Cyclospora Infection (Cyclosporiasis)

What is a Cyclospora infection?

Cyclosporiasis is a diarrheal illness that occurs when humans accidentally ingest the Cyclospora cayetanensis parasite. This happens by drinking or eating uncooked items contaminated with soil or water.

What causes a Cyclospora infection?

Cyclospora cayetanensis was originally described as coccidian or Cyanobacterium-like because it resembled certain algae. In fact, it is a parasite that cycles between the environment (soil) and humans during its life cycle. It survives for long periods of time in nature as an oocyst. Cyclospora oocysts can resist extreme temperatures and the usual levels of chlorine in treated water. When temperatures warm, the oocyst matures and releases the infectious forms, called sporocysts. When sporocysts are ingested by a human, they invade the epithelial cells of the small intestine. They multiply in the cells and produce new oocysts. These are excreted in feces, starting the cycle all over again.

Cyclospora cayetanensis causes disease throughout the world, but it is commonest in tropical and subtropical climates. Outbreaks in cooler areas are often caused by food imported from warmer climates. Food is at risk if exposed to soil or water that is contaminated with human feces. Fresh produce like lettuce, raspberries, basil, and snow peas have caused past outbreaks. In 2013, an outbreak involved many states, including Texas, Iowa, and Nebraska. It affected hundreds of people and was at least partially caused by bagged lettuce grown in Mexico. There have been small outbreaks in 31 states with a total of 546 people diagnosed with the infection in 2015. Two large outbreaks occurred in 2018, one due to vegetables (packaged) by Del Monte and another by salads by McDonald's, resulting in their recall from about 3,000 locations. In 2018, the CDC documented over 300 cases of Cyclospora infection associated with bagged lettuce in 15 states.

Although travel to a tropical or subtropical country is a risk factor for Cyclospora infection, the risk is relatively low. Cyclospora is not a major cause of travelers' diarrhea.

Is Cyclospora contagious?

Cyclospora is not contagious directly from person to person. Even though the oocysts are shed in stool, they take days to weeks to mature in the environment before becoming infectious. People can only be infected by eating or drinking something contaminated with mature oocysts. This is called fecal-oral transmission.

The incubation period (the time between swallowing the oocysts and the start of symptoms) is two to 14 days, or an average of 10 days.

What are the symptoms of a Cyclospora infection?

Cyclospora causes watery diarrhea that lasts more than a week, up to four weeks or more. This is called cyclosporiasis. Abdominal cramping or belly pain and fatigue are common. The infected person may have five to 15 bowel movements per day. Also common are heartburn, nausea, increased gas, decreased appetite, and weight loss. Flu-like symptoms with low-grade fever and muscle aches is less common. Symptoms are worse in those with weak immune systems, such as people with acquired immunodeficiency syndrome (AIDS).


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Diagnosis of a Cyclospora infection

Most people with persistent diarrhea will probably be evaluated first by a primary care provider, such as an internist, pediatrician, family medicine doctor, or nurse practitioner. As diarrhea continues beyond a couple of weeks, referrals may be made to a gastroenterologist or an infectious disease doctor for further evaluation and treatment.

Most cases of diarrhea are caused by viruses or bacteria that produce an illness only for a few days and resolve without specific treatment. Most people are not sick long enough to go to the doctor and have tests performed. If a person has diarrhea that is persisting beyond a week or so, there are a number of possible causes including intestinal parasites. Food, travel, and antibiotic exposures should be discussed with a health care provider, who may order stool studies. Doctors diagnose Cyclospora infections by examining the stool under a microscope and finding oocysts. Even with a lot of diarrhea, oocysts may be hard to find, because oocysts are not shed continuously. At least three stool samples should be collected 24-48 hours apart. To increase the ability to diagnose Cyclospora, special staining methods such as acid-fast stain (results are variable), polymerase chain reaction (PCR) tests, and stool specimen concentration techniques are used. Physicians must alert the laboratory to look for Cyclospora if ordering stool studies, because these tests are not routine. There is no blood test that can detect Cyclospora.

What is the treatment for a Cyclospora infection?

Cyclospora infection often goes away by itself, and mild or asymptomatic cases require no treatment. For those who require treatment, the best option is oral trimethoprim-sulfamethoxazole (TMP-SMX, also called co-trimoxazole) (Bactrim, Septra) twice daily for seven to 10 days. For those who continue to have symptoms or have persistent oocysts on stool examination, another seven-day course is usually effective. Sometimes anti-diarrheal medication is recommended, but only under the doctor's approval. For people with a sulfa allergy, there are few good options. There are reported cases where nitazoxanide (Alinia) twice daily was successful as an alternate therapy. One small study suggested that ciprofloxacin (Cipro, Cipro XR, ProQuin XR) twice daily for seven days is an option in adults. However, it has a higher failure rate compared to TMP-SMX. These medications are not approved for routine use in pregnancy. Pregnant women should check with their obstetrician (ob-gyn doctor) before taking any new prescription.

What are complications of a Cyclospora infection?

Profuse, watery diarrhea may cause dehydration. Thus, keeping up with fluids is important. Diarrhea also contains salts and potassium, so drinking fluids that contain electrolytes (such as sports drinks) may be beneficial. Some people feel loss of energy for some time after the diarrhea goes away.

What is the prognosis of a Cyclospora infection?

The prognosis of cyclosporiasis is excellent and complete recovery is anticipated. As discussed above, recovery can be hastened by the use of antibiotics in symptomatic people.

Patients who are infected with the human immunodeficiency virus (HIV), however, may relapse after treatment is stopped and should be referred to an infectious disease doctor.

Is it possible to prevent a Cyclospora infection?

General food safety practices are important to prevent many infections and food poisoning, especially while traveling in areas where sanitation is uncertain. Wash hands in disinfected or fizzy water or use alcohol-based hand sanitizer before eating. Cooked food that is served steaming hot is generally safe, but various types of undercooked or raw fruits and vegetables pose a risk of Cyclospora and other infections. A good rule of thumb for travelers is to avoid raw fruits and vegetables, or to wash and peel them personally with cleaned hands with disinfected or factory-sealed bottled water. Bottled or canned fizzy drinks are safe to drink and wash with; bubbles mean the bottle has not been refilled with tap water and sealed with glue. If a water filter is used, it must be labeled as effective against cysts or particles up to 1 micron (a measure of length equal to one millionth of a meter). Fresh produce or foods that have been handled raw, such as salsas, salad greens, or cut-up fruit on a platter, are best avoided.

Since many foods are grown or prepared outside the U.S., it is important to consider food safety at home, as well. Pre-packaged raw vegetables and fruits, especially with extra handling (for example, chopped bagged salad mix), should be thoroughly rinsed even if labeled as triple washed.

Cyclospora may cause infection more than once if contaminated food or water is ingested. Currently, there is no available vaccine to prevent infection with Cyclospora cayetanensis.

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United States. Centers for Disease Control and Prevention. "Food and Water Safety." Feb. 20, 2020. <>.

United States. Centers for Disease Control and Prevention. "Parasites -- Cyclosporiasis (Cyclospora Infection)." Mar. 12, 2020. <>.

Wright, S.G. "Protozoan Infections of the Gastrointestinal Tract." Infect Diseases of North America 26 (2012): 323-339.