A testing error by the Food and Drug Administration (FDA) has complicated the investigation into a multistate cyclospora outbreak that has sickened thousands of Americans, even as the outbreak itself continues to spread across the country. On July 20, health officials announced that an initial positive test result for cyclospora in shredded lettuce from Taylor Farms was a "false positive," meaning there are now no confirmed positive sample results tied to the outbreak despite thousands of confirmed illnesses.

The FDA blamed the error on the complexity of detecting the cyclospora parasite, a microscopic organism that causes severe intestinal illness. The agency said it had "apologized" to Taylor Farms and continues working with the company to ensure contaminated products are removed from the market. Despite the testing mistake, the outbreak investigation itself remains active, with more than 5,000 cases confirmed in Michigan alone and 1,645 cases confirmed across 34 states since May 1.

How Did This Testing Error Happen?

The false positive highlights a critical vulnerability in food safety testing: cyclospora is notoriously difficult to detect in laboratory samples. The parasite is microscopic and requires specialized expertise to identify correctly under a microscope. The FDA's admission that its own experts initially misidentified the organism raises questions about the reliability of rapid testing methods when public health is at stake.

The error occurred after the FDA had already linked Taylor Farms de Mexico to the outbreak based on epidemiological evidence, meaning investigators traced illnesses back to people who had eaten lettuce from that supplier. Taylor Farms voluntarily recalled all iceberg lettuce sourced from central Mexico, and Taco Bell stopped using the affected lettuce "indefinitely" after the FDA and Centers for Disease Control and Prevention (CDC) warned customers in five states: Indiana, Kentucky, Michigan, Ohio, and West Virginia.

Why Is Cyclospora So Hard to Detect?

Cyclospora cayetanensis is a parasite that causes an intestinal infection called cyclosporiasis. Unlike bacteria such as E. coli or Salmonella, which can be cultured in laboratory media, cyclospora requires careful microscopic examination and specialized staining techniques to identify. The organism is also present in very small numbers in contaminated food, making it easy to miss during routine testing.

The parasite spreads through feces and typically contaminates produce when farm water supplies contain sewage or when workers handle food without washing their hands after using the bathroom. Once ingested, cyclospora causes explosive watery diarrhea, fever, belly cramps, nausea, and vomiting. Unlike some foodborne illnesses, cyclosporiasis is not transmitted from person to person, but it does last longer than typical food poisoning and symptoms can improve and then return.

"This diarrhea makes you feel terrible. You should be worried if you live in a state where there's a current outbreak. But on a level of worry between one to 10, it's not the 10 or even a nine or eight. I would say just be more aware of the food you're eating," explained Dr. Jade Le, infectious diseases service line chief at Access TeleCare.

Dr. Jade Le, Infectious Diseases Service Line Chief at Access TeleCare

What Does the Outbreak Look Like Right Now?

As of July 17, the CDC had confirmed 1,645 cyclosporiasis cases across 34 states, with 141 people hospitalized and more than 5,100 additional illnesses under investigation. Michigan has been hit hardest, with more than 5,000 cases and 102 hospitalizations. The median age of sick people is 44 years old, with cases ranging from age 5 to 88, and 59% of cases are in women. No deaths have been reported, but the CDC expects the number of cases to rise because cyclosporiasis is often underdiagnosed and underreported.

The median illness onset date is June 18, suggesting that many people became sick in mid-to-late June. The outbreak appears to be linked to lettuce and leafy greens, consistent with past cyclospora outbreaks that have been traced to imported fresh produce including raspberries, basil, snow peas, mesclun lettuce, and cilantro.

How to Reduce Your Risk of Cyclospora Infection

• Wash all produce thoroughly: Rinse fruits and vegetables under running water before eating or preparing them, even if they are labeled "prewashed." This simple step removes most parasites and other contaminants. Do not use bleach or other cleaning agents, which are ineffective against cyclospora and can leave harmful residues.
• Cook produce when possible: Cooking is the most effective way to kill the cyclospora parasite. If you are roasting root vegetables or preparing cooked dishes, heat will eliminate the risk entirely.
• Know your produce source: Locally grown produce may carry lower risk because fruits and vegetables grown abroad are more likely to come from countries with less stringent water safety standards. When eating at restaurants or events, stay informed about outbreaks in your state.
• Practice hand hygiene: Wash your hands with soap and water after using the bathroom and before, during, and after food preparation. This prevents spreading cyclospora if you are infected and protects you from contamination.
• Avoid untreated water: Do not drink or cook with untreated water, especially in areas where outbreaks are occurring. Cyclospora spreads through feces, so water safety is critical.

The main health risk from cyclosporiasis is severe dehydration, which can require hospitalization. However, deaths are rare unless symptoms go untreated for an extended period. Most people recover with supportive care and hydration.

What Does This Testing Error Mean for Food Safety?

The FDA's false positive test reveals a gap in food safety infrastructure: the agency lacks a rapid, reliable method to confirm cyclospora in food samples. While epidemiological evidence (tracing illnesses back to a specific food source) is powerful, it cannot replace laboratory confirmation. The error also underscores why the FDA continues to work with Taylor Farms even though the positive test was wrong; the outbreak itself is real, and investigators are still working to identify the true source.

The complexity of cyclospora detection means that future outbreaks may face similar delays in confirmation. Improving laboratory capacity and training for parasite identification could help public health agencies respond faster and more accurately to contaminated food supplies. For now, consumers in affected states should remain vigilant about washing produce and staying informed about outbreak updates from local health departments and the CDC.