Warm weather usually drives salad sales, but consumers spooked by the ongoing cyclospora outbreaks are avoiding lettuce this summer.

Traffic to Chopt Creative Salad Co. locations fell 24% on July 18, right after the Food and Drug Administration announced the outbreak, according to Placer.ai data. Sweetgreen on Thursday said consumer concerns about the outbreak had about a 6 percentage point impact on same-store sales in July, and the company cut its full-year outlook. And earlier this week, upstart chain Salad and Go filed for Chapter 11 bankruptcy and closed all of its locations, saying the cyclospora outbreak had exacerbated its existing business challenges.

Grocery stores aren't immune either. Dollar sales of prepackaged salads plunged 14% during the four weeks ended July 25 compared with the year-ago period, according to NielsenIQ data.

The FDA has pointed to iceberg lettuce processed in Taylor Farms' central Mexico facility as the likely culprit for the outbreak that has sickened at least 10,000 people. Taylor Farms has voluntarily recalled products supplied from that facility.

Yum Brands' Taco Bell is the only national restaurant chain that has been linked to the multistate outbreak. It uses iceberg lettuce frequently across its menu, from its Crunchwrap Supreme to its Cheesy Gordita Crunches, but the chain isn't known for its salads. Taco Bell's sales and traffic to its restaurants initially tumbled after the FDA announcement, but Yum executives said in late July that business was already recovering.

But the FDA is also tracking at least six other active outbreaks without a clear culprit; those outbreaks have significantly smaller number of reported cases. The long incubation period for cyclosporiasis makes it difficult to identify the contaminated ingredients.

Cyclospora is a water-borne parasite. It typically spreads through contaminated produce, like lettuce, green onions, raspberries and fresh herbs. Although public health authorities seem to have pinpointed the source of the current outbreak, the FDA is advising consumers to take extra steps, like discarding outer layers of fruits and vegetables, to reduce risk of exposure.