America’s Homegrown-Parasite Problem
Scientists don’t know why cyclosporiasis, a tropical diarrheal disease, is spreading more and more from domestic sources.
The other night, I found myself in the unenviable position of trying to cook a salad. And I mean cook a salad: I spread fresh, delicious-looking gem lettuce in a pan and watched it wilt away into a sad, heated blob. America appears to be in the midst of an outbreak of—I’m sorry, but there’s no better way to say this—explosive diarrhea. More than 2,900 people nationwide have reportedly been sickened by the parasite Cyclospora cayetanensis, which has historically been spread through raw produce, including basil, cilantro, raspberries, and, yes, lettuce. The resulting illness, cyclosporiasis, causes bouts of diarrhea that, if left untreated, can wreak havoc on the digestive system for a month.
Cyclospora is most common in tropical climates and areas with substandard sanitation. It’s spread through contact with bits of human waste that have sat in a warm environment for a week or two, allowing the parasite to mature and become infectious. One of the first documented large-scale outbreaks of foodborne cyclosporiasis in the United States, for example, was caused by raspberries imported from Guatemala. In recent years, though, it’s started to seem that the U.S. has a homegrown-parasite problem on its hands. Americans were sickened in both 2018 and 2020 by outbreaks that were believed to be caused by domestic produce. The FDA set up a task force to deal with the issue in 2019. It apparently hasn’t stopped what is looking like a dramatic uptick in cases this summer. Michigan usually sees about 50 cyclosporiasis cases a year. During this current outbreak, it has recorded upwards of 1,500.
Officials and scientists are not yet sure just how dire the apparent rise in cyclosporiasis is and whether the cases around the country are actually connected. Although the CDC reports that 31 states are seeing cases, the majority are reporting fewer than 10, which is close to normal for the summer months.
They also don’t know what is behind this spate of illness. Don Schaffner, a food scientist at Rutgers University, told me his theory is that perhaps the largest cluster of cases came from people swimming in or otherwise consuming water from a common water source, such as Lake Erie, which borders the affected states of Michigan and Ohio. Michigan’s chief medical executive has said, however, that the state’s working theory is that the cases are tied to produce.
That lack of clarity has led public-health officials to offer somewhat unsatisfactory advice on how to keep yourself safe. My home state of Illinois suggests that people avoid food and water “that may have been contaminated with feces,” as if that were not always the goal. Other states recommend washing produce, but that won’t eliminate all of the risk, Schaffner said. Some experts believe that washing might help reduce the number of infectious particles that a person takes in, but they don’t know for sure how many a person needs to ingest to actually get sick, and some data suggest that the number may be very low. The only way to reliably kill the parasite is to cook your food thoroughly—hence my feast of wilted, warm greens.
Americans have little other recourse to protect themselves from cyclosporiasis and, thanks to ongoing uncertainty about the outbreak’s size, little way of knowing how likely they are to catch it. In healthy people, cyclosporiasis causes mostly mild (if uncomfortable) symptoms. But that lack of control still makes cyclosporiasis, like other foodborne illnesses, unsettling and frustrating. Right now, choosing to eat only cooked produce is one of the few decisions I can make to protect my fast-approaching wedding from being interrupted by frantic trips to the bathroom, so I’m going with it.
When a foodborne outbreak happens, public-health officials’ goal is to quickly identify its cause and warn people to stay away from the suspect food. Sometimes that happens quickly—in 2018, for example, investigators took just nine days to tie an E. coli outbreak to chopped romaine. The current investigation into cyclospora has already been happening for nearly a month. In the coming weeks, Americans might learn the cause, or causes, of the surge, which would make taking precautions much easier. And if the parasite has been in fact spread by raw produce, the contaminated products may already be off grocery-store shelves.
Cyclosporiasis, though, is particularly tough to track. Scientists can analyze the genetic sequence of most pathogens to identify clusters of related diseases, but that process doesn’t work as well for cyclospora, because the parasite is difficult to extract from stool and can’t be grown in a laboratory for testing the same way other pathogens can. And even if officials zero in on specific foods that they believe were contaminated, the public may never learn what specifically went wrong. The CDC’s website notes that “no one fully knows how Cyclospora gets into food and water.” Although past investigations of the parasite have turned up suspected sources, they have stopped short of concluding how those sources became contaminated. When bagged lettuce caused a cyclospora outbreak in 2020, for example, officials suspected that the parasite had been introduced to farms through a municipal water canal, but they were ultimately unable to definitively establish a causal link. The investigation may also be hindered by the Trump administration’s recent cuts to the CDC and the FDA. Until yesterday morning, the CDC was reporting that fewer than 200 people in the U.S. had contracted the parasite, despite ample evidence from states that the situation was much more severe. It has since updated that count to 843. (A CDC spokesperson declined to explain the earlier discrepancy between state reporting and its own case count, and did not respond to a follow-up request for comment after the new numbers were released.)
Cyclosporiasis, thankfully, is not the most serious foodborne illness that the world has to deal with. Although cyclosporiasis has landed nearly 100 Americans in the hospital so far this summer, no one has died. That’s much preferable to, say, the 2024 listeria outbreak tied to lunch meat that killed 10 people. In that case, a clear culprit was identified, and there were consequences for the company that produced the tainted meat, which has paid out millions in settlements. The United States may never get the same closure to its cyclospora problem.