As cases of explosive diarrhea continue to rise across the US this summer, health officials are grappling with a longstanding question about the tiny parasite that’s behind all this torment: Just how the heck is poop getting into our food? The appalling truth about cyclospora is that humans are its lone source. It’s only ever been found in human feces. So if it’s in our food or water, “it doesn’t take a rocket scientist or a microbiologist to overthink this,” said Dr. Mark Moorman, who recently retired as director of the Office of Food Safety at the US Food and Drug Administration. “Humans are the source.” And here’s another unsettling thing about cyclospora: Investigators have never definitively identified the cause of an outbreak. In several cases, they’ve found some strong suggestive evidence that puts cyclospora close to produce growing or processing, but they’ve never identified how the poop is entering the agricultural system in the first place. That question is becoming more pressing, however, as the US contends with its largest ever cyclospora caseload, which has swelled to more than 11,500 confirmed and suspected cases across 41 states, according to the CDC. These are cases that were acquired in the US, rather than from travel abroad, which makes this year unusual. “Typically, we only see 2,000 to 4,000 a year, so this is a pretty big spike,” said Dr. Keith Schneider, a professor of food safety at the University of Florida. Generally, about 1 in 5 is acquired during international travel. Cases of cyclospora tend to rise during the summer months. This year, the FDA has launched investigations into six outbreaks. The largest of these is a nine-state outbreak in the Midwest believed to be linked to iceberg lettuce grown in Mexico. The FDA recently announced that it is looking into another cluster of 72 related cases that doesn’t yet have a known source. “We’ve not seen anything like this,” said Dr. Kali Kniel, a professor of microbial food safety at the University of Delaware. Typically, the US might investigate one or two outbreaks of cyclosporiasis each year. “I think we’re looking at an unusual year with multiple outbreaks happening at the same time.” The search for a ‘smoking gun’ Many times, these investigations close without – shall we say – solid leads. “We just don’t have much in the way of success stories to say, ‘Ah, got it, smoking gun,’ ” Moorman said. In 2013, for example, an FDA investigation into a cyclosporiasis outbreak linked to salad mix processed by Taylor Farms de Mexico failed to find the parasite in its testing but noted that the medical records of harvesting workers showed that they had taken antidiarrheal medications or the combination antibiotics that are used to treat cyclosporiasis. Those medications can be used for other reasons too, however, and no diagnoses were recorded in the records that were inspected by the FDA. Cyclospora outbreaks are difficult to investigate in large part because of the parasite itself. People who ingest tainted food or water don’t get sick right away. It can take up to two weeks for the cramping, nausea, watery diarrhea and bloating to start. By the time people realize that their symptoms aren’t going away and seek medical attention, it may be three weeks to a month after exposure. Lab testing a stool sample to confirm the illness also takes time. Then, the case has to be reported to a local health department, which has to call the person to interview them about what they might have been exposed to. Most people are notoriously bad at recalling what they ate for breakfast, let alone what they may have eaten a month ago, so contact tracers often pull in electronic records from shopper cards and bank statements to help fill in the picture. All that data must then be analyzed to look for a common exposure. This summer, iceberg lettuce stood out as the most likely suspect in the largest outbreak, but several other clusters still don’t have a suspected source. Most of this work is done by state health departments, and in the case of a multistate outbreak like this one, state health departments working in conjunction with the US Centers for Disease Control and Prevention. After the CDC feels confident that its data points to a source, agency experts turn the investigation over to the FDA. The FDA then traces the food back to a supplier and ultimately to the farms that grew it. A team will do an environmental assessment, where the investigators walk a farm and take thousands of samples of soil, water and produce for testing. By the time FDA inspectors actually make it to a farm, however, the outbreak is usually over. “All of that time is really tricky,” said Dr. Kali Kniel, a professor of microbial food safety at the University of Delaware. “By the time you do that, these products with shelf lives are gone, and they’re not being grown or harvested anywhere,” said Kniel, who teaches a class in outbreak investigation. ‘Water is number one’ It’s rare for lab tests to ever find cyclospora parasites in the environment. But they did in 2020, during an investigation into Fresh Express bagged salad kits that were linked to more than 700 cyclosporiasis cases across 14 states that summer. Many food safety experts feel that these detections were the nearest anyone has come to pinpointing the source of an outbreak. “It’s about the closest that I’m aware of, where we had a clue, and it’s where in canal water we pulled up the cyclospora pathogen,” said Moorman, who oversaw the investigation for the FDA. The Fresh Express salad kits contained iceberg lettuce, carrots and red cabbage, leading to investigations into multiple farms that grew the vegetables. Eventually, the FDA conducted a full environmental assessment at a farm in Florida that grew red cabbage for the mix. The agency’s testing identified cyclospora in two samples taken from a canal that the farm used for irrigation. But lab testing for cyclospora is complex, as the FDA acknowledged in a warning letter to Fresh Express. “Given the emerging nature of genetic typing methodologies for this parasite, the FDA has been unable to determine conclusively if the Cyclospora detected in the canal is the cause of this outbreak,” agency staff wrote. “However, water and soil contaminated with fecal matter may act as a vehicle of transmission for C. cayetanensis infection,” the FDA said. Fresh Express did not respond to CNN’s request for comment on the FDA’s testing. Even with the test results, Moorman said, they were never able to figure out how feces might have been getting into the canal in the first place. Most experts believe that water contaminated with cyclospora is the vehicle that puts the parasite on produce. “Water is number one,” said Dr. Jennifer McEntire, a microbiologist who consults with food companies on their safety practices. “Now, how that water gets contaminated with human fecal material is another question.” It’s not likely that anyone is using the bathroom directly into irrigation water, McEntire says, but unintentional contamination of water could be a factor. Most farms supply portable toilets or bathroom trailers to workers in the fields. Could waste emptied from those have ended up in the canal? Did a septic tank in the area leak or break, allowing waste to seep in? Did heavy rainfall cause a sewer system to overflow? McEntire said it’s possible that sick workers might spread the parasite as they handle food, but she thinks that’s less likely. It’s difficult for her to imagine that one sick person or even a harvest crew could contaminate so much produce that it would make this many people ill, she said. “But that’s the other route, a slightly more direct route, going back to the people themselves versus the water.” Moorman felt like it was enough evidence to urge the members of the Florida Fruit & Vegetable Association to do more testing of irrigation water and produce during the growing season. But that’s all he could do. There’s no law or rule that requires farms to test irrigation water or produce for cyclospora, Moorman said. “It’s voluntary,” he said. With few exceptions, “we don’t have those levers at the FDA.” Big companies that purchase produce, such as Kroger, Food Lion or Costco, could require their suppliers to test for it, he said, and that might help prevent outbreaks. The government could also pass laws to require testing for cyclospora and could allocate more funding to research this parasite and the infection it causes. For her part, Kniel, at the University of Delaware, says she’s just glad that people are finally paying attention. “I’ve actually asked every year when there are 2,000 cases of this, ‘Why does no one care? Why are we not talking about it?’”
