoing, he said.

Although the USDA pointed to Hannaford’s record-keeping as an impediment to the investigation, Norton said the grocery chain is “following industry practice and standards in terms of records.”

A lack of record-keeping requirements often makes tracing the source of foodborne illnesses difficult, said Barbara Kowalcyk, founder of the nonprofit Center for Foodborne Illness Research and Prevention. When a source cannot be determined, it’s also difficult to know where a contaminated product ends up, she said.

“Sometimes it starts out small and then two weeks later it gets bigger,” said Kowalcyk. She referred to a massive recall of ground beef in 2002 as an example of a rolling recall.

Kowalcyk’s group is an advocate for greater record-keeping requirements in the industry, as well as for the USDA to have the authority to mandate recalls.

Hannaford characterized its ground beef recall as voluntary in a press release issued just before midnight on Thursday. According to Kowalcyk, all recalls of food products regulated by the USDA are voluntary.

The USDA’s Food Safety and Inspection Service can only recommend a recall, according to the department’s website.

“They could have done nothing,” said Kowalcyk, although she acknowledged it was “in the company’s best interest.”

Norton said Hannaford has been talking to federal investigators for the past couple of days, but they didn’t determine there was a connection between the company the contaminated meat until Thursday. That night, Hannaford removed all ground beef with a sell-by date of Dec. 17 or earlier from its shelves, said Norton.

The scope of the recall, which Norton called aggressive, was decided through a collaboration between Hannaford and the USDA, he said.

The Hannaford stores that were linked to illnesses were in Maine, New York, New Hampshire and Vermont, according to the USDA.

Other states that received reports of illness involving the rare strain of salmonella, which is resistant to common antibiotics, were Ohio, Kentucky and Hawaii, said Sears, the epidemiologist. The cases were reported between Oct. 16 and Nov. 27. The first case in Maine was reported on Oct. 22, he said.

Sears said the Maine Center for Disease Control and Prevention investigates all cases of salmonella and enters them into a national database, which is how the connections were made among the cases in different states.

Common symptoms of salmonella include diarrhea, abdominal cramps and fever within 12 to 72 hours of consuming contaminated food, according to the USDA. Other symptoms are chills, headache, nausea and vomiting and can last for up to a week. Salmonella infection can be life-threatening, especially for people with weakened immune systems, including infants, the elderly and people with HIV or who are undergoing chemotherapy.

The USDA urges people only to eat ground beef cooked to a temperature of 160 degrees and confirm the temperature with a food thermometer.