Cyclospora is doing a number on American's stomachs, and on visits to some restaurant chains.

Placer.ai, which analyzes foot traffic at businesses, estimated that visits to U.S. Taco Bell locations Wednesday through Friday last week were down between 16.9% and 18.9%, compared with the day-of-week average between Jan. 1 and July 6.

Other chains that typically use fresh produce also saw slower traffic. Chipotle's visits fell as much as 6.9% over the period, while Panera's traffic dropped by as much as 6.6%, Placer.ai said.

Taco Bell has said that it immediately took action to remove lettuce from its Taylor Farms supplier when it was notified the greens were possibly linked to cyclospora cases. Chipotle said Monday that it doesn't believe its ingredients are associated with the outbreak and it continues to follow the matter closely. Panera hasn't had to remove ingredients due to the outbreak so far, according to the company.

The Food and Drug Administration on Monday walked back an earlier statement that a sample of lettuce from Taylor Farms tested positive for cyclospora, but said that tests on ingredients pulled from markets continue.