Due to a steady increase of foodborne Cyclospora cayetanensis infections in recent years, the U.S. Food and Drug Administration (FDA) charged the National Advisory Committee on Microbiological Criteria for Foods (NACMCF) with producing a report that provides information on the factors that contribute to the contamination of produce by the parasite, as well as recommendations for a prevention and management strategy. A copy of the report was recently published by the U.S. Department of Agriculture’s Food Safety and Inspection Service (USDA’s FSIS).
NACMCF provides impartial scientific advice and peer reviews to federal food safety agencies for use in the development of an integrated, national approach to food safety systems. In addition to FDA and USDA, the U.S. Centers for Disease Control and Prevention (CDC), the U.S. Department of Commerce’s National Marine Fisheries Service, and the U.S. Department of Defense’s Veterinary Services Activity also benefit from NACMCF’s work.
Background
Cyclospora are protozoan parasites that can infect different species of mammals with remarkable host-specificity. Cyclospora has a complex lifecycle and can multiply within the infected hosts, and the parasite is characterized by environmentally hardy oocysts that are shed in stools of infected persons. The oocysts are shed unsporulated and are not infectious; however, released into the environment, unsporulated oocysts require approximately 7–14 days under certain environmental conditions to sporulate and become infectious. Oocysts are thought to be transferred to the surface of foods, specifically produce, through human fecal pollution carried by agricultural water, and subsequently infect hosts after contaminated produce is consumed.
A limitation to widespread C. cayetanensis research is the inability to directly culture or propagate the organism, and researchers rely solely on acquired oocysts to conduct research. Some work has been done to use surrogate organisms to mimic the lifecycle of C. cayetanensis, with limited positive results.
According to the recent NACMCF report, in 2020, CDC confirmed 1,241 cases of cyclosporiasis in people who had no history of international travel and experienced illness onset during May 1–August 31 of that year, which is the typical peak season for C. cayetanensis infections in the U.S. In 2019 and 2018, CDC reported 2,408 and 2,299 cases, respectively. Comparatively, between 2000 and 2017, the total number of cases reported for cyclosporiasis in the U.S. was 1,730.
In response to the rising trend of C. cayetanesis infections in the U.S., in 2021, FDA announced a plan to lessen the public health burden of foodborne illnesses caused by the parasite, which involved collaboration with NACMCF to provide information that would inform FDA’s prioritization of Cyclospora research and propose novel food safety research projects in collaboration with stakeholders. In 2022, authors from FDA also published an article with Food Safety Magazine describing recent and recurring outbreaks of cyclosporiasis, as well as the need for a comprehensive understanding of how C. cayetanensis contaminates water and produce.
Despite several efforts to develop molecular detection methods for the parasite in both food and environmental samples, and the use of such methods in epidemiological investigations and surveys to estimate the prevalence of C. cayetanensis in commodities and growing regions, there still exist several significant knowledge and data gaps that hamper the implementation of effective measures to prevent the contamination of produce with the oocysts of the parasite. FDA charged NACMCF with filling these knowledge and data gaps.
NACMCF’s Recommendations
At present, within the genus Cyclospora, only C. cayetanensis is known to infect humans. However, recent advances in genomics separated the parasite into three proposed species (including C. cayetanensis), with the two new proposed species—C. ashfordi and C. henanensis—also considered parasitic to humans. Throughout the NACMCF report, to reflect the proposed status of the new nomenclature, “C. cayetanensis” was used to refer to all three species of Cyclospora that are parasitic in humans.
C. cayetanensis oocysts are resistant to harsh environmental conditions and many chemical treatments commonly used to reduce the presence of bacterial pathogens in the specialty crop production environment and in agricultural inputs (e.g., agricultural water). Detected in association with human illness in many parts of the world, C. cayetanensis was previously considered to be a pathogen acquired during childhood in developing nations. In the U.S., cyclosporiasis was previously associated with international travel or consumption of contaminated imported foods. However, in recent years, the U.S. has seen an increase in cases and positive samples associated with domestically grown produce, both as raw agricultural commodities and fresh-cut goods. Laborers with a history of recent travel to countries where C. cayetanensis is endemic have not been ruled out as the sources of the pathogen in such outbreaks.
Since 2016, the number of cyclosporiasis cases has increased approximately threefold, often linked to the consumption of leafy greens and ready-to-eat (RTE) salads. Fecal contamination from symptomatic or asymptomatic carriers is the only known source of C. cayetanensis. The hypothesis that the parasite has become endemic in the production regions of the U.S. has yet to be sufficiently supported.
Efforts have been made to develop molecular detection methods for the parasite in both food and environmental samples. However, due to the high degree of genome-level conservation between C. cayetanensis and its close relatives that are not pathogenic in humans, results of some environmental surveys that relied solely on the PCR-based detection of ribosomal RNA genes likely overestimated the prevalence of C. cayetanensis.
NACMCF acknowledges the remaining knowledge and data gaps that stand in the way of foodborne cyclosporiasis mitigation, and the committee underscores the importance of understanding the factors the lead to contamination. NACMCF provided several recommendations to FDA in its report:
- To facilitate future research (e.g., validation of surrogates, studies on environmental persistence and attachment) and identification and validation of control strategies, NACMCF urges development of a practical method to propagate C. cayetanensis oocysts under laboratory settings.
- Due to the limited availability of C. cayetanensis oocysts, research with surrogates—especially with the close relative C. Eimeria—can be informative for identifying control strategies and learning about persistence in the production environment.
- Method development for the detection of C. cayetanensis in food and environmental samples should include the evaluation of multiple genetic targets representing different regions of the genome. Modifications to current molecular methods for the detection of C. cayetanensis should be thoroughly validated for impacts on specificity before using modified methods on food or environmental samples. Conversely, detection methods should be designed to be robust, reproducible, and tolerant of minor modifications in the methodologies (e.g., brand of equipment or reagents, minor deviations in PCR conditions, etc.) without sacrificing specificity or sensitivity.
- Given that the hypothesized likeliest source of the parasite in the food production environment (individuals with a history of recent travel to areas where infections with C. cayetanensis are common or other exposures to the parasite), preventative measures should center around clear sanitation guidelines, ensuring onsite capacity for implementing sanitation protocols (i.e., readily accessible handwashing stations with soap, etc.) and periodic training of employees.
