Three cases of salmonella reported earlier this year in South Dakota are of the same strain that led to a recall of 36 million pounds of ground turkey.
Two of the cases were reported in Minnehaha County in March, the other in Brookings County in May, according to information from the South Dakota Department of Health. Two of the people who got sick were women; the other was a man. All three were between 28 and 31 years old, and none died, according to state officials.
Only one of the people indicated he or she ate turkey, according to the Department of Health. No meat was provided for testing.
Nationwide, the first sickness was in March, and the first signs of a salmonella outbreak appeared in May. Two months later, investigators linked the outbreak to ground turkey and a Cargill meat processing plant in Springdale, Ark.
On Wednesday, almost five months after the first illness, the Agriculture Department asked Minnesota-based Cargill to recall the turkey, saying the meat was linked to a death in California and at least 77 illnesses.
Tracking down the source of an illness is a difficult, complicated business, and federal officials defended the months-long process Thursday by saying they wanted to be absolutely sure before they asked Cargill to initiate the third-largest meat recall in history.
''There was an aggressive and thorough investigation that came together over time to paint one picture of this outbreak,'' said Dr. Christopher Braden, an epidemiologist at the federal Centers for Disease Control and Prevention, which investigated the outbreak with the Agriculture Department.
Braden and David Goldman of the USDA's Food Safety and Inspection Service said at a briefing Thursday that authorities weren't sure about the source of the outbreak until July, when they identified it through shopper's card information from victims who had purchased the Cargill turkey, and a leftover sample of turkey from a victim's home. Previous evidence from the investigation had pointed not just to Cargill, but other companies as well, they said.
Less conclusive evidence had pointed toward the Cargill plant in Arkansas, much earlier, however. Samples of Cargill ground turkey purchased at four retail locations as part of routine testing between March 7 and June 27 showed contamination with the same strain of salmonella, though those samples were not specifically linked to the illnesses. Routine salmonella testing in 2010 also showed the pathogen at the plant.
Part of the difficulty for investigators is that USDA rules make it harder to investigate and recall salmonella-tainted poultry.
Because salmonella is so common in poultry, it is not illegal for meat to be tainted with the pathogen. General guidance to consumers is to cook ground turkey to 165 degrees and to handle it properly before it is cooked. If it is cooked and handled properly, it is safe.
Braden and Goldman warned consumers to check their freezers for the contaminated products because frozen ground turkey has a long shelf life. The recall involves fresh and frozen ground turkey products produced at the company's Springdale, Ark., plant from Feb. 20 through Aug. 2.
All of the packages recalled include the code ''Est. P-963,'' according to Cargill, though packages were labeled under many brands. Many of the recalled meats are under the label Honeysuckle White.
The CDC estimates that 50 million Americans each year get sick from food poisoning, including about 3,000 who die. Salmonella causes most of these cases, and federal health officials say they've made virtually no progress against it.
The most common symptoms of salmonella are diarrhea, abdominal cramps and fever within eight to 72 hours of eating a contaminated product. It can be life-threatening to some with weakened immune systems.
The Associated Press and reporter Scott Waltman contributed to this report.
