Is the cyclosporiasis outbreak slowing? Test-makers are hopeful

Data by one test-maker shows a positivity drop, but rate could be influenced by number of people taking test

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The maker of a popular laboratory test said the cyclosporiasis outbreak in the US may be slowing. An outbreak of infections from the single-celled parasite has grown to more than 18,000 suspected and confirmed cases in late July, the nation’s largest on record.

The midwest has been hit particularly hard in the outbreak, where public health officials have linked infections in nine states to iceberg lettuce from Taylor Farms’ Mexico operations. The Centers for Disease Control and Prevention (CDC) said people in at least nine states appeared to have connected cases.

“I’m feeling confident we’re heading in that direction, but we need to continue to monitor this as we go forward,” said John Osiecki, vice-president of medical affairs at bioMerieux, the French maker of a panel that tests for 22 gastrointestinal illnesses.

That confidence comes with one big caveat – bioMerieux’s data, published as Syndromic Trends , shows a decline in total test positivity, but heightened public awareness has led more people to take the tests. If a large number of people take the tests and have negative results, positivity rates could be pushed down even as the outbreak continues.

However, Osiecki is hopeful the drop is real, driven by the same public awareness. “I’ve been in a lot of social settings, and I’ve heard people request not to have lettuce just because they’re aware of cyclospora,” said Osiecki.

By contrast, CDC data takes longer, but is published with a high degree of certainty. The CDC has confirmed 6,707 cases of cyclosporiasis acquired in the US and is waiting on data, including interviews, to confirm 11,500 more cases.

Data from the test-maker showed illness involving “parasites” peaked in mid-July, with a 15.6% positivity rate. Cyclosporiasis is known to increase in summer months, but this peak is an outlier compared with the past two years. The same week in 2025 had a parasite positivity rate of 2.9%.

There are a few more caveats about bioMerieux’s data: the panel tests for four parasites, not just cyclospora; Medicare, one of the nation’s largest insurers, only covers the panel for people who are immunosuppressed (the test costs $417 ); and the tests are more likely to be available in population centers than in rural areas.

Whether or not the outbreak is slowing, some food safety researchers have warned it may be larger than currently known. The Food and Drug Administration (FDA) is investigating several outbreaks, which do not yet have a known cause, and the lettuce was sold in 27 states.

In New Hampshire, not currently considered part of the outbreak, the state’s department of health identified cases of people sickened by Taylor Farms lettuce from Mexico as recently as mid-July, linked to a hospital cafeteria in Keene .