The maker of a prepackaged salad mix being eyed in an outbreak of cyclospora cannot be named because of a confidentiality law, Iowa health officials said today.

The state's Department of Health identified the mixture of iceberg and romaine lettuce, carrots and red cabbage as the source of a stomach bug that has sickened at least 145 Iowans. But state law requires health officials to "prevent the identification of any business involved in a disease outbreak" unless the information "is necessary for the protection of the public," the department said in a statement.

"Because the vast majority of illnesses occurred in mid-June and the limited shelf life of fresh produce, IDPH [the Iowa Department of Health] and DIA [Department of Inspections and Appeals] determined the implicated salad mix was no longer in the Iowa food supply chain," the department said. "Thus, there is no ongoing threat to the public health which would require the identification of a particular brand, store, or restaurant where the salad mixture was available. In addition, these sites could not have taken any action to prevent contamination of the mixture since it came pre-packaged and ready-to-eat."

The Nebraska Department of Health also tied 78 cyclospora cases to salad mix and has yet to name the manufacturer.

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More than 370 people have contracted the stomach bug in 15 states, according to the U.S. Food and Drug Administration. The source of the infection in states other than Nebraska and Iowa remains unclear. Those states are Texas, Wisconsin, Arkansas, Connecticut, Florida, Georgia, Illinois, Kansas, Minnesota, Missouri, New Jersey, New York and Ohio.

"FDA will continue to work with its federal, state and local partners in the investigation to determine whether this conclusion applies to the increased number of cases of cyclosporiasis in other states," the FDA said in a statement. "Should a specific food item be identified, the FDA, the U.S. Centers for Disease Control and Prevention, state and local partners will work to track it to its source, determine why the outbreak occurred, and if contamination is still a risk, implement preventive action, which will help to keep an outbreak like this from happening again."

Read about how produce is a common culprit in food-borne illness.

Cyclospora, which beyond diarrhea can cause fatigue, weight loss, stomach cramps, vomiting, muscle aches and low-grade fever, can be cleared with antibiotics. But without treatment, the symptoms can linger for months.

People who are "in poor health or who have weakened immune systems" are more likely to have a severe or prolonged illness, according to the CDC.