The parasite, Cyclospora, is a newly recognized infectious organism, which causes acute gastroenteritis.  This coccidian protozoan parasite known as Cyclospora cayetanensis, is composed of only one cell.  It is too small to be seen with the naked eye (only 8-10 microns in diameter).  Cyclosporiasis is a relatively new diarrheal illness.  Ashford first reported it in1979 in Papua New Guinea.  Cases have been reported with increased frequency from various countries since the mid 1980’s, perhaps because of the increasing use of acid-fast stains to identify other coccidian in stool specimens and the recognition that similar organism of different sizes represent different genera.   It has been the cause of annual seasonal outbreaks of persistent diarrhea in travelers and expatriates in Nepal and Peru, and the distribution of this organism appears to be worldwide.


The epidemiology of the intestinal spore-forming protozoa is not fully understood.  Work in this area has been hampered by a lack of complete surveillance, widespread serologic surveys and extensive stool examinations.  Cyclospora infections have been identified in otherwise healthy travellers to developing countries, consumers of perishable food products and water contaminated with Cyclospora, and children in developing countries.

Cyclospora has now been described and associated with diarrheal illness in North, Central and South America, the Caribbean, Africa, Bangladesh, Southeast Asia, Australia, England, Spain, and Eastern Europe. Areas endemic with cyclosporiasis are mainly in Central and South America and Asia. Infections can occur sporadically or in clusters. Most infections occur in these endemic areas or in travellers returning from these regions. Much of the information about Cyclospora comes from study groups in Nepal, Haiti and Peru. However, infections and outbreaks indigenous to other areas, including recent outbreaks in the United States, have been reported. The prevalence of Cyclospora in North America and the United Kingdom is estimated at levels lower than .5%.

Cyclospora infection appears to be very seasonal, although it has different patterns in different parts of the world. Certain ranges of temperature, humidity and other environmental factors appear to allow for survival of oocysts and sporulation. In Nepal and Kathmandu it coincides with the rainy season from May through September. In Haiti infection is more common in the drier and cooler months of the first quarter of the year. In coastal Peru, infections occur mainly from December through May and sometimes into June or July. In Guatemala, research shows a peak in June but a heightened incidence from May through August. In Indonesia the peak season for the parasite is during the wet season of October through May.

Recent Outbreaks

The first documented US cases were noted in four travelers returning from Haiti and Mexico in 1986.

Cook County Hospital in Chicago reported an outbreak that was apparently caused by contamination of a water storage tank by an unknown means.

A major outbreak occurred in the United States and Canada in the spring and summer of 1996.  Cases were reported in 20 states, the District of Columbia, and 2 provinces of Canada, and the estimated total of infected persons was 1465.  This number was greater that the total number of cyclosporiasis cases that had been reported worldwide thus far.  The source of the outbreak was associated with contaminated raspberries from Guatemala.

In 1997 there were other outbreaks in the United States associated with consumption of fresh mesclun.  The source of this mesclun greens was traced to Peru.  There have also been outbreaks traced to fresh basil.


Various modes of transmission of the parasite to humans have been suggested.  The infection can clearly be contracted through consumption of fecally contaminated water or food.  Infected persons excrete the oocyst stage of Cyclospora in their feces. When excreted, oocysts are not infectious and may require from days to weeks to become infectious (i.e., to sporulate). Therefore, transmission of Cyclospora directly from an infected person to someone else is unlikely.

However, indirect transmission can occur if an infected person contaminates the environment and oocysts have sufficient time, under appropriate conditions, to become infectious. For example, Cyclospora may be transmitted by ingestion of water or food contaminated with oocysts. Outbreaks linked to contaminated water, as well as outbreaks linked to various types of fresh produce, have been reported in recent years.


The most typical sign of Cyclospora infection is watery, nonbloody diarrhea that begins days or weeks after foreign travel. The incubation period for Cyclospora is longer than for most enteric disease, usually about one week.  Onset may be abrupt or gradual and symptoms include nausea, vomiting, anorexia, bloating, abdominal cramping, increased gas, watery diarrhea, malaise and weight loss.  Fatigue and anorexia are extremely predominant and may help distinguish Cyclospora infection from other pathogens. Patients have a median of six stools each day.  Patients may also experience relapses and remission of the diarrhea, with the duration of symptoms ranging from approximately 1 to 7 weeks.  The symptoms tend to be more prolonged in patients with AIDS.  Shedding of the organism has been reported to continue for 7 to 70 days.


The disease appears to be self-limiting.The recommended treatment for infection with Cyclospora is a combination of two antibiotics, trimethoprim-sulfamethoxazole (TMP/SMX), also known as Bactrim*, Septra*, or Cotrim*. TMP/SMX has been shown in a placebo-controlled trial to be effective treatment for Cyclospora infection. Adults should receive TMP 160 mg plus SMX 800 mg (one double-strength tablet) orally twice a day for 7 days. Children should receive TMP 5 mg/kg plus SMX 25 mg/kg twice a day for 7 days. Patients with AIDS may need higher doses and long-term maintenance treatment. People who have diarrhea should rest and drink plenty of fluids.

No alternative antibiotic regimen has been identified yet for patients who do not respond to or are intolerant of TMP/SMX (e.g., allergy to sulfa drugs). Anecdotal or unpublished data suggest that the following drugs are ineffective: albendazole, trimethoprim, azithromycin, nalidixic acid, norfloxacin, ciprofloxacin, tinidazole, metronidazole, quinacrine, tetracycline, doxycycline, and diloxanide furoate.


Laboratory diagnosis


Currently, the most practical diagnostic method consists of the identification of oocysts in stool specimens by light microscopy using special stains.  Other methods are also available or under investigation. A single negative test does not definitively rule out the possibility of infection; two or three more specimens may be required for diagnosis.




There is no vaccine available for Cyclospora infection.

Avoiding food or water that may be contaminated with feces may help prevent Cyclosporiasis.  When travelling to developing countries, persons should not eat foods such as fruits or vegetables that are not cooked or peeled and avoid drinking untreated water.



Nadine Parsons RN

Region of Waterloo Public Health

Waterloo, ON.

(519) 8832006 (5271)






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