The source of the outbreak of Salmonella at Illinois Subway restaurants in late April and June may have been a food distributor in the central part of the state, authorities said Thursday.

In a final, 69-page report on the outbreak, the Illinois Department of Public Health said it could not identify the exact source of the problem, but that the “most likely source” of the lettuce, tomatoes and olives linked to the illnesses was Lincoln-based Sysco Central Illinois Inc., which delivered produce to the affected restaurants.

More than two dozen people were hospitalized in the outbreak, which included 109 confirmed cases and more than 90 probable or suspected cases.

The report said 49 restaurants in 28 central and northern Illinois counties were connected to the outbreak.  More than 480 workers at the stores had to be tested; a dozen of them were found to be positive for the Hvittingfoss strain of Salmonella.