In November 2013, after Cyclospora cayetanensis sickened hundreds of people in Iowa and Nebraska, FDA published an environmental assessment of the Taylor Farms de México processing plant at Doctor Mora, Guanajuato. The report closed with recommendations. The second told the firm to determine whether Cyclospora is a reasonably likely hazard in the Guanajuato leafy green growing region and, if it is, to re-evaluate the wash step used on salad mix. Thirteen years later the same region sits at the center of the largest cyclosporiasis outbreak in American history, and no one has produced a document showing that determination was ever made.

Here is what a hazard analysis would have found, had anyone performed one. Two hundred and thirty-five meters from the processing building — roughly eight hundred feet, a three-minute walk — sits Balneario Las Fajanas, a public thermal-water bathing complex with pools, water slides, changing rooms, showers, grills and picnic shelters, open every day of the year. It is the largest concentration of human fecal loading anywhere near that plant. And satellite imagery establishes that it was already built, filled and operating in March 2010, more than three years before FDA and COFEPRIS ever set foot on the property.

That image forecloses the only innocent explanation. Nobody can now say the balneario came later, or that the environment changed after the inspectors left. When FDA and COFEPRIS walked that site in August 2013, a public bathing facility with filled pools stood across the highway in plain view and had stood there for years. The published assessment describes the processing plant and five ranches. It does not describe a bathing complex.

It is worth setting out what is actually on that property, because the detail matters. The Guanajuato Secretariat of Tourism lists Las Fajanas in its official state guide under balnearios and water parks, at Km 16 of the San Miguel de Allende–Doctor Mora highway, locality of Cruz de la Maza, with state-published coordinates of 21.10266, -100.45159. The state describes thermal-water pools, extensive lawns, parking, water slides, palapas, grills, restrooms, showers, changing rooms and a snack shop, and flags the site as accessible. Other listings add a soda fountain, a store, sports courts and a bar. The operator advertises thermal water held at 40 degrees Celsius and promotes that the facility is open 365 days a year. Admission has climbed steadily — 80 pesos for adults and 40 for children in earlier listings, 100 and 40 after that, 120 and 60 from the first of February, and 150 adults and 80 children from the twenty-third of March. Prices rise like that when demand supports it. The Google listing carries 897 reviews. There is no website; the business runs on Facebook.

Water slides produce high water ingestion, particularly among children. Grills and picnic shelters mean families stay all day rather than an hour, which multiplies restroom use per visitor. Thermal water at 40 degrees means the facility is drawing from a deep geothermal source and moving large volumes of it — and every liter that goes into a pool eventually comes out of one. Where it goes when it leaves is the entire question, and no public listing answers it.

Put the two frames side by side and a second argument appears, one that has nothing to do with the balneario. The bathing complex in 2023 looks much as it did in 2010. The Taylor Farms facility does not. The 2010 image shows a moderate plant: one main building, blue-roofed outbuildings, a large unpaved graded area to the north. The 2023 image shows a substantially larger processing building, a solar array along the western boundary, hundreds of employee vehicles in formal parking rows, and a trailer yard holding well over a hundred units. That is not incremental growth. That is a different scale of operation — more throughput, more wash water, more workers, more waste.

One more feature is visible in both frames and deserves attention from someone qualified to identify it. A linear channel runs east to west immediately north of the highway, between the plant and the balneario, and appears to hold water in both images. The 2023 frame also shows a standing water body along that channel southwest of the plant. If that is an irrigation canal or a drainage ditch, it is a surface pathway between the two properties — and surface connection is far easier to establish than aquifer connection. It would also have been visible from the plant yard in 2013. Separately, the 2010 frame shows a dark oval pond immediately southwest of the main building that I cannot find in the 2023 frame. If that was a retention or process-water lagoon, its disappearance during the expansion is a records question worth asking.

Cyclospora cayetanensis has no animal reservoir. Cattle do not carry it, wildlife does not carry it, birds do not carry it. It completes its life cycle in human beings and nowhere else. Every oocyst that ends up on a leaf of iceberg lettuce came out of a person. With E. coli O157:H7 you go looking for a feedlot upgradient of the field. With Cyclospora you go looking for human sewage.

Cyclospora Oocysts are shed unsporulated and non-infectious. They must sit in the environment for roughly one to two weeks at temperatures between about 22 and 32 degrees Celsius before they can infect anyone, which is why CDC says direct person-to-person transmission is unlikely. A sick person cannot hand this parasite to the person beside them. What that person can do is deposit inert oocysts into soil or water, walk away, and leave them to ripen. And northeastern Guanajuato is close to ideal for that ripening: mean daily maximum temperatures at San José Iturbide run from about 23 to 31 degrees Celsius across the entire year, sitting inside the sporulation window in every month.

I want to be careful here, because there is a version of this argument that is wrong. On July 15 the International Fresh Produce Association faulted Michigan’s health department for saying recreational water is not a recognized risk factor, cited three papers for the proposition, and told The Packer that Michigan was defying reputable science. Its consumer FAQ still tells readers that pool chlorine will not kill Cyclospora and that people who swallow pool water are not protected the way they would be from other waterborne illnesses. County health departments in Ohio and Arizona have said much the same thing. The implication running through all of it is that swimmers are catching this. They are not.

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