Investigators have traced the source: contaminated shredded lettuce.

The US Food and Drug Administration confirmed on Thursday that shredded iceberg lettuce delivered to Taco Bell outlets in five states fueled the ongoing cyclosporiasis outbreak.

According to the FDA the implicated lettuce served at restaurants in Indiana Kentucky Michigan Ohio and West Virginia accounted for 1644 confirmed cases of the illness.

While the agency did not identify the supplier by name its probe pointed to one iceberg lettuce provider from Mexico that supplied the affected Taco Bell sites where patrons fell ill.

A source with knowledge of the situation indicated the supplier was Taylor Farms.

Officials note the actual tally of infections this summer is probably far greater and the outbreak extends past Taco Bell lettuce supplies.

Cyclospora cases have appeared in 34 states since May 1 the Centers for Disease Control and Prevention reported. By July 13 authorities recorded 1645 confirmed illnesses and 141 hospitalizations with no deaths linked so far.

Michigan alone logged over 4300 cases prompting state health officials on Monday to flag lettuce or salad greens as a likely contamination source.

Taylor Farms offered no comment on the cyclospora issue despite repeated inquiries. Its recall page showed no active product recalls as of early Friday.

Taylor Farms stands as a leading worldwide lettuce provider to restaurants and retailers

The company produces more salad than any other firm globally and counts Chipotle McDonalds Costco Walmart and Trader Joes among its clients. It runs 30 processing plants throughout North America. It remains unclear if the current outbreak involves only chopped lettuces or additional items and labels.

Taco Bell announced Thursday evening that after discussions with health officials and as a precaution it had voluntarily pulled potentially affected lettuce from a supplier in select states. The ingredient was removed indefinitely from the nationwide supply chain and slated for replacement within 24 hours in impacted areas.

Experts advise steering clear of bagged lettuce and salads while the outbreak persists. They suggest opting for whole heads removing outer leaves and washing produce thoroughly. No washing method reliably eliminates cyclospora so cooking items to at least 158 degrees Fahrenheit offers the best protection.

The parasite flourishes in summer warmth. CDC deputy director Gwen Biggerstaff noted Tuesday that cases could keep rising possibly until the end of August when the cyclosporiasis season concludes.

Watery diarrhea marks the primary symptom of infection

Those affected this summer have reported watery diarrhea along with cramping and gas. Untreated the condition may persist for weeks. The antibiotic combination Bactrim provides effective treatment.

Pre-washed salad kits and bagged greens from multiple brands have surfaced as frequent cyclospora sources in prior years. Outbreaks have also involved other produce such as raspberries snow peas and herbs like cilantro.

Tracing these incidents proves difficult because symptoms emerge after roughly a week making it hard to identify the exact meal responsible. The parasite features more intricate genetics than pathogens such as E. coli or salmonella further complicating investigations.

George Mason University professor Amira Roess a former CDC disease detective suggested contamination likely occurred during washing at processing sites or on the farm.

Contaminated water typically introduces the parasite to produce she explained. While US drinking water stays largely free of such organisms the produce contacts environmental waters that carry the contamination.

Taylor Farms has faced prior recalls involving onions and salad kits

The supplier has dealt with several recalls in recent years.

In 2024 Taylor Farms withdrew yellow onions including some shipped to McDonalds over possible E. coli risks. That outbreak resulted in one death and more than 100 illnesses across multiple states per CDC data.

A 2020 recall targeted onions sold at Kroger and Walmart some tainted with salmonella the FDA stated.

The firm also recalled mislabeled items last year when salad kits failed to note soy and sesame content according to the FDA.