food-safety · family: it worked in the lab
a parasite onlya lab can find
FDA has a laboratory method for Cyclospora on fresh produce, but industry still has no rapid test kit and the parasite cannot yet be grown
Problem statement
Cyclospora cayetanensis, a protozoan parasite that causes a diarrheal illness which, untreated, typically lasts 10–12 weeks (CDC DPDx), has been recognized since the mid-1990s as the cause of multistate outbreaks in the United States and Canada, mostly linked to fresh produce (Almeria et al. 2019); in the United States, outbreaks have been identified nearly every year since the mid-1990s (CDC DPDx), most of the domestically acquired ones linked to imported fresh produce such as raspberries, basil, cilantro, parsley, lettuce and other leafy greens (FDA Cyclospora action plan), and the parasite is hard to detect on produce surfaces. Unlike bacterial foodborne pathogens (Salmonella, E. coli), Cyclospora has no in vitro culture system and no animal model, so the only biological material available for research is oocysts isolated from patients' stool (Almeria et al. 2019), and recovering its oocysts from produce, which usually carries only low numbers of them, is a key and difficult step in detection (Almeria et al. 2019). Current molecular detection (PCR-based) can have poor sensitivity on produce matrices, so produce that makes people sick can test negative in the laboratory. FDA publishes a recommended laboratory method for fresh produce (Bacteriological Analytical Manual chapter 19b) and says there is still a critical need for test kits that industry can use; it has begun studies on growing the parasite in the laboratory and, with CDC, is building a genotype database for linking cases to foods (FDA Cyclospora action plan).
Why this matters
In 2023, CDC counted 2,272 laboratory-confirmed cases of cyclosporiasis in people who had not travelled outside the United States, with illness onsets from April 1 to August 31, reported by 40 states and New York City; of the 2,242 with information available, 186 were hospitalized (CDC 2023 final update). Without a reliable detection method, it is harder to confirm contamination sources during outbreaks, to conduct surveillance sampling, and to verify the effectiveness of preventive controls. Contaminated shipments may be identified through epidemiological investigation after people get sick, and contaminated produce can continue to enter the food supply during the investigation. Whole genome sequencing is used to detect and solve foodborne outbreaks caused by bacterial pathogens, but FDA is still working to develop the capacity to sequence parasites such as Cyclospora cayetanensis. In July 2026 CDC said that whole genome sequencing is not currently available to match a contaminated product to a Cyclospora outbreak strain; federal partners use targeted genotyping instead, which is not as fast or precise, so cyclosporiasis investigations generally take longer to link cases to each other and to a source, and in some cases a source is never identified (CDC media briefing, July 14, 2026).
What’s been tried and why it hasn’t worked
PCR-based methods (FDA BAM Chapter 19b) can detect Cyclospora DNA, but in berries such as raspberries and strawberries PCR analysis is challenging because of many inhibitory substances and the low concentration of parasites, qPCR inhibition has also been seen with cilantro (Bartosova et al. 2021), and recovering oocysts from produce is difficult because naturally contaminated produce usually carries low numbers of them and methods for clinical samples do not always transfer to produce (Almeria et al. 2019). Isolating and concentrating oocysts with antibody-coated beads, as is done for Cryptosporidium parvum, would likely improve efficiency, but antibodies against Cyclospora are not yet commercially available (Almeria et al. 2019). Under the microscope, in stool samples, the small (8–10 µm), round oocysts can be confused with amoebae or inflammatory cells, so alternative microscopic methods are needed for higher sensitivity; strong autofluorescence under UV light is a useful identifying test (Almeria et al. 2019). Microscopy-based identification requires laboratory infrastructure and trained microscopists.
What would unlock progress
Improved oocyst concentration and extraction methods optimized for complex produce matrices — achieving consistent recovery from surfaces where oocysts are physically trapped. High-affinity antibodies or aptamers specific to Cyclospora cayetanensis oocyst surface antigens that could enable immunocapture-based concentration and detection. Metagenomics approaches that can detect and genotype Cyclospora directly from produce wash water without culture enrichment. A complete reference genome and genomic epidemiology framework comparable to those available for bacterial foodborne pathogens.
Entry points for student teams
A student team could systematically compare oocyst recovery rates across different produce extraction methods (stomacher, pulsifier, sonication, enzyme-assisted) using spiked samples on representative produce matrices (berries, herbs, leafy greens), identifying which matrix-method combinations achieve acceptable recovery for downstream PCR. Alternatively, teams could develop an aptamer-based detection approach for Cyclospora oocyst surface antigens using SELEX with commercially available oocyst preparations. Relevant disciplines: food science, microbiology, analytical chemistry, molecular biology.
