Public health officials in Iowa and Nebraska say they traced an ongoing outbreak of the rare parasite Cyclospora to prepackaged salad mixes. CDC says the stomach bug has sickened at least 372 people across 15 states, including 145 in Iowa and 78 in Nebraska.

Officials in Nebraska say the salad mix contained iceberg and romaine lettuce, red cabbage and carrots, and was sold via national distribution chain. Specific brands have not been named. In Iowa, officials say they have traced 80 percent of cases to a common source which was not identified because it is believed there is no longer a threat to public safety. Steven Mandernach, Iowa's top food safety inspector, says it is possible the parasite spread through contaminated floodwater onto fields in the state.

FDA says it is trying to trace the paths of food eaten by those who fell ill in a process described as "labor intensive and painstaking work, requiring the collection, review and analysis of hundreds and at times thousands of invoices and shipping documents."