The illness hospitalized at least 26 people and sickened 103.
Four men who own 31 of the area's Subways said they and their employees are suffering financially in the wake of media reports that sometimes fail to point out the measures they've taken to protect the public.
"People need to know it's safe at Subway," said Verne Evans, 72, a Chatham resident and co-owner of 18 Subways in the area.
The Illinois Department of Public Health's investigation of the case continues, spokeswoman Melaney Arnold said last week. The department reported the outbreak June 3.
The state hasn't ruled out the possibility that Subway employees spread the illness; a handful have tested positive for the unusual salmonella strain in the outbreak. The outbreak has been linked almost exclusively to Subway stores in Illinois.
Arnold said investigators are focusing on produce as a potential culprit, though she said a cause isn't known and may never be determined.
A total of 103 people - 101 Illinois residents and two people from outside the state - reported becoming ill and testing positive for the salmonella strain. Those testing positive, including 12 from Sangamon County, ranged in age from 10 days (the infant probably contracted the illness from an adult) to 80 years old.
Twenty-six people, including two from Sangamon County, were hospitalized, but all have recovered, Arnold said.
The statistics may not reflect all the illnesses, she said, noting that federal health officials estimate there can be 38 cases of salmonella for every confirmed case.
Eating food contaminated with animal feces normally transmits salmonella.
At least one lawsuit has been filed against Subway in connection with the outbreak; a Bolingbrook woman claims she got sick after eating a sandwich from a Subway in Will County on May 12.
Arnold said Subway officials have cooperated with the investigation. They voluntarily discarded all produce - lettuce, tomatoes, green peppers and red onions - suspected to be connected with illnesses.
The affected people ate at 49 Subway locations in 28 Illinois counties and one Subway in Minnesota.The 28 counties include Cass, Christian, Macon, McLean, Peoria, Sangamon (four restaurants), Schuyler, Tazewell and Winnebago.
Subway employees, most paid slightly above minimum wage, have seen their hours cut an average of 20 percent to 30 percent by managers who couldn't justify maintaining staffing levels amid the decline in sales, Evans said.
Mark Burris, 58, a Glenarm resident and Evans' business partner, said some employees have told managers that they can't make their rent payments with reduced paychecks.
Arnold said: "We're not trying to damage or hurt Subway's business. Our goal is not to disparage Subway in any way, shape or form. Our business is public health."
'Safest place to eat'
With all the scrutiny from state and local health departments and corporate Subway officials, Subways in Illinois are "probably the safest place to eat in America," said DeWayne Collins, 47, a Riverton resident who owns six area Subways.
Many people eat at Subways, Evans said, so it's not surprising that health investigators have found meals at a Subway between May 5 and June 4 to be a common thread among people who got have tested positive for Hvittingfoss salmonella.
"We kind of figure we're a victim of our own success," Collins said.
The latest positive salmonella tests came in Tuesday, but the dates that those people ate at Subway haven't changed, Arnold said.
Collins said corporate officials from the Connecticut-based chain have told local owners that revenues are down between 30 percent to 50 percent in Peoria, Champaign-Urbana and other areas where media coverage of the outbreak has been extensive.
The outbreak couldn't have come at a worse time - right before summer, traditionally the busiest time of the year for Subways, the local owners said.
Lingering concern among the public is understandable but not warranted, said Springfield resident Mike Orlando, 55, who owns seven Subways.
"Nobody wants to take their family someplace they can get sick," he said.
Workers always wear gloves while they prepare sandwiches in front of the public, and Subways have built a loyal, trusting base of customers, Burris said.
However, fears generated by the outbreak broke customers' habits of regularly visiting Subways near their home or workplace, Orlando said.
"Now we have to win them back," he said.