FDA says Taylor Farms lettuce test was false positive in cyclospora outbreak

FDA laboratory experts re-checked a Taylor Farms lettuce sample on July 19 and found the Cyclospora result was a false positive, leaving the source of the parasite still unidentified. The reversal weakened a key clue in an outbreak that health officials tied to fresh produce and that has already sent investigators across multiple states.

The investigation had focused on iceberg lettuce supplied by Taylor Farms, including product served at Taco Bell, after Taylor Farms removed or recalled some iceberg lettuce products from the U.S. supply chain and from 27 states. With the sample now ruled out, the food-tracing trail is even less certain for retailers deciding what to pull and for consumers trying to judge whether the danger has passed.

CDC put the domestic cyclosporiasis outbreak at at least 1,600 confirmed U.S. cases by July 14, and earlier in July the count was 2,944 cases in 32 states. Later tracking pushed the total to nearly 7,000 cases across 34 states, and CDC projected cases could continue to rise through August as states keep reporting new illnesses.

Cyclospora can cause watery or explosive diarrhea, fatigue, abdominal cramps and nausea, and the illness can last for weeks if it is not treated. The parasite is notoriously hard to trace because symptoms may not appear for days, contamination can be intermittent and produce is often distributed widely before investigators can connect cases to a single source.

FDA and CDC have continued the investigation together, but the false positive showed how much uncertainty can remain even after a product appears to match the outbreak pattern. A former FDA outbreak investigator said the work is difficult and warned that cuts to food-safety and public-health funding could slow the response when speed matters most.