WASHINGTON – Government investigators are continuing to seek out the source of aSalmonellaoutbreak that has sickened 76 people and killed one California resident, according to The Associated Press. The US Department of Agriculture and Centers for Disease Control and prevention (CDC) believe the outbreak, which has affected people in 26 states is linked to contaminated ground turkey.

These illnesses date back to March. Cultures of ground turkey from four retail locations collected between March 7 and June 27 showed contamination with the same strain ofSalmonella, but CDC couldn't specifically link them to the illnesses, it said on Aug. 1. The preliminary investigation showed that three of those samples were linked to the same factory, but the agency has yet to name the retailers or the manufacturers. Officials must directly link theSalmonellaillnesses with a certain producer or establishment. That's difficult to do because people don't always remember what they ate or where they got it from.

Officials in this case haven't been able to establish a link between theSalmonellasamples they found and the 77 infections. The USDA's Food Safety and Inspection Service sent out an alert about the illnesses late last week telling consumers to properly cook their turkey, which can decrease risks forSalmonella poisoning, but hasn't issued warnings about the source of the infection.

"There is little epidemiological information available at this time that conclusively links these illnesses to any specific product or establishment," said Neil Gaffney, FSIS spokesman. "Without specific enough data, it would not be appropriate to issue a recall notice."

However, the outbreak continues spreading. Michigan and Ohio reported the highest number of illnesses with 10 each, while Texas reported nine. Illinois had seven, California six and Pennsylvania five. Alabama, Arizona, Georgia, Iowa, Indiana, Kentucky, Louisiana, Massachusetts, Minnesota, Missouri, Mississippi, North Carolina, Nebraska, Nevada, New York, Oklahoma, Oregon, South Dakota, Tennessee and Wisconsin are states with at least one illness. Some cases may not have been reported yet.

It can take up to three to four weeks to confirm a single case and identifying an outbreak can take considerably longer than that, the CDC said.