A major US cyclosporiasis outbreak has reached over 18,000 cases, with test-makers observing a potential decline in positivity rates amid heightened public awareness.

The US is experiencing its largest recorded outbreak of cyclosporiasis, a gastrointestinal infection caused by a single-celled parasite. While more than 18,000 suspected and confirmed cases have been reported as of late July, a major diagnostic test manufacturer suggests the outbreak may be slowing. Public health officials have linked infections across nine states to iceberg lettuce sourced from Taylor Farms’ operations in Mexico.

Testing Data and Trends

Data from bioMerieux, which produces a diagnostic panel for gastrointestinal illnesses, indicates that parasite positivity rates peaked in mid-July at 15.6%. This figure represents a significant increase compared to the 2.9% positivity rate recorded during the same week in 2025. John Osiecki, vice-president of medical affairs at bioMerieux, noted that while the data suggests a decline, the results must be interpreted with caution due to increased public awareness and testing volume. Additional factors complicate the data, as the bioMerieux panel tests for four different parasites rather than just cyclospora. Furthermore, the test is primarily covered by Medicare for immunosuppressed patients and is more readily available in urban centers than in rural areas.

Official Case Counts and Investigations

The Centers for Disease Control and Prevention (CDC) has confirmed 6,707 cases of domestically acquired cyclosporiasis and is currently processing data for an additional 11,500 suspected cases. The Food and Drug Administration (FDA) is also investigating several other outbreaks that currently lack a confirmed cause. Reports indicate that the implicated lettuce was distributed across 27 states, and health officials in New Hampshire recently identified cases linked to the product in a Keene hospital cafeteria.