Cyclospora cayetanensis, a coccidian protozoan, causes a diarrheal illness first described in humans in 1979.


  • Worldwide distribution, with areas of endemic infection (Nepal, Peru, Haiti, Guatemala, Indonesia)
  • People living in endemic areas have a shorter illness or may be asymptomatic carriers.
  • Cyclospora can be an opportunistic infection in human immunodeficiency virus patients.
  • In the United States, infection occurs primarily in spring and summer.
  • In the United States and Canada, cases are associated with consumption of imported fresh produce.

General Prevention

  • Fresh produce, especially raspberries, cilantro, and salad mixes, should be washed thoroughly before being eaten, although this still may not entirely eliminate the risk of transmission.
  • Avoid consumption of waste water and, in endemic areas, avoid consumption of tap water.


  • Infected patients excrete noninfectious unsporulated oocysts in their stool.
  • Sporulation then occurs days to weeks after release into the environment.
  • Ingestion of sporulated oocysts occurs and sporozoites are released that invade the intestinal epithelial cells.
  • Sporozoites develop into trophozoites, which undergo schizogony and form merozoites.
  • Merozoites may develop into macro- or microgametes, which become fertilized, resulting in oocysts.
  • Entire life cycle is completed in the host.
  • Incubation period is between 2 and 14 days, with an average of 7 days.


  • Outbreaks have been associated with the consumption of raspberries, mesclun (young salad greens), salad mixes, cilantro, and basil.
  • Infection occurs through the consumption of contaminated food and water.
  • Transmission does not occur through person-to-person spread.



  • Fever
    • Low-grade fever is common.
  • Clinical prodrome
    • Acute onset of diarrhea is typical, but a flulike prodrome may occur.
  • Nature of the diarrhea
    • Profuse, nonbloody, watery diarrhea that may be foul smelling
    • Can alternate with constipation
  • Other symptoms experienced:
    • Abdominal cramping
    • Fatigue
    • Anorexia
    • Flatulence
    • Vomiting
  • Foods that have been consumed in the past 2 weeks
    • Illness has been attributed to contaminated raspberries, water, mesclun, salad mix, cilantro, and basil.

Physical Exam


  • Due to profuse diarrhea
  • Signs of dehydration (tachycardia, dry mucous membranes, sunken eyes, poor skin turgor, and weight loss) may be present.

Differential Diagnosis

  • Cryptosporidium
    • Outbreaks are associated with contaminated water sources (municipal pools).
    • Person-to-person transmission may occur.
    • Clinically indistinguishable from Cyclospora
  • Cystoisospora belli
    • Outbreaks are associated with food and water.
    • Clinically indistinguishable from Cyclospora, although fever may be more common
  • Microsporidia
    • Outbreaks are associated with contaminated water sources.
    • Chronic diarrhea occurs in immunocompromised patients, especially HIV patients.
    • Fever is uncommon.
  • Giardia lamblia
    • Community epidemics are associated primarily with contaminated water sources.
    • Person-to-person transmission may occur and has led to outbreaks in day care centers.
    • Clinical presentation may vary from occasional acute watery diarrhea to a severe, protracted diarrheal illness.
  • Viral gastroenteritis
    • Rotavirus
    • Adenovirus
  • Bacterial gastroenteritis
    • Clostridium difficile
    • Vibrio cholerae and non-cholerae Vibrio species
    • Escherichia coli (especially toxin-producing strains)
    • Shigella species
    • Salmonella species
    • Yersinia enterocolitica
    • Campylobacter species

Diagnostic Tests and Interpretation

Initial Tests

  • Ova and parasites with modified acid-fast staining
    • Identification of Cyclospora, Cystoisospora, and Cryptosporidium
    • Three samples are preferable due to intermittent shedding.
  • Ova and parasites: identify common protozoans including Giardia
  • Cryptosporidium and Giardia antigen test: immunoassay with high sensitivity and specificity
  • Electron microscopy of stool: gold standard for diagnosing microsporidia
  • Bacterial stool cultures: identify common bacterial pathogens
  • Stool for C. difficile PCR: identify a common cause of diarrhea
  • Gastrointestinal multiplex nucleic acid testing: simultaneous qualitative detection and identification of multiple viral, parasitic, and bacterial nucleic acids in stool specimens from individuals with gastroenteritis (some panels include Cyclospora)
  • Electrolytes, blood urea nitrogen, creatinine: may be helpful in some cases to determine extent of dehydration


Medication (Drugs)

  • Immunocompetent patient: trimethoprim-sulfamethoxazole (5 mg/kg) IV/PO twice a day for 7 to 10 days
  • HIV patient: trimethoprim-sulfamethoxazole 3 times a day for 10 days and then prophylactic dosing 3 times per week to prevent relapse
  • Ciprofloxacin or nitazoxanide for 7 days may be alternatives in patients with sulfa allergy.
  • Based on severity of dehydration, treatment with IV fluids may be indicated.

Inpatient Consideratons

Moderate to severe dehydration should warrant admission.

Ongoing Care

Follow-Up Recommendations

Patient Monitoring

  • Infected patients need to be observed closely for dehydration.
  • Relapse may occur in HIV patients, so close follow-up is essential.


  • Most cases are self-limited.
  • Diarrhea may last up to 3 months in untreated patients who acquired the parasite in a foreign country where Cyclospora is endemic.
  • In U.S. outbreaks, the average duration of diarrhea ranged from 10 to 24 days.
  • Relapses may occur in untreated patients.
  • Patients with HIV have more severe and prolonged diarrhea, which may recur.


  • Dehydration and weight loss are the most common complications.
    • Severe, prolonged diarrhea may lead to dehydration.
    • Malabsorption of d-xylose and excretion of fecal fat occurs, leading to weight loss.
  • May cause ascending biliary tract disease in AIDS patients
  • Rare associated complications
    • Guillain-Barré syndrome
    • Reactive arthritis

Additional Reading

  1. Centers for Disease Control and Prevention. Outbreaks of cyclosporiasis—United States, June–August 2013. MMWR Morb Mortal Wkly Rep. 2013;62(43):862.  [PMID:24172881]
  2. Herwaldt BL. Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s. Clin Infect Dis. 2000;31(4):1040–1057.  [PMID:11049789]
  3. Legua P, Seas C. Cystoisospora and Cyclospora. Curr Opin Infect Dis. 2013;26(5):479–483.  [PMID:23982239]
  4. Ortega YR, Sanchez R. Update on Cyclospora cayetanensis, a food-borne and waterborne parasite. Clin Microbiol Rev. 2010;23(1):218–234.  [PMID:20065331]



007.5 Cyclosporiasis


A07.4 Cyclosporiasis


240372001 Cyclosporiasis (disorder)


  • Q: Does routine ova and parasites testing detect Cyclospora?
  • A: Rarely. Therefore, modified acid-fast staining must be done to improve the laboratory’s ability to detect the oocysts.
  • Q: Can person-to-person transmission occur in Cyclospora illness?
  • A: No. It takes days to weeks for oocysts to sporulate and become infectious.
  • Q: Can animals/pets be affected by this same pathogen?
  • A: Humans are the only natural hosts of Cyclospora infection.


Jessica R. Newman, DO

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