The origins of the current outbreak remain unclear. The U.S. Food and Drug Administration on Saturday said that a sample of shredded iceberg lettuce supplied by Taylor Farms tested positive for cyclospora, only to retract its findings next day.
Reuters reported that FDA on Sunday said laboratory experts re-checked the sample and concluded the finding should be considered a false positive.
Taylor Farms, a California-based lettuce supplier, did not respond to a request for comment but in a statement on its website, it said, "To be clear, at this moment, FDA has not identified a single positive product test result for cyclospora."
The company previously announced it was removing all iceberg lettuce sourced from central Mexico out of an abundance of caution.
If previous cyclospora outbreaks are any guide, the exact origin of the parasite may never be pinpointed. For example, a 2018 outbreak tied to McDonald's salads sickened more than 500 people, but federal investigators never identified a single contamination source.
Two years later, regulators linked another large outbreak to bagged salads sold at Walmart, Aldi and other grocers, but again closed the investigation without determining exactly how the parasite entered the supply chain.
That didn’t stop the lawsuits, however.
Marler’s firm, Seattle-based Marler Clark, represented 30 plaintiffs in suits involving the bagged salads. Those cases settled on confidential terms. The firm also brought similar suits against McDonald’s.
Cyclospora outbreaks can be harder to trace than those caused by bacteria such as E. coli or salmonella, Marler said. In those investigations, public health officials often use whole-genome sequencing to link illnesses to a common source with a high degree of precision.
Becasue cyclospora is a parasite that cannot be routinely grown in laboratories, it's more difficult for investigators to obtain genetic evidence, according to the CDC. As a result, health officials rely more heavily on patient interviews and supply-chain records to track down the source of contamination.
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