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Cyclospora: An Unresolved Mystery

Jennifer K. Seltzer, PharmD

July, 2013

The Centers for Disease Control (CDC) is investigating a recent outbreak of cyclosporiasis in the United States.  On June 28, 2013, Iowa officials reported two laboratory-confirmed cases of Cyclospora infection in which residents became ill but had no history of international travel within 14 days of symptom onset.  As of July 25, 321 cases have been reported to the CDC and a collaborative effort is ongoing with public health officials of several states and the Food and Drug Administration (FDA) to determine the source of this illness.1 The Texas Department of State Health Services has corroborated 101 cases of Cyclospora in Texas as of July 26, 2013, with 17 cases in Dallas county, 16 cases in Collin county and 13 cases in Tarrant county.  Other affected Texas counties include Comal, Denton, El Paso, Ellis, Harris, Hidalgo, Hood, Johnson, Montague, Parker, Potter, Tom Green, Travis, Victoria, and Williamson.2 Most of the cases have occurred between mid-June and early July, but a specific food item has not yet been implicated.  Previous Cyclospora outbreaks in the United States, however, were linked to imported fresh produce including snow peas, basil, raspberries, and meclun lettuce.  Common events such as social gatherings have not been associated with the cases, and it is still not certain whether all reported cases are components of the same outbreak.  At least 18 patients from three states have apparently been hospitalized due to Cyclospora illness.1, 3 

         Cyclosporiasis, an intestinal illness caused by the microscopic parasite Cyclospora cayatenensis, is most commonly acquired by ingesting food or water contaminated with feces containing sporulated (infective) Cyclospora oocysts. Once infected, the human host passes unsporulated (immature, noninfective) Cyclospora oocysts in the feces. Favorable environmental conditions (e.g., temperatures of 22oC to 32oC) for days to weeks are necessary for the oocysts to sporulate, or become infective.  Because of this process, it is unlikely that the infection is transmitted through direct person-to-person contact or through ingestion of freshly contaminated food or water.1, 4, 5  The infection is most commonly characterized by watery diarrhea, as well as loss of appetite, weight loss, cramping, bloating, increased gas, nausea, and fatigue.  Other symptoms occurring less frequently may include vomiting and low-grade fever. Symptoms typically manifest an average of 7 days (range, 2 days to > 2 weeks) after ingesting sporulated oocysts.  Patients may experience relief from some symptoms while other symptoms, like diarrhea, muscle aches and fatigue, may return. Untreated patients may experience symptoms for several weeks to more than a month.1-5

         Cyclospora is diagnosed by identifying oocysts in stool specimens through acid-fast staining or polymerase chain reaction analysis.  Diagnosis can be difficult if too few oocysts are present in a stool sample, and patients may need to submit several samples collected over multiple days.  Although cyclosporiasis has been identified in many countries, the disease has been most prevalent in tropical and subtropical regions.  Health care providers should suspect Cyclospora in individuals with prolonged watery diarrhea, especially in patients who have travelled to Cyclospora-endemic regions.1, 4

       Cyclosporiasis can be treated with antibiotics, with the treatment of choice limited to trimethoprim-sulfamethoxazole (TMP-SMX) (e.g., Bactrim® , Septra® ) dosed as one double- strength tablet (160 mg/800 mg) twice daily for 7 to 10 days in immunocompetent adults.5 Although not as effective as TMP-SMX, ciprofloxacin may be considered in those patients with a sulfa allergy (500 mg twice daily for 7 days), although anecdotal reports of ciprofloxacin use in immunocompetent individuals indicate that the drug is ineffective.4, 5 Nitazoxanide has also shown efficacy in eradicating Cyclospora infections and may be considered another alternative treatment.5 People experiencing diarrhea are encouraged to rest and drink fluids.4  Cyclosporiasis in immunocompromised patients (e.g., human immunodeficiency virus) causes more serious disease and requires prolonged therapy with higher treatment doses.1

         It is not clear how food and water become contaminated with Cyclospora oocysts, but the best way to prevent cyclosporiasis is to avoid polluted materials.  Food growers are encouraged to follow good agricultural and good manufacturing practices to minimize contamination.  Iodine and chlorine treatments are ineffective in killing the Cyclospora parasite.1, 4 While produce should be thoroughly washed prior to eating, data from previous outbreaks have shown that washing does not eliminate the risk of developing cyclosporiasis.6  

People experiencing prolonged watery diarrhea who suspect they may be infected with Cyclospora should seek assistance from health care providers.  Since people who have previously experienced Cyclospora infections can be re-infected, preventive practices are key to reducing cyclosporiasis outbreaks.1


  1. Centers for Disease Control and Prevention.  Investigation of an outbreak of cyclosporiasis in the United States.  (July 26th, 2103)  Available at:  Accessed July 28th, 2013.
  2.   21 new cases of Cyclospora reported in Texas since Thursday.  (July 26th, 2013)  Available at:  Accessed July 28th, 2013.
  3. Forbes.  Cyclospora outbreak:  what you need to know.  (July 26th, 2013)  Available at:  Accessed July 28th, 2013.
  4. Centers for Disease Control and Prevention.  Parasites – cyclosporiasis (Cyclospora infection).  Available at:  Accessed July 28th, 2013.
  5. Weller PF, Leder K.  Cyclospora infection.  In: UpToDate, Basow, DS (Ed), UpToDate,
    Waltham, MA, 2013.
  6. Yo AY, Lopez AS, Eberhart MG, et al.  Outbreak of cyclosporiasis associated with imported raspberries, Philadelphia, Pennsylvania, 2000.  Emerg Infect Dis.  2002;8(8):783-8.

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