EXPLAINER: What to know about US cyclosporiasis outbreak

The U.S. Food and Drug Administration (FDA), Centers for Disease Control and Prevention (CDC), and dozens of states are investigating a surge in cyclosporiasis cases, an intestinal illness caused by a parasite. Michigan has reported more than 9,000 cases and is searching for possible links beyond the initial cases connected to lettuce.

The outbreak, one of the largest U.S. cyclosporiasis outbreaks in recent years, has been linked to shredded iceberg lettuce served at Yum Brands' Taco Bell restaurants in nine states. Investigations are ongoing to determine whether other food sources may also be involved.

What is cyclosporiasis?

Cyclosporiasis is an intestinal infection caused by the Cyclospora parasite, which can be contracted by consuming food, particularly raw fruits and vegetables, or water contaminated with feces carrying the parasite, according to the CDC.

Symptoms can range from mild to severe and may include diarrhea, stomach cramps, nausea, and fatigue. Children, older adults, and people with weakened immune systems are at greater risk of serious illness.

While cyclosporiasis is not usually fatal, untreated infections can last for weeks and may lead to hospitalization, especially due to dehydration.

The U.S. has experienced previous cyclosporiasis outbreaks linked to fresh produce, including a 2020 multistate outbreak associated with packaged salads that sickened nearly 700 people across 13 states.

The CDC identifies May 1 to Aug. 31 as the annual cyclosporiasis season. Since June 22, the agency has reported 1,947 laboratory-confirmed cases, including 98 hospitalizations. The CDC expects the number to rise because it can take up to six weeks to determine whether an illness is part of the outbreak.

What do we know about the contaminated produce?

The FDA's traceback investigation found a link between thousands of cases and iceberg lettuce served at Taco Bell restaurants in nine states: Indiana, Kentucky, Michigan, Ohio, West Virginia, Illinois, Kansas, Oklahoma, and Pennsylvania.

The FDA initially reported on July 18 that a sample of shredded iceberg lettuce supplied by Taylor Farms tested positive for Cyclospora. However, the agency withdrew the finding the following day after a laboratory review determined that the result was a false positive.

Despite the correction, FDA investigations continue to point to Taylor Farms as a source connected to the outbreak. The company recalled lettuce products from central Mexico and temporarily shut down its processing facility there.

The recall included Marketside-branded products sold at Walmart and other products distributed through Sysco and other companies, according to the FDA.

Taylor Farms said in a July 24 statement that the recall was voluntary and that the company follows strict Cyclospora prevention measures. The company added that it is no longer sourcing iceberg lettuce from the affected region.

How can people protect themselves?

The FDA said cooking produce to at least 158 degrees Fahrenheit (70 degrees Celsius) is the most effective way to kill Cyclospora because the parasite is resistant to routine chemical disinfection.

The agency also recommends removing the outer leaves of leafy vegetables and thoroughly washing fruits and vegetables before peeling or eating them.

Cyclospora is usually spread through contaminated food or water and is not commonly transmitted from person to person.

Previous outbreaks have been linked to packaged salad mixes and kits, fresh cilantro, basil, raspberries, snow peas, and green onions.

For people diagnosed with cyclosporiasis, the CDC recommends treatment with trimethoprim-sulfamethoxazole, an antibiotic commonly sold as Bactrim, taken twice daily for seven to 10 days. People living with HIV may require longer treatment.

What surveillance is being conducted?

Cyclospora is a nationally notifiable pathogen, meaning healthcare providers and public health officials track and report cases across the country.

Gwen Biggerstaff, deputy director of the CDC's Division of Foodborne, Waterborne, and Environmental Diseases, said most states collect and share cyclosporiasis data with the CDC through its disease surveillance system.

Healthcare providers are required to report cases of cyclosporiasis to public health departments in 47 states.

The Foodborne Diseases Active Surveillance Network (FoodNet), a collaboration between the CDC, U.S. Department of Agriculture, FDA, and 10 state health departments, previously tracked Cyclospora cases. However, last July, it stopped monitoring six of eight pathogens, including Cyclospora, due to funding cuts.

Biggerstaff said FoodNet is designed to monitor disease trends over time and does not replace national surveillance. States continue to report Cyclospora cases nationally, and the data collected for the current outbreak is consistent with previous outbreaks. -Reporting by Siddhi Mahatole, Padmanabhan Ananthan, Mariam Sunny and Sneha S K in Bengaluru and Tom Polansek in Chicago; Editing by Caroline Humer, Matthew Lewis, Jamie Freed and Deepa Babington/Reuters