The maker of a widely used laboratory test has suggested that the cyclosporiasis outbreak in the US may be slowing. This outbreak, caused by a single-celled parasite, has grown to more than 18,000 suspected and confirmed cases by late July, marking it as the largest on record for the nation.
The Midwest has been particularly affected, with public health officials connecting infections in nine states to iceberg lettuce sourced from Taylor Farms’ operations in Mexico. The Centers for Disease Control and Prevention (CDC) also noted that cases in at least nine states appeared to be linked.
John Osiecki, vice-president of medical affairs at bioMerieux, a French company that produces a panel testing for 22 gastrointestinal illnesses, expressed confidence in the potential slowdown but stressed the need for continued monitoring. BioMerieux's data, published as Syndromic Trends, shows a decrease in total test positivity. However, this decline could be influenced by increased public awareness leading more people to take tests, potentially pushing down positivity rates even if the outbreak persists.
Despite this caveat, Osiecki remains hopeful that the observed drop is genuine, possibly driven by the same public awareness. He noted hearing people request not to have lettuce due to awareness of cyclospora. In contrast, CDC data, while taking longer to compile, is published with a high degree of certainty. The CDC has confirmed 6,707 cases of cyclosporiasis acquired in the US and is awaiting further data, including interviews, to confirm an additional 11,500 cases.
The test-maker's data indicated that illness involving “parasites” peaked in mid-July with a 15.6% positivity rate. While cyclosporiasis typically increases during summer months, this peak is an outlier compared to the 2.9% parasite positivity rate recorded in the same week in 2025. Further caveats regarding bioMerieux’s data include the panel testing for four parasites, not solely cyclospora, and Medicare only covering the $417 test for immunosuppressed individuals. Tests are also more readily available in urban areas than rural ones.
Food safety researchers have cautioned that the outbreak might be larger than currently known, irrespective of whether it is slowing. The Food and Drug Administration (FDA) is investigating several outbreaks with unknown causes, and the implicated lettuce was sold in 27 states. In New Hampshire, which is not currently considered part of the main outbreak, the state’s health department identified cases linked to Taylor Farms lettuce from Mexico as recently as mid-July, connected to a hospital cafeteria in Keene.