On July 10th, a friend sent me a text message that spoke for an anxious nation. “What if I have the explosive-diarrhea disease?” she asked. She included a link to an article about a parasitic illness, called cyclosporiasis, that was spreading across multiple states, mostly clustered around the Great Lakes region. The outbreak in Michigan, which was the most afflicted state by far, had begun in May and was up to nearly a thousand cases (compared with fifty in a typical year). Confusingly, the Centers for Disease Control and Prevention’s nationwide tally of confirmed cases was just a hundred and forty-five—an order of magnitude less than the number reported in Michigan alone.

Within an hour of receiving my friend’s text, I had forty-eight cyclosporiasis-related tabs open on my laptop. Cyclospora, I learned, is a protozoan parasite found in produce that has been tainted with human feces—perhaps because heavy rains flooded the porta-potties on the farm where the produce was grown, or because it was irrigated or washed with contaminated water. The cyclospora parasite travels inside an oocyst, a sturdy pod that can find purchase in the nooks and crannies of berries or cling to the ridges and folds of certain greens—and it will die there only if cooked. Once these oocysts reach the human digestive tract, the outer coating dissolves and the parasite unleashes a Visigoth invasion of the small intestine, causing nausea, cramping, and what has been described as “watery diarrhea,” “relentless diarrhea,” and, most vividly, “explosive diarrhea.”