Federal health agencies and state authorities are investigating one of the largest cyclosporiasis outbreaks in the United States in recent years, with the illness linked to shredded iceberg lettuce served at Yum Brands' Taco Bell restaurants across nine states.

Michigan has emerged as the hardest-hit state, reporting more than 11,000 cases and two deaths as of Monday. State health officials said both individuals who died had significant underlying health conditions that may have been compounded by cyclosporiasis and dehydration.

The U.S. Food and Drug Administration (FDA), Centers for Disease Control and Prevention (CDC), and dozens of state health departments are collaborating on the investigation. The CDC has reported 6,707 laboratory-confirmed cases across 45 states, with 423 patients hospitalized. The agency anticipates the total will rise significantly, as it can take up to six weeks to confirm whether an ill individual is part of the outbreak.

Understanding Cyclosporiasis

Cyclosporiasis is an intestinal infection caused by the cyclospora parasite. According to the CDC, it is contracted by consuming food or water contaminated with feces carrying the parasite. Raw fruits and vegetables are the most common vehicles for transmission.

Symptoms vary from mild to severe. Children, older adults, and individuals with weakened immune systems face a heightened risk of serious illness. While cyclosporiasis itself is generally not fatal and person-to-person transmission is uncommon, untreated infections can persist for weeks and lead to hospitalization, primarily due to dehydration. Deaths from cyclosporiasis are rare in the United States.

The CDC designates the period from May 1 to August 31 as the annual cyclosporiasis season. The U.S. has experienced prior outbreaks tied to fresh produce, including a 2020 multistate outbreak associated with bagged salads that sickened nearly 700 people across 13 states.

Contaminated Produce and the Supply Chain

The FDA's traceback investigation has connected thousands of cases to iceberg lettuce served at Taco Bell restaurants in Indiana, Kentucky, Michigan, Ohio, West Virginia, Illinois, Kansas, Oklahoma, and Pennsylvania.

On July 18, the FDA reported that a sample of shredded iceberg lettuce supplied by Taylor Farms had tested positive for the parasite. The agency retracted that finding a day later after a laboratory review determined the result was a false positive.

Despite the retraction, FDA investigations continue to point toward Taylor Farms. The company has recalled lettuce sourced from central Mexico and shuttered its processing plant in the region. The link between Mexican-sourced produce and cyclospora contamination has surfaced before. In 2013, FDA investigators traced a cyclosporiasis outbreak in Iowa and Nebraska to salad mix produced by Taylor Farms de Mexico that had been served at Olive Garden and Red Lobster restaurants. Two years later, the FDA issued an import alert for cilantro from the Mexican state of Puebla after inspectors documented unsanitary conditions at farms, including human waste in growing fields.

According to the FDA, the recall encompasses Marketside-branded products sold at Walmart, along with dozens of products distributed through Sysco and other companies. The broad scope of the recall reflects the centralized structure of modern produce supply chains, in which a single processing facility can supply products to thousands of retail and restaurant outlets across dozens of states, magnifying the reach of any contamination.

In a July 24 statement, Taylor Farms described the recall as voluntary and asserted it maintains "best-in-class" cyclospora prevention protocols. The company confirmed it is no longer sourcing any iceberg lettuce from the affected region.

Investigations into other potential sources remain ongoing.

Consumer Guidance

The FDA states that cooking produce to at least 158 degrees Fahrenheit (70 degrees Celsius) is the most effective method for killing cyclospora, which is resistant to routine chemical disinfection. The agency also recommends discarding the outer leaves of leafy vegetables and thoroughly rinsing all fruits and vegetables before peeling or consumption.

Past cyclospora outbreaks in the U.S. have been linked to bagged salad mixes and kits, fresh cilantro, basil, raspberries, snow peas, and green onions.

For individuals diagnosed with cyclosporiasis, the CDC recommends treatment with trimethoprim-sulfamethoxazole, an antibiotic commonly sold under the brand name Bactrim. The standard regimen involves taking the medication twice daily for seven to ten days. People living with HIV may require extended treatment.

Disease Surveillance Infrastructure

Cyclospora is classified as a nationally notifiable pathogen. Gwen Biggerstaff, deputy director of the CDC's Division of Foodborne, Waterborne and Environmental Diseases, said most states collect robust data on cases and routinely share that information with the CDC through its disease surveillance system. Healthcare providers in 47 states are legally required to report cyclosporiasis cases to public health departments.

The Foodborne Diseases Active Surveillance Network (FoodNet), a collaboration among the CDC, the U.S. Department of Agriculture, the FDA, and ten state health departments, suspended tracking of six of its eight monitored pathogens last July due to funding cuts. FoodNet, which covers approximately 15% of the U.S. population, had served as a key tool for detecting long-term trends in foodborne illness. Cyclospora was among the pathogens no longer tracked by the network.

Biggerstaff noted that FoodNet's purpose is to observe trends over time and does not replace national surveillance. Participating states continue to report cyclospora cases on a national basis, and the data collection process for this outbreak is consistent with previous ones, she said.