Bulletin #3111, Cyclospora and Cyclosporiasis: Understanding a Food-borne Parasite and How to Reduce Your Risk

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By Gulsun Akdemir Evrendilek, Associate Extension Professor and Seafood Technology and Food Safety Specialist, University of Maine Cooperative Extension.

Reviewed by Dr. Denise Skonberg, Professor of Food Science, School of Food and Agriculture, University of Maine and Lindsay Werner, Inspection Process Analyst Coordinator, Maine Department of Agriculture.

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Cyclospora in the News

Cyclospora cayetanensis continues to be an important cause of food-borne illness in the United States, with outbreaks reported most years, particularly during the spring and summer months. These outbreaks are often linked to fresh produce consumed raw, such as leafy greens, herbs, and berries. Although the specific food source is not always identified, recurring outbreaks highlight the importance of food safety practices throughout the production chain and remind consumers that fresh produce can occasionally become contaminated with disease-causing parasites.

Unlike bacterial food-borne illnesses such as salmonellosis caused by Salmonella ssp. or listeriosis caused by  Listeria monocytogenes, cyclosporiasis is caused by a microscopic parasite C. cayetanensis with a unique life cycle and transmission pattern. Understanding how Cyclospora contaminates food can help consumers make informed decisions to reduce their risk of illness.

What Is Cyclospora cayetanensis?

C. cayetanensis is a microscopic parasite that infects the small intestine and causes an illness known as cyclosporiasis. Humans are currently the only confirmed natural host for C. cayetanensis. Unlike many other food-borne pathogens, the parasite cannot multiply in food after contamination. Instead, people become infected by swallowing mature oocysts (eggs) that have contaminated food or water.

The parasite is found worldwide but is more prevalent in tropical and subtropical regions, where sanitation infrastructure may be inadequate. In the United States, most illnesses occur during seasonal outbreaks linked to contaminated fresh produce. Although imported produce has been associated with many previous outbreaks, domestically grown produce has also been implicated. Preventing contamination depends on maintaining good sanitation practices throughout the entire farm-to-table continuum.

How Does Produce Become Contaminated?

One of the most distinctive features of Cyclospora is its life cycle. Infected people shed immature oocysts in their feces. These freshly excreted oocysts are not immediately infectious. Under favorable environmental conditions, they require approximately 7–14 days to mature before they can cause infection. Because of this delay, direct person-to-person transmission is considered unlikely (Figure 1).

Circular diagram of the Cyclospora cayetanensis life cycle, described in the figure caption.
Figure 1. Life cycle of Cyclospora cayetanensis. A circular, six-step diagram shows the parasite’s repeating life cycle. An infected person sheds immature, noninfectious oocysts in their feces. The oocysts are not immediately infectious. After entering the environment, they require approximately seven to 14 days under favorable conditions of temperature, humidity and time to mature and become infectious. Mature oocysts may contaminate produce or water through fecal contamination of soil, irrigation water or postharvest handling. A new infection occurs when a person consumes contaminated food or water containing infectious oocysts, beginning the cycle again. Humans are currently the only confirmed natural host for Cyclospora cayetanensis.

Most contamination occurs before produce reaches consumers. Human fecal waste can contaminate agricultural environments through untreated or inadequately treated sewage, contaminated irrigation water, floodwater, or contaminated water used during postharvest washing or packing. In contrast, direct contact by an infected food handler is considered highly unlikely, as freshly shed oocysts require 7–14 days in the environment to become infectious. Because Cyclospora oocysts are shed in a noninfectious form and require approximately 7–14 days in the environment to become infectious, contamination from an infected food handler is considered much less likely than contamination occurring before harvest. Poor sanitation and inadequate wastewater management may allow mature oocysts to reach fields where fruits and vegetables are grown (Figure 2). Once oocysts adhere to produce surfaces, they can be difficult to remove completely by washing.

Diagram of the Cyclospora cayetanensis contamination pathway, described in the figure caption.
Figure 2. Cyclospora cayetanensis contamination pathway. A seven-step diagram traces contamination from left to right, beginning with an infected person and ending with a consumer. An infected person sheds immature, noninfectious oocysts in their feces. Untreated or inadequately treated human waste may enter the environment through sewage leaks, open defecation or floodwater, contaminating surface water, irrigation water or agricultural soil. After the oocysts mature in the environment and become infectious, they can adhere to fruits and vegetables in the field or during postharvest handling most notably through contaminated wash water or packing equipment, rather than through direct handling by infected workers. The oocysts may survive harvesting, sorting, washing, packing, distribution and normal storage, allowing contaminated produce to reach grocery stores and restaurants. People become infected when they consume raw produce or water contaminated with mature, infectious oocysts.

