The U.S. Food and Drug Administration determined that a lettuce sample previously testing positive for Cyclospora was a false positive.
This finding complicates the ongoing effort to pinpoint the exact origin of the cyclosporiasis outbreak. While a specific laboratory result was overturned, the agency is still working to protect public health by identifying the contaminated product.
The issue involves shredded iceberg lettuce supplied by Taylor Farms. Reports indicate the produce was grown in California, though some sources reference Mexico as the origin. A laboratory error led to the initial positive result, which the FDA corrected after laboratory experts re-examined the sample.
Despite the false positive, the FDA has not changed the existing recall. Agency data continues to support Taylor Farms lettuce as the likely source of the outbreak. The agency said the investigation remains active as it searches for the true source of the parasite.
Dr. David Acheson, a former FDA medical officer, provided context on the situation. Acheson has more than 40 years of medical and food-safety experience [1]. He said the false positive has implications for the broader outbreak investigation.
The FDA announced the re-evaluation on a Sunday. The agency continues to monitor the supply chain to determine why the outbreak is occurring if the specific tested sample was clean.
“The FDA determined that a lettuce sample previously testing positive for Cyclospora was a false positive.”
The discovery of a false positive creates a gap in the direct evidence linking a specific batch of produce to the illness. However, because epidemiological data often outweighs a single laboratory test, the FDA is maintaining the recall. This situation highlights the difficulty of tracing foodborne parasites, where the contaminated product may have already been consumed or discarded by the time testing occurs.
