Officials monitoring a cyclosporiasis outbreak that has grown to more than 18,000 suspected and confirmed cases are cautiously optimistic about signs of deceleration. The outbreak, attributed to contaminated iceberg lettuce from Taylor Farms’ Mexico operations, has been particularly severe in the Midwest, with confirmed connections in nine states.
BioMerieux, a French manufacturer of gastrointestinal testing panels, reported declining test positivity rates in data released as Syndromic Trends, suggesting potential slowdown. The company’s laboratory data showed parasite-related illness peaked in mid-July with a 15.6% positivity rate, compared to 2.9% during the same period in 2025. John Osiecki, vice-president of medical affairs at bioMerieux, expressed cautious optimism about the direction of the outbreak, attributing potential improvement partly to increased public awareness that has discouraged consumption of lettuce.
However, analysts noted significant limitations in interpreting the test-maker’s data. While heightened awareness has driven more people to seek testing, increased testing volume with negative results could artificially suppress positivity rates even if infections continue. Additionally, the panel tests for four different parasites rather than cyclosporiasis alone, and coverage limitations restrict access for certain populations. Meanwhile, CDC data, which carries greater certainty, shows 6,707 confirmed cases with approximately 11,500 additional cases awaiting confirmation through interviews and investigation.
Experts have raised concerns that the outbreak may be larger than currently documented. The FDA is investigating multiple gastrointestinal illness outbreaks with unknown causes, and the contaminated lettuce reached 27 states. Recent cases identified in New Hampshire, including illnesses linked to Taylor Farms lettuce in a hospital cafeteria in Keene as recently as mid-July, demonstrate geographic spread beyond the nine states initially implicated in the outbreak.
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