Cyclosporiasis: Case rates rise in five outbreak states

Data: CDC; Map: Brad Jennings/Axios. Note: Estimated rates calculated using CDC case range midpoints and 2025 U.S. Census population estimates.

Cases of cyclosporiasis have now been reported in at least 41 states, and infection rates continue to increase in the five states where the CDC has declared an outbreak.

The big picture: Although some cases of the diarrhea-inducing illness are reported each year, the outbreak will make 2026 the worst year on U.S. record for this food-borne parasitic infection.

The latest: The CDC this week reported 4,173 confirmed cases in the U.S. between May 1 and July 20. That's already more than the total number of U.S. cases reported for all of 2025.

Investigations continue to center on contaminated iceberg lettuce as a source for the outbreak.

Zoom in: Michigan has by far the highest number of lab-confirmed domestic cases: between 900 and 2,100.

That yields an estimated infection rate of nearly 15 per 100,000 people, using the midpoint of that CDC-reported range and 2025 U.S. Census state population estimates.

Nearby Ohio (3.36 per 10,000 people), Indiana (3.33) and Kentucky (2.61) and West Virginia (1.16) are also named in the outbreak.

Between the lines: Case numbers are likely higher than the map suggests.

The CDC also notes that it's aware of at least 7,400 cases — many from Michigan and Ohio — that have not yet been lab-confirmed.

And some people who get sick never get tested for cyclosporiasis.

Yes, but: Cyclosporiasis cases occur every year, so the presence of singular cases in a given state isn't necessarily alarming.

It's the growing number and concentration of cases this year that have health agencies concerned.

What we're watching: Whether case numbers keep rising in the coming weeks, even as mitigation around potential contaminants continues, because there's a lag between illness onset and reported case.

The bottom line: Case totals will likely get worse before they get better. ...