Public-health officials in Colorado are investigating three Denver-area Jimmy John’s restaurants for a possible link to an E. coli outbreak that affected eight people, according to local reports.

An epidemiologist with the Colorado Department of Public Health and Environment told local Fox affiliate KDVR that an unspecified produce item served on sandwiches from those restaurants was suspected of causing the outbreak. She added that Jimmy John’s likely was not at fault, as no improper food handling practices have been identified at the three Denver locations, and that the quick-service chain was cooperating fully with the investigation.

The three restaurants have not been closed, since food handling was not a cause of the outbreak.

Jimmy John’s declined to comment for this story.

The eight people stricken with the E. coli 0157 strain of bacteria told officials from the health department, Centers for Disease Control and Prevention, and Food and Drug Administration that they had eaten at Jimmy John’s restaurants between Oct. 5 and Oct. 9. They reported their cases to the health department between Oct. 18 and Oct. 22.

Jimmy John’s has been implicated in previous foodborne-illness outbreaks over the past five years, usually stemming from clover or alfalfa sprouts served on some of their sandwiches. Most recently, the chain was linked to a five-state E. coli outbreak in February 2012 in which 12 people became ill, leading Jimmy John’s to pull clover sprouts from its menu.

Previously, Jimmy John’s customers had been among 88 people sickened in a December 2010 multistate outbreak of salmonella.

Though its main sprout supplier, Urbana, Ill.-based Tiny Greens, did not test positive for salmonella contamination, the supplier and Jimmy John’s nonetheless pulled alfalfa sprouts and sprout mixes from all the chain’s restaurants in Illinois, where approximately half the salmonella cases from that outbreak occurred and “where nearly all of the ill individuals ate sandwiches containing sprouts at various Jimmy John’s outlets,” according to the FDA.

Health department officials also closed a Jimmy John’s location in Boulder, Colo., in October 2008 to investigate the outbreak of 16 severe stomach ailments from people who reportedly ate at that restaurant, nine of whom later were confirmed to have E. coli.

The sandwich chain operated or franchised more than 1,560 locations in the United States at the end of fiscal 2012, according to Nation’s Restaurant News’ Top 100 report.

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