The only hint: items served with fresh tomatoes. Doctor David Acheson with the FDA says being more specific without more evidence would be "irresponsible."
The outbreak is continuing weeks longer than food-poisoning experts had expected.
Disease detectives are exploring whether tomatoes and other produce are sharing a common packing or shipping site where both might become contaminated, or whether multiple foods might be tainted while being grown on adjoining farms or with common water sources.