After weeks of stirring up gastrointestinal issues across the country, especially in the Midwest, the parasite Cyclospora—which lives on fresh produce and causes explosive diarrhea—is steering grocery runs and restaurant orders for many consumers.
Cyclospora is transmitted when human feces contaminate lettuce and other crops during growing or processing stages. With no direct source of infection yet identified in the current spread, many people are wondering when we can once again enjoy summertime leafy greens worry-free
Experts can’t quite agree on an answer.
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As of July 24, in Michigan alone, there were 8,176 reported cases of cyclosporiasis, the gastrointestinal illness caused by Cyclospora, since June 22. Michigan has seen the largest outbreak this summer and is tracking cases most closely. Compared with the 40 to 50 cases the state sees in a typical year, this is unprecedented, says Natasha Bagdasarian, chief medical executive for Michigan. And it’s likely an underestimate. Because of how expensive and resource-hungry testing can be, Bagdasarian believes that these thousands of cases are “just a sample” of the true outbreak.
The Centers for Disease Control and Prevention has tied the outbreak in Michigan to dozens of other cases in eight other states across the Midwest and the South. And the Food and Drug Administration is also investigating contaminations that may be tied to a different outbreak.
According to Gerardo Lopez, who studies the parasite at University of Arizona, the number of cases may taper off soon. Based on Cyclospora’s typical lifespan and contamination cycle, cyclosporiasis infections usually increase in early summer and drop off by August.
“We’re already past mid-July and heading toward the end of it,” Lopez says. “This should be the peak.”
In a statement to Scientific American, the Food and Drug Administration, which is working to trace back the cases to a specific product, also emphasized that cases will likely decline, adding that “it is important to understand that Cyclospora has a defined seasonal pattern.”
Lopez says he’s confident in the FDA’s ability to eventually trace the outbreak despite a lack of identification so far. It’s especially difficult to trace Cyclospora, he says, because the parasite can take up to two weeks to produce spores after contamination and another two weeks to cause symptoms if someone consumes spore-covered produce.
Last week the FDA traced some cases back to lettuce from the company Taylor Farms de Mexico, which recalled all of its iceberg lettuce sourced from Mexico from stores and restaurants before the FDA discovered a test for Cyclospora had provided a false positive. The false positive, Lopez says, doesn’t change the fact that the cases seemingly stemmed from that source and that the affected products have been removed from circulation.
“Things should be returning back to normal,” he says. “The commodity is going to be off the shelves. We’ve never seen any type of outbreak that has continued past that window.”
Bagdasarian, Michigan’s medical executive, isn’t so sure the end is in sight yet. This level of outbreak, she says, “goes way beyond normal seasonality” of the parasite. And she’s worried about the possibility of cross-contamination or machinery contamination that could be bringing the outbreak beyond a single product.
The Michigan Department of Health and Human Services has been intensively tracking the outbreak since early July in a process that’s “atypical” at a state level, Bagdasarian says. Staff from all over the department have left other projects to interview thousands of people diagnosed with cyclosporiasis. The “very tedious work” involves calling people all over the state and convincing them to recall everything they’ve eaten in the past month in a lengthy questionnaire before entering all the data manually for analysis.
Even this, Bagdasarian says, is not enough to really understand and bring an end to this outbreak. She’s calling for stronger and more integrated federal efforts, including confirmation of which specific products contain Cyclospora from the FDA and a unified tracking database from the CDC.
“We really need to understand how our data compares to what’s happening in Ohio, what’s happening in Indiana, what’s happening in New York,” she says. “There needs to be a coordination of data analyses.”
Nicole Arnold, a food safety researcher at the Ohio State University, says the outbreak affecting Michigan and other states should reach its end soon—but that this doesn’t mean our summer of cyclospora is over. Although the affected lettuce should be close to reaching the end of its shelf life, she says, this accounts for just one of what may be several concurrent outbreaks across different states.
“It is my understanding that multiple cyclosporiasis outbreaks are taking place simultaneously,” she says. “There seems to be progress toward confirming the source of the cyclosporiasis outbreak affecting the Midwest; however, the sources/foods associated with other cyclosporiasis cases are currently unknown.”
In the meantime, experts are recommending a summer diet that avoids bagged salads and removes the outer layer from any fresh produce. And even once the outbreaks come to an end, Bagdasarian says, she hopes they bring public and government awareness to the needs of state public health systems.
“This is not a wake-up call for us; we have been raising the alarm for months and years,” she says. “When there is a public health emergency, when there is a large outbreak, when something big happens, it really tests this very stretched system. I hope that now this is a wake-up call for the American public.”