This article originally appeared on the Bloomberg School of Public Health website.
An outbreak of an intestinal illness believed to be tied to leafy greens has sickened thousands of people across the United States this summer, causing symptoms that can persist for weeks—including explosive diarrhea.
Called cyclosporiasis, the illness is caused by a parasite found in contaminated food or water. Once consumed, the parasite reproduces in the digestive tract; when it reenters the environment in feces, it matures to its infectious form in about a week. If it then gets into irrigation water, it can contaminate more crops and infect more people.
While cyclosporiasis cases are more common in the U.S. in summer—the parasite needs warm temperatures to mature—the numbers are low and rarely make headlines. But from May 1 to July 14, the U.S. has confirmed more than 1,600 cases of cyclosporiasis with thousands more suspected—compared to 249 cases at this same time last year, according to the U.S. Centers for Disease Control and Prevention.
How did this outbreak travel so far, so fast? Reasons both regulatory and biological have made it particularly hard to track the source and contain its spread—revealing gaps in America's food safety systems that leave the country more vulnerable to foodborne illness, says Kellogg J. Schwab, a professor in the Department of Environmental Health and Engineering at Johns Hopkins University.
What is cyclosporiasis?
The gastrointestinal illness is caused by a microscopic single-celled parasite Cyclospora cayetanensis. Symptoms arise one to two weeks after a person consumes contaminated food or water.
It is not spread person-to-person. People living in the same household won't get sick from one another but from eating the same contaminated food.
While symptoms can last for weeks, most patients make a full recovery. However, some may require treatment with antibiotics, and dehydration caused by severe diarrhea can be particularly dangerous to people who are immunocompromised.
How does cyclosporiasis spread?
Outbreaks typically begin with contaminated irrigation water that makes contact with fresh produce that ends up on store shelves and on plates.
When it comes to foodborne illnesses, cyclosporiasis "is not the major player by any stretch," says Schwab, but once it has entered the industrial food system, it's hard to contain. Unlike bacteria such as E. coli, salmonella, and listeria—the pathogens most commonly associated with food recalls—Cyclospora is a parasite, and it behaves differently in almost every way that matters for containing an outbreak:
It can survive in soil and water for weeks or months and still cause illness. Once an infected person passes the parasite through defecation, it takes one to two weeks after reentering the environment for it to then mature enough to become infectious to someone else. That delay obscures the connection between cases.
It evades standard food sanitizing treatments. Products like chlorine that industrial food processing plants normally rely on to disinfect products have essentially no effect on Cyclospora. The only reliable way to kill the parasite—with heat at temperatures around 160°F—isn't a practical option for salad greens, raspberries, herbs, and other fresh produce that is often the source of Cyclospora outbreaks.
Cyclospora is difficult to study and detect. Unlike many bacteria, it doesn't grow in laboratory culture, and state labs often lack the specialized tools to identify it quickly, further slowing the response.
That combination of hardiness, a long incubation period, and resistance to conventional disinfection means the best safeguard against Cyclospora is to keep it out of the food supply at the source.
What about food safety regulations?
The erosion of food safety staff, funding, and surveillance have reduced opportunities to identify the outbreak's source and stop its spread, says Dave Love, a research professor at the Center for a Livable Future.
The U.S. has long relied on an approach called Hazard Analysis Critical Control Points, or HACCP, originally developed in the late 1950s by NASA and Pillsbury to keep astronauts from getting food poisoning in zero gravity. HACCP maps out every point "from farm to fork, those key choke points" where contamination could occur, and builds in monitoring and a "stop" mechanism when something goes wrong, Schwab says. It works—but only when it's actively maintained, reported, and enforced.
According to Schwab, the enforcement piece is what has eroded. Federal agencies have lost staff and funding needed to inspect, audit, and monitor food producers, leaving more of the system dependent on voluntary industry self-regulation.
"Self-regulation works until it doesn't," Schwab says. That's where FoodNet came in. FoodNet is the joint CDC-FDA-USDA-EPA active surveillance system that tracks foodborne illness across 10 sentinel sites. Cyclospora reporting was mandatory until July 2025 when the Trump administration made reporting optional for Cyclospora, along with five other pathogens (Campylobacter, Listeria, Shigella, Vibrio, and Yersinia).
"Cuts to food safety ... make the food system more susceptible to these types of outbreaks," says Love.
Why did cyclosporiasis spread so far?
In a well-functioning system, Schwab says, an early cluster of cases in one state gets reported to the CDC, which can quickly check whether other states are seeing the same pathogen in the same food product and flag it as a multistate event. "The quicker you do that, the lower the burden on the entire population," he says.
That coordination function has been degraded. With reporting voluntary and federal staff reduced at agencies like FDA, the connections between state and federal surveillance have frayed. Without a coordinated national surveillance system, what remains is a patchwork of state-led efforts: Maryland, California, New York, and Minnesota, for example, have kept up more robust food monitoring programs, while states like Alabama and South Carolina have far less capacity to do so.
The country's industrialized food supply chain exacerbates the consequences of those gaps. Produce from many small farms is routed to centralized processing plants and then mixed, bagged, and shipped nationwide. Once it's in the system, a single contamination event doesn't stay local, says Love. "It's an efficient way to produce lettuce at a large scale. It's also a very efficient way to spread disease."
How can future foodborne outbreaks be avoided?
Restoring surveillance capacity, Schwab argues, is the central fix: a fully funded, fully staffed federal system with mandatory pathogen reporting so that multistate patterns are identified within days rather than after an outbreak has already spread nationwide. States that have kept investing in their own monitoring show what's possible, but a state-by-state patchwork can't substitute for a coordinated federal response, particularly for products that cross state lines.
It's critical to ensure that there are strict controls on irrigation water, and on-farm sanitation practices can minimize risks, says Love: "Are farm workers given time to go to the bathroom? Are bathrooms provided to them? Do they have a handwashing station with warm water? That gets back to, you know, how do you treat your workers?"
While no amount of individual caution can substitute for a functioning regulatory system, consumers can minimize their risk by cooking food thoroughly, choosing lower-risk produce if they're immunocompromised, and "washing your hands," Schwab says. "It's the single most important thing we do in public health."
"This is a very large outbreak because we didn't stop it in time." Cyclospora is a hardy and tough-to-track parasite. With a food-safety system stripped of the staff, funding, and reporting requirements needed to catch contamination before it spreads nationwide, an outbreak like this "was inevitable. We knew this was going to happen."
Yet that doesn't have to be the end of the story, Love says. "These foodborne outbreaks are going to happen year after year. It's really how you deal with it. That's the story."
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