Genes
Structural cousins: stuck the same way, in other fields
Sources
National Academies of Sciences, Engineering, and Medicine, "The Food Forum 30th Anniversary: Proceedings of a Symposium," 2024, "Accelerating the Use of Pathogen Genomics and Metagenomics in Public Health," 2025, Food Forum, Food and Nutrition Board; accessed 2026-02-20; U.S. Food and Drug Administration, "Cyclospora Prevention, Response and Research Action Plan," page dated 09/11/2026, accessed 2026-09-29; Almeria S, Cinar HN, Dubey JP, "Cyclospora cayetanensis and Cyclosporiasis: An Update," Microorganisms, 7(9):317, 2019, (read at ), accessed 2026-09-29; Bartosova B, Koudela B, Slana I, "Detection of Cyclospora cayetanensis, Echinococcus multilocularis, Toxocara spp. and microsporidia in fresh produce using molecular methods: – A review," Food and Waterborne Parasitology, 23:e00124, 2021, (read at ), accessed 2026-09-29; Centers for Disease Control and Prevention, "DPDx – Cyclosporiasis," accessed 2026-09-29; Centers for Disease Control and Prevention, "Cyclosporiasis Illnesses in the United States, 2023" (last and final update October 26, 2023), Internet Archive copy of at accessed 2026-09-29; Centers for Disease Control and Prevention, "Transcript – Update on CDC's Cyclosporiasis Response – 7/14/26," CDC Newsroom, 2026, accessed 2026-09-29 go to source 1 ↗ go to source 2 ↗ go to source 3 ↗ go to source 4 ↗ go to source 5 ↗ go to source 6 ↗ go to source 7 ↗ go to source 8 ↗ go to source 9 ↗ go to source 10 ↗ go to source 11 ↗
Working notes
Notes made while writing and checking this brief, shown as written. They use working shorthand.
Distinct from `food-safety-pathogen-biosensor-real-world-validation` (which covers electrochemical biosensor matrix interference for bacterial pathogens that CAN be cultured). Cyclospora presents a different detection challenge: it is a parasite with no in vitro culture system (Almeria et al. 2019), so detection leans on amplification-based approaches, and these struggle on produce matrices. Related to `health-tb-poc-diagnostic-sputum-barrier` (analogous matrix interference problem in a different domain — sputum inhibits TB diagnostics, produce inhibits Cyclospora diagnostics). Source-bias note: the cited proceedings report what individual speakers said; one speaker, Susan T. Mayne, formerly of FDA, said that FDA is working to develop the capacity to sequence parasites such as Cyclospora cayetanensis and that more research is needed on pathogen prevalence and mitigation in fresh produce; the binding constraint is tagged technical (parasite biology limits detection approaches) combined with not-attempted (genomic tools for parasites are still being developed).
Reconciliation 2026-09-29: Fact repair after a site review read this write-up against both of its sources. Both were fetched in full on 2026-09-29. The first is The Food Forum 30th Anniversary: Proceedings of a Symposium (2024), all chapters, from https://nap.nationalacademies.org/read/27771/chapter/4 and its neighbouring chapter pages. The second is Accelerating the Use of Pathogen Genomics and Metagenomics in Public Health: Proceedings of a Workshop (2025), all chapters, from https://nap.nationalacademies.org/read/29103/chapter/1 onward; the cited catalog address now redirects to the National Academies site. The first source mentions Cyclospora once, on page 11, where Susan T. Mayne says FDA is working to develop the capacity to sequence viruses and parasites, such as Cyclospora cayetanensis, that cause foodborne illness. The second source does not mention Cyclospora at all. Neither source describes how Cyclospora is detected on produce. The changes: (1) The text said Cyclospora has caused "annual multistate outbreaks" in "the US and Canada since 2013" and causes illness "lasting weeks." None of this is in either source; the sentence now says it causes foodborne illness and has been linked to outbreaks from fresh produce. (2) "Over 2,200 confirmed cases in the US in 2023 alone, primarily through imported fresh produce" is in neither source and was removed. (3) "Produce shipments that make hundreds of people sick routinely test negative" is in neither source; the number and "routinely" were removed. (4) The text said Cyclospora "cannot be cultured" and that its oocyst wall "defeats standard extraction methods." Neither source says so; the sentence now says it is hard to grow and hard to extract. "E. coli O157:H7" now reads "E. coli," which is how the first source names it. (5) The text said FDA "cannot" confirm sources, sample imports or verify controls, that contaminated shipments are identified "only" through epidemiological investigation, and that contaminated produce enters the food supply during "every" investigation. Neither source says so; these were softened. (6) The text said Cyclospora genomics are "so underdeveloped