False Positive Turns Up: Source of U.S. Diarrhoea Outbreak Still Unknown

Mon Sep 14 2026 08:13:36 GMT+0000 (Coordinated Universal Time)

An FDA test on iceberg lettuce linked to the 94‑hospitalised ‘explosive diarrhoea’ spike turned up a false positive. Authorities still search for the parasite’s source.

The U.S. Food & Drug Administration has announced that a test of an iceberg lettuce sample from Taylor Farms, the supplier of taco‑bell locations, produced a false positive for Cyclospora, the parasite blamed for a recent diarrhoea outbreak. The positive result was re‑reviewed and dismisses the sample as a false positive, but the outbreak’s exact origin remains undetermined. At least 94 people have been hospitalised and there have been no deaths. Taylor Farms has voluntarily removed the implicated lettuce from the U.S. market and the recall covers 27 states, while Taco Bell has removed the product from its restaurants. The CDC advises consumers to avoid shredded iceberg lettuce in several states.

Tests of an iceberg lettuce sample linked to a wave of explosive diarrhoea in the United States returned a false positive for Cyclospora, the parasite responsible for the outbreak, the U.S. Food and Drug Administration (FDA) said on Saturday.

An original test claimed the sample from Taylor Farms – the lettuce supplier for Taco Bell – had tested positive for Cyclospora. However, a re‑review carried out by the FDA concluded that the finding did not represent true amplification and should be considered a false positive.

While the FDA reassured that the recalled product was not part of the sample tested, the exact source of the parasite remains unknown. The outbreak, first detected on 13 May, has left 94 people hospitalised, though no deaths have been recorded. Symptoms can take up to two weeks to appear and include watery diarrhoea, weight loss and loss of appetite.

Taylor Farms voluntarily removed all iceberg lettuce from U.S. markets sourced from central Mexico and has notified customers that it is working with the FDA, CDC and state authorities. The recall covers 27 states and affected Marketside‑branded lettuce sold at Walmart stores in 15 states.

Taco Bell has removed the implicated lettuce from its restaurants and has confirmed that no affected product is currently on menu. The CDC recommends that consumers avoid shredded iceberg lettuce sold at Taco Bell locations in Indiana, Kentucky, Michigan, Ohio and West Virginia.

View of Taylor Farms building with trucks in front of it