As case numbers for cyclosporiasis put an intense spotlight on foodborne pathogens and food safety practices, journalists gathered for a SciLine media briefing titled, “Cyclospora: food contamination, detection and outbreak response.” The webinar featured Kalmia Kniel, a professor of microbial food safety at the University of Delaware, and Craig Hedberg, an epidemiologist and professor at the University of Minnesota. Together, they outlined why cyclospora presents such a persistent threat to fresh produce, how complex distribution networks hinder trace-back investigations and what investments are urgently needed across public health systems.
A Parasite Apart: How Cyclospora Differs From Bacterial Threats
To understand why cyclospora outbreaks are difficult to contain, public health officials look at the biology of the organism. Kniel explains that unlike common bacterial pathogens such as salmonella or E. coli, cyclospora is a single-celled protozoan parasite.
“Cyclospora is really unique,” she says. “We have to remember that it is a single-celled protozoan parasite. It’s not a bacterium, so cyclospora is really different in terms of all biology from salmonella or E. coli. It cannot multiply in the food, and it requires a human host to be able to multiply.”
Kniel says cyclospora is only shed by humans through feces. Furthermore, its transmission dynamics present distinct timing hurdles because it is not immediately infectious upon excretion.
“You may have been hearing in the news that we need this time for the oocysts to become mature,” Kniel says. “That’s when they become infectious, and that’s anywhere from seven to 14 days. The timing involved with cyclospora in terms of its potential to cause contamination is really unique that way.”
The Trace-Back Puzzle: Complex Supply Chains and Lab Limitations
Investigating cyclospora outbreaks poses significant logistical and scientific obstacles. Kniel says fresh produce distribution involves comingling products from multiple farms at centralized distribution centers before shipping them to retailers, which complicates trace back.
Additionally, Hedberg points out that the extended timeline of the disease creates inherent delays for epidemiologists.
“People are being exposed — they get sick as much as two weeks after the food item that they ate that was contaminated,” Hedberg says. “It may be another two weeks before the public health officials learn about that, so we’re always starting quite behind the game in terms of collecting the information and then assembling that and looking for patterns.”
Laboratory limitations further compound the delay. Hedberg explains that unlike bacterial pathogens that can undergo whole genome sequencing to link cases, cyclospora cannot be grown in culture, making genetic extraction difficult.
“Unfortunately, with cyclospora, as we’re investigating these outbreaks in real-time, we just [don’t have the ability] to say that this group of five cyclospora cases are all related and they’re different from this group of 10 cyclospora cases,” Hedberg says. “We’re doing that just based on differences in the time frame, the geographic distribution and some of the exposures that people are relating to us.”
On-Farm Interventions and Consumer Perspective
Addressing contamination requires specific preventative measures at both the agricultural and home levels, such as:
- Water filtration on farms —Kniel explains that water is a primary vector for spreading contamination. Because cyclospora oocysts are relatively large (about 8 to 10 microns), she says filtration serves as a key mitigation step for produce growers using questionable water sources.
- Soil persistence — Kniel cites research showing that parasites related to cyclospora can survive in soil for six months to a year or more.
- Consumer guidance — Kniel says heat treatment is the best risk-reduction strategy for consumers. “Cooking will kill this organism, will kill cyclospora,” she says. She also recommends practicing good hygiene in the home, such as handwashing and cleaning cutting boards to prevent cross-contamination.
- Reassuring the public — Both experts urge the public not to abandon fresh fruits and vegetables out of fear. Hedberg says “the vast majority of food moving through our system, of produce moving through our markets, is not part of this outbreak” and warns that overreaction risks driving people away from a healthy, balanced diet.
The Path Forward: Investing in Infrastructure and Workforce
To improve future outbreak response, both panelists call for sustained investment in public health infrastructure and global supply chains. Hedberg highlights the strain caused by budget cuts at the state and federal levels.
“The workforce that we have available to us is frequently a limiting factor in this,” he says. “We need investments in our laboratory systems and in our people who are working on the front lines of public health to really be more effective at surveillance and control of these outbreaks.”
Kniel says funding is needed in scientific research, training and water treatment systems. Furthermore, Hedberg says that because the food system is global, domestic safety relies on international support.
“The investment in safe water and sanitary sewage disposal that we want to make here, it’s important that we support those in the countries outside of our United States that are also producing food for us. What happens in Mexico or Guatemala matters to us here.”
Expert Q&A: Key Media Questions Answered
Has the Centers for Disease Control and Prevention’s decision to scale back its FoodNet program affected public health officials’ ability to detect or investigate cyclospora outbreaks?
Hedberg: “FoodNet was an active surveillance system developed by CDC that is tracking the occurrence, ... set up to give us a long-term tracking system, not an outbreak investigation system. CDC, because of reductions in some of the resources available to them, made a decision within FoodNet to scale back the number of pathogens that they’re going to continue to track long-term, ... but it hasn’t really had any effect on our ability to identify or investigate outbreaks of any type.”
When case counts jump by hundreds or thousands during an investigation, does that mean the outbreak is actively spreading at that moment?
Hedberg: “When we keep getting reports of thousands of new cases being reported every day, the thing that’s not really clear at all is whether those are really new infections or whether those were people who got sick several weeks ago and just now are getting test results processed and reported into the system. And making those distinctions has a big impact on how we view whether this is really an ongoing outbreak or whether we’re just filling in the gaps in the cases being reported.”
Conflicting statements emerged regarding testing on specific lettuce products. How do false-positive lab tests happen, and does a false positive derail an investigation?
Kniel: “There was a product that was tested. The test was a false positive, meaning that it was either misinterpreted or the testing is actually pretty tricky in itself, ... but that doesn’t change the outbreak. I think that is something that we really want to make sure is clear: that there was still looking at the epidemiological evidence, looking at the signals that were associated with what people were eating.”
Is the agricultural application of septic waste or human sewage responsible for contaminating fresh produce fields?
Kniel: “There is something called the produce safety rule that doesn’t allow for human manure or Class II biosolids to be spread where raw agricultural commodities are grown, so we’re not seeing that typically used for growing fresh produce in the United States. ... It’s almost always really well treated and treated by a specific means that is dictated by EPA, and so it’s not going to have any pathogen growth in there.”
Should consumers avoid produce like raspberries or blackberries because they were linked to cyclospora outbreaks decades ago?
Kniel: “We saw raspberries contaminated in the 1990s, and they’re still on that list of foods, but we haven’t seen any issues associated with cyclospora since then. The industry is working really hard to produce them in a safe manner, and I don’t see any reason to avoid them during this outbreak.”
Hedberg: “Until we identify a food item and say, ‘This is the pathway that this food item was contaminated,’ ... I would not assume that, because berries have been previously associated with other outbreaks of cyclospora, there’s any concern about berries, today.”
