Mandernach said there is no immediate threat, so his office is not required to release information about where the product came from. He said state officials believe the affected salad already has spoiled and is no longer in the supply chain.
Nebraska public health officials said they still hadn't traced the exact origins of the outbreaks.
"I am by no means giving all-clear, green light on the issue," said Dr. Joseph Acierno, the state's chief medical officer and director of public health. "We're encouraging the medical community to stay vigilant."
Food-safety and consumer advocates say the agencies shouldn't withhold the information.
"It's not clear what the policy is, and at the very least they owe it to us to explain why they come down this way," said Sandra Eskin, director of the Pew Charitable Trusts' food safety project. "I think many people wonder if this is all because of possible litigation."
Marler said withholding the information can create general fears that damage the reputation of good actors in food production. He said consumers should be allowed to decide for themselves whether to shop and grocery stores or eat at restaurants where tainted produce was sold.
Some states also are slow to interview infected people, he said, which reduces the chances that they remember where they ate.
The Food and Drug Administration said Wednesday that it didn't have enough information to name a possible source of the outbreak. In the past, the agencies have at times declined to ever name a source of an outbreak, referring to "Restaurant A" or using vague terms.
Caroline Smith DeWaal of the Center for Science in the Public Interest says that the decision to withhold a company's name may not only hurt consumers but the food industry, as well. When an item is generally implicated but officials give few specifics, like with the bagged salad, people may stop buying the product altogether.