Hospitals treated 86 children with similar symptoms in Montgomery, Alabama, this week, prompting worries of an outbreak.
They complained of nausea, vomiting and other digestive troubles, the Department of Public Health said. Thirty children were hospitalized; all but one have been released.
The children all attended two day care centers, which are both served by the same kitchen. The health department has closed the kitchen down, and public health workers have collected clinical and environmental samples for analysis.
The health department has also asked the daycare facilities, which serve about 300 children, to remain closed pending completion of the investigation.
It urged parents not to take sick children who attended the facilities to other daycare providers, and to keep feverish children away from daycare for at least 24 hours after fever has lapsed.