False Positive: Why the US Diarrhoea Outbreak Source Still Mysterious

Sun Sep 06 2026 14:38:36 GMT+0000 (Coordinated Universal Time)

A false‑positive test on a Taco Bell lettuce sample throws the source of a US diarrhoea outbreak into doubt – here’s what you need to know.

Tests on iceberg lettuce from Taylor Farms, the supplier of Taco Bell, once indicated the parasite Cyclospora linked to an explosive diarrhoea outbreak. The FDA has now re‑examined the sample and declared it a false positive, leaving the real source unknown. Health officials warn against eating shredded iceberg lettuce at Taco Bell locations in several states while investigations continue. Hundreds were hospitalized, but no deaths have been reported. The incident underscores the challenges of detecting food‑borne pathogens and the importance of rigorous testing and recalls.

False Positive: The Real Source Still Unclear

What happened: A sample of iceberg lettuce from Taylor Farms—known supplier for Taco Bell—initially tested positive for the parasite Cyclospora, the suspected cause of the US explosive diarrhoea outbreak.

New FDA findings: The FDA re‑reviewed the sample and ruled it a false positive. The sample was not part of the recent Taylor Farms recall, so the true culprit remains unidentified.

Public health response: Health officials advise diners to avoid shredded iceberg lettuce at Taco Bell in Indiana, Kentucky, Michigan, Ohio, and West Virginia while investigations are ongoing.

Outbreak impact: Over 94 people have been hospitalized, but no deaths have been confirmed. Hundreds of cases surfaced after the first Tyler Farms lettuce lot was linked to the outbreak on 13 May.

What’s happening next: Taylor Farms has halted distribution of lettuce from central Mexico, is working with the FDA and CDC, and has issued a list of recalled products across 27 states.

Remember: If you consume lettuce or salad at Taco Bell and feel unwell—especially with watery diarrhoea that lasts days or sudden weight loss—contact your healthcare provider and report the symptoms.