A lettuce sample from Taylor Farms that had tested positive for cyclospora did not actually contain the parasite, the Food and Drug Administration announced Sunday. The agency said laboratory experts re-reviewed the results and determined the finding was not valid.
"Due to the complexity in detection of Cyclospora, FDA laboratory experts re-reviewed the sample results and have concluded that the finding does not represent true amplification and should be considered a false positive," the FDA said.
The agency also said that as of Sunday it had not found any confirmed positive sample results for product testing for the parasite.
According to CBS News, Taylor Farms had announced Friday that it was voluntarily removing iceberg lettuce sourced from central Mexico after it was linked to one of the largest cyclosporiasis outbreaks in the United States in recent years. The company said the FDA traceback was pointing to a specific independent farm that represents less than 1% of the country's iceberg lettuce supply, and that it had removed all iceberg lettuce from the region indefinitely.
After the false positive announcement Sunday, Taylor Farms said: "Our thoughts remain with everyone who has fallen ill in this outbreak. We are committed to working with public health authorities as the ongoing outbreak investigation continues."
The outbreak was first reported in May and has spread to 34 states, sickening more than 1,600 people according to CDC figures. State health departments have reported higher numbers. Michigan's Department of Health and Human Services alone reported more than 5,000 confirmed cases as of Friday. No deaths have been reported.
The CDC identified lettuce supplied to select Taco Bell restaurants as a source of the outbreak on Thursday. The iceberg lettuce was distributed to Taco Bell locations in Indiana, Kentucky, Michigan, Ohio and West Virginia. Taco Bell said Friday it had completed removal of affected Taylor Farms lettuce from its restaurants.
Walmart also pulled four Marketside bagged iceberg lettuce salad products from stores in more than two dozen states over the weekend, though the company said there was no indication that its products were connected to the current investigations.
Cyclosporiasis is caused by the cyclospora parasite and produces long-lasting, watery diarrhea. Outbreaks typically occur in late spring and summer and have historically been linked to bagged salads, cilantro, basil, raspberries, snow peas and green onions.