Steven Mandernach, chief of the Food and Consumer Safety Bureau of the Iowa Department of Inspections and Appeals, said epidemiological data and food history interviews conducted with ill Iowans linked a bagged salad mix with the food-borne illness.
"The evidence points to a salad mix containing iceberg and romaine lettuce, as well as carrots and red cabbage as the source of the outbreak reported in Iowa and Nebraska," Mandernach said in a statement.
"Iowans should continue eating salads as the implicated prepackaged mix is no longer in the state's food supply chain."
However, Mandernach said although Iowa and Nebraska were the first to report Cyclospora illnesses and had the lion's share of cases -- 221 cases -- federal health officials did not know if the rest of the 372 reported cases in 16 states were linked to the same salad mix.
At least 21 individuals reportedly have been hospitalized in three states, the Centers for Disease Control and Prevention in Atlanta said
"Because it can take more than a week for the first symptoms to appear after ingesting the contaminated food, there wasn't a product on the shelf to be examined for the parasite," Mandernach said.
"As a result, most of the food-borne illness investigation focused on trying to trace-back suspected food products through the food chain."
Cases in this outbreak were defined as laboratory-confirmed Cyclospora infection in a person who became ill in June or July, and had no history of travel outside of the United States or Canada during the 14 days prior to onset of illness, the CDC said.
CDC officials said they were notified of 372 cases of Cyclospora infection from the following 16 health departments: Iowa, Texas, Nebraska, Florida, Wisconsin, Illinois, New York City, Georgia, Missouri, Arkansas, Connecticut, Kansas, Minnesota, New Jersey, New York and Ohio.
The Iowa investigation found an exposure to a common prepackaged salad mix from a single source in about 80 percent of the cases.
The investigation was hampered because by the time the one-cell parasitic-induced illness was identified, most if not all of the suspect product was no longer on store shelves, Mandernach said.
"Because it can take more than a week for the first symptoms to appear after ingesting the contaminated food, there wasn't a product on the shelf to be examined for the parasite," Mandernach said. "As a result, most of the food-borne illness investigation focused on trying to trace-back suspected food products through the food chain."
Mandernach noted Iowa received a three-year cooperative grant in 2012 from the federal government to establish a Food and Feed Rapid Response Team. Iowa's public health and regulatory agencies have been working for several years on improving the investigation process for food-borne illness.
"We saw those efforts pay off during this investigation, as all the players worked together seamlessly to the betterment of the public," the food inspector said.