The number of cases reported in an E. coli outbreak has increased to 9 confirmed cases and 8 probable, DuPage County health officials said Tuesday.

Six of the nine confirmed cases left people hospitalized, but all have been released, said Jason Gerwig, a spokesperson for the DuPage County Health Department.

The Chicago Tribune reports as part of the investigation, a restaurant in Lombard, Los Burritos Mexicanos, 1015 E. St. Charles Rd., remained closed Tuesday.

Marco Arteaga, manager of the restaurant, said the restaurant is cooperating fully in the investigation. He said the cause of the outbreak is puzzling because none of his employees have been sick, and no problems have been reported at the restaurant’s other locations in Villa Park and St. Charles.

He said all the locations use the same food distributors.