Seven NATO officials staying at the Hyatt Regency McCormick Place hotel were being treated Monday after being stricken with flu-like symptoms, law enforcement sources said.
Officials were looking into whether the incident was due to food poisoning, the Sun-Times is reporting.
A U.S. Secret Service spokesman said he believed that seven people were stricken and were being treated but referred other questions to the NATO delegation.
A spokeswoman for the Hyatt Regency McCormick Place said the hotel was alerted Monday that "several" hotel guests complained of feeling ill.
"We have provided them with access to medical attention and are taking appropriate steps to ensure their comfort and safety," Lori Alexander said. "The cause of their illness is not yet determined and is being investigated."