that FDA cannot yet reliably sequence the parasite." The first source says FDA is working to develop the capacity to sequence parasites such as Cyclospora; the sentence now says that. (7) Removed because they are in neither source: the reference to FDA BAM Chapter 19b; berry pigments, chlorophyll and biofilms as the causes of PCR inhibition; the raspberry and cilantro examples; the sentence on immunomagnetic separation, Cryptosporidium and the lack of commercial antibodies; the 8–10 µm size and UV autofluorescence staining; and "No rapid or field-deployable test exists for any sample type." (8) In the notes above, "NASEM identifies this as a priority research gap" was wrong: the proceedings report what speakers said and do not name Cyclospora detection as a priority. The claim that Cyclospora research funding has lagged is in neither source. Both were replaced with what Mayne said. Confirmed against the sources and left as written: the Source line's titles and years (2024 and 2025); the Food Forum and the Food and Nutrition Board as the body behind the first source; whole genome sequencing as an established tool for bacterial foodborne pathogens such as Salmonella and E. coli. NOT supported by either source and left in softened form for a later decision: the general account of why detection on produce is hard (PCR sensitivity, oocyst recovery, microscopy). The H1 and the short title also rest on that account; they were left as written because this round changes titles only when a fact in them is shown to be wrong, and the sources are silent rather than contrary. The suggestions for student teams were not checked against the sources because they are advice. The second source comes from the Forum on Microbial Threats, not the Food Forum; the Source line was left as written. Later the same day the editor asked for the titles to be checked. FDA's Cyclospora Prevention, Response and Research Action Plan page, fetched on 2026-09-29, says "FDA has posted its recommended methods for detecting Cyclospora in fresh produce and agricultural water. The fresh produce method is available in the BAM, chapter 19b," that "there is still a critical need for such test kits to become available for industry," that "FDA has initiated a number of studies in the in vitro propagation of the parasite," and that "In 2024, FDA and CDC began building a genotype database which now includes 348 genetically, geographically, and epidemiologically diverse specimens." So the old titles, which said FDA cannot reliably detect the parasite and cannot find it on lettuce, do not hold: FDA has a laboratory method. The gap the FDA page describes is a test kit for industry, a way to grow the parasite, and genotyping to link cases to foods. The main title and the short title now say that, one sentence citing the FDA page was added to the Problem Statement, and the page was added to the Source line. Genes untouched.
Reconciliation 2026-09-29 (re-sourcing): The editor asked for the claims removed or softened in the round-5 repair above to be looked for in primary sources and put back where a source states them. Every source below was downloaded and read on 2026-09-29; nothing was restored from memory. Restored: (1) The illness lasts weeks. CDC's DPDx page (https://www.cdc.gov/dpdx/cyclosporiasis/index.html) says "Untreated infections typically last for 10–12 weeks and may follow a relapsing course," and the text now says that. (2) Outbreak history. The old text said annual outbreaks in the US and Canada "since 2013." The sources give an earlier date: Almeria, Cinar and Dubey's 2019 review in Microorganisms (read at Europe PMC, PMC6780905) says "In the mid-1990s, C. cayetanensis was recognized as the causative agent of multistate outbreaks of diarrheal illness in the USA and Canada" and "Most outbreaks due to C. cayetanensis described to date have been related to fresh produce consumption"; DPDx says "Outbreaks have been identified nearly every year since the mid-1990s" in the United States; and FDA's Cyclospora action plan page says "most of the domestically-acquired (non-travel related) cyclosporiasis outbreaks in the U.S. have been primarily linked to imported fresh produce such as raspberries, cabbage, basil, cilantro, parsley, broccoli, snow peas, sugar snap peas, lettuce and other leafy greens." The text now says mid-1990s, not 2013. (3) The 2023 case count. The archived CDC page "Cyclosporiasis Illnesses in the United States, 2023" (Internet Archive copy of December 14, 2023, of https://www.cdc.gov/parasites/cyclosporiasis/outbreaks/2023/index.html; the live address now returns "Page Not Found") says "41 jurisdictions, including 40 states and New York City, have reported a total of 2,272 laboratory-confirmed cases of cyclosporiasis. These individuals had not traveled outside of the United States during the 14 days before they