Signs and Symptoms

Symptoms usually develop about one week after exposure, although illness may begin as early as two days or more than two weeks after consuming contaminated food or water.

The most common symptom is prolonged watery diarrhea. Other symptoms may include abdominal cramping, nausea, loss of appetite, fatigue, weight loss, bloating, muscle aches, and low-grade fever. Some individuals experience symptoms that improve and then return over several weeks.

Young children, older adults, and people with weakened immune systems may develop more severe or prolonged illness. Without treatment, symptoms may persist for weeks or even months.

Diagnosis and Treatment

Because the symptoms of cyclosporiasis resemble those of many other gastrointestinal illnesses, laboratory testing is needed to confirm infection. Healthcare providers may request specialized stool tests or multiple gastrointestinal tests designed to detect Cyclospora.

The recommended treatment is the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX). Most healthy individuals respond well to treatment, although people with weakened immune systems may require longer courses of therapy.

Foods Commonly Associated with Outbreaks

Over the past three decades, cyclosporiasis outbreaks in the U.S. have most frequently been associated with fresh produce consumed raw. Foods linked to outbreaks include:

  • Leafy greens and salad mixes 
  • Cilantro 
  • Basil 
  • Parsley 
  • Green onions 
  • Raspberries and blackberries 
  • Snow peas and sugar snap peas 

Because fresh produce often has a short shelf life, contaminated products may no longer be available by the time illnesses are recognized, making outbreak investigations particularly challenging.

Why Isn’t Washing Produce Enough?

Consumers are often surprised to learn that washing fruits and vegetables cannot completely eliminate Cyclospora. Although rinsing produce under clean running water is always recommended because it removes dirt and may reduce some microorganisms, Cyclospora oocysts can adhere tightly to the surfaces of fresh produce.

Routine chemical disinfection or sanitization is unlikely to kill C. cayetanensis. Washing fresh produce thoroughly under clean running water is recommended but cannot guarantee removal of the parasite. When practical, cooking the produce to an internal temperature of at least 70°C (158°F) can inactivate Cyclospora. 

What Can Consumers Do?

Although consumers cannot completely eliminate the risk of cyclosporiasis, they can reduce their exposure by following safe food handling practices and staying informed about food recalls and outbreak investigations.

Wash your hands with soap and water before preparing or eating food to reduce the spread of many food-borne pathogens. Rinse fresh fruits and vegetables thoroughly under clean running water before cutting or serving them; however, washing alone does not reliably remove C. cayetanensis oocysts from contaminated produce. Refrigerate perishable fruits and vegetables promptly to maintain overall food quality and prevent the growth of other microorganisms, although refrigeration is not known to inactivate Cyclospora or prevent oocyst maturation sufficiently to reduce the risk of cyclosporiasis. To minimize cross-contamination, keep fresh produce separate from raw meat, poultry, and seafood during storage and preparation.

Stay informed about food recalls and public health advisories issued by the Centers for Disease Control and Prevention (CDC) and U.S. Food and Drug Administration (FDA), particularly during the summer months when outbreaks are more common. If you develop prolonged watery diarrhea, especially after eating fresh produce or traveling to an area where cyclosporiasis is common, contact your healthcare provider promptly.

Key Take-Home Messages

  • C. cayetanensis is a microscopic parasite that causes the diarrheal illness cyclosporiasis. 
  • Infection occurs by consuming food or water contaminated with mature oocysts, most often on fresh produce eaten raw. 
  • Because oocysts require time to mature in the environment, direct person-to-person spread is unlikely. 
  • Washing produce is important but does not reliably eliminate C. cayetanensis. 
  • Preventing contamination through safe agricultural water, proper sanitation, and good food handling practices remains the most effective way to reduce illness. 
  • Consumers should follow food recall notices and seek medical care if symptoms persist.

Additional Resources

Selected References

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Generative AI tools were used to assist with the development of some visual elements and to support editing for clarity and accessibility. All scientific content was reviewed, verified and approved by the author(s), who are responsible for the accuracy of this publication.

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