"It's too early to say for sure whether it's over, and thus too early to say there's no risk of still getting sick," said María-Belén Moran, spokeswoman for the Centers for Disease Control and Prevention.
Only Iowa and Nebraska officials had directly linked the outbreak in their states to a salad mix of iceberg and romaine lettuce, carrots and red cabbage.
Heath authorities in California, which provides much of the nation's leafy green produce, said Wednesday the state had not received any reports of cyclospora cases.
"Based on the most currently available information, the leafy greens being implicated in this outbreak were not grown or processed in California," added spokesman Corey Egel in a statement to the Associated Press.
Still, grocery shoppers far from known outbreak areas acknowledged it was a factor as they shopped for produce.
"I can't say I really want to go and buy particularly any lettuce right now," said Laura Flanagan, 35, who was shopping at a Whole Foods in Dallas with her two young children. "I'm being pretty cautious about it."
The product was widely distributed in Iowa by wholesalers who could have supplied the bagged salad mix to all types of food establishments, including restaurants and grocery stores, said Iowa Food and Consumer Safety Bureau chief Steven Mandernach.
Mandernach said at least 80 percent of the vegetables were grown and processed outside both Iowa and Nebraska. He said officials haven't confirmed the origins of 20 percent and may never know because victims can't always remember what they ate.
Iowa law allows public health officials to withhold the identities of any person or business affected by an outbreak. However, business names can be released to the public if the state epidemiologist or public health director determines that disclosing the information is needed to protect public safety.