got sick," with onsets April 1 to August 31 and 186 hospitalized. The old "over 2,200" now reads 2,272 with that scope. The old "primarily through imported fresh produce" is not on the 2023 page, which links only 20 of the cases to imported broccoli; the imported-produce statement now rests on the FDA page and is stated at FDA's scope (most domestically acquired outbreaks) in the Problem Statement. (4) Cannot be cultured. Almeria et al. say "There are no animal models, and/or in vivo and in vitro culture systems to facilitate C. cayetanensis research" and "only very limited biological material—namely oocysts isolated from clinical stool samples—is available for research." The text now says that, in the Problem Statement and the Source Notes. (5) Sequencing. The CDC media briefing transcript of July 14, 2026 (https://www.cdc.gov/media/releases/2026/transcript-update-on-cdcs-cyclosporiasis-response-7-14-26.html) quotes CDC's Dr. Biggerstaff: "there's not currently whole genome sequencing available to help match a contaminated product to the outbreak strain ... federal partners use targeted genotyping, which is useful for detection but not as fast and precise as whole genome sequencing that is used for traditional bacterial pathogens. This is why cyclosporiasis investigations generally take longer to link cases to each other and identify a potential source. And in some cases, a specific source may never be identified." A sentence saying that, dated to the briefing, was added to Why This Matters beside the round-5 sentence. (6) BAM Chapter 19b and PCR inhibition. Almeria et al. confirm that FDA's Bacteriological Analytical Manual Chapter 19B holds the validated wash, DNA extraction and real-time PCR method for produce, and that "the methods used for clinical samples are not always extrapolatable for detection in produce" and "Usually low numbers of oocysts are detected in naturally contaminated produce." Bartosova, Koudela and Slana's 2021 review in Food and Waterborne Parasitology (read at Europe PMC, PMC8209397) says of raspberries and strawberries that "PCR analysis is challenging due to the presence of many inhibitory substances and the low concentration of parasitic agents" and that qPCR inhibition has been observed with cilantro. The text now says that. The old causes (berry pigments, chlorophyll, biofilms) and "raspberry drupelets, cilantro leaf whorls" are in neither source and stay out. (7) Antibodies. Almeria et al.: "The isolation and concentration of C. cayetanensis oocysts using antibody-specific coated beads, as used for the detection of Cryptosporidium parvum, will likely improve efficiency, but antibodies are not yet commercially available." The sentence is back in that form. (8) Microscopy. Almeria et al.: "Due to the small size (8–10 µm) and round shape of the oocysts, they can be confused with amoebae or inflammatory cells, and alternative microscopic methods are required to achieve a higher detection sensitivity," and "Strong auto fluorescence of Cyclospora oocysts is a useful microscopic test for identification"; DPDx gives 7.5–10 µm and says the oocysts "will autofluoresce under ultraviolet (UV) microscopy." The sentence is back at that scope; because Almeria et al. say this in their section on clinical (stool) samples, the sentence now says "in stool samples". Every source named in this note was fetched a second time on 2026-09-29 (the two CDC pages through Internet Archive copies of 2026-08-29 and 2026-09-27, since cdc.gov refused the direct request) and each quoted statement was found where this note says it is. Searched for and left out: "produce shipments that make hundreds of people sick routinely test negative" (no source found that says this; the FDA page reports 167 surveillance samples of herbs and bagged greens in 2026 that were all negative, which is a different statement); "FDA cannot" confirm sources, sample imports or verify controls, and "only" and "every" in the sentence about epidemiological investigation (the CDC briefing supports slower investigations and sometimes no source found, which is now stated, but not the absolute wording); "No rapid or field-deployable test exists for any sample type" (the FDA page says a rapid test kit was developed with a company that is no longer in operation and that a kit for industry is still needed, which the Problem Statement already says; no source says none exists for any sample type); the oocyst wall "defeats standard extraction methods" (Almeria et al. describe the wall as thin and bilayered and say the parasite is highly resistant to sanitizers, not that its wall defeats extraction); "since 2013" (the sources say mid-1990s); and "Cyclospora research funding has historically lagged" (Almeria et al. call the lack of culture systems a "major bottleneck for research"; no source says funding lagged). Genes untouched.