By Kelly A. Reynolds, MSPH, PhD

Many of the same pathogens transmitted by food are also transmitted via the waterborne route. Without thorough outbreak investigation, identification of a food or water source of infection may be difficult to determine. In July 2013, an outbreak of a food/waterborne protozoan parasite, Cyclospora cayetanensis, was reported with a total of 39 cases in at least two states at press time. While the multi-state nature of this particular outbreak suggests a broadly distributed food source, Cyclospora is a bug to watch relative to drinking water risks as well.

Outbreaks and illnesses
Compared to cousins Giardia and Cryptosporidium, Cyclospora is a lesser known protozoan parasite. Also spread by the fecal-oral route, previous outbreaks have been linked to food, especially berries and contaminated water.

Discovered in the early 1900s, Cyclospora were originally classified as blue-green algae. Human infections were first reported in the 1970s, followed by a rash of infections alongside the AIDS epidemic with a new population of immunocompromised persons more vulnerable to microbial infections.

Infections may lead to fatigue, nausea, fever, stomach cramps, diarrhea and substantial weight loss. Vomiting may occur but with less frequency. Even otherwise healthy individuals can experience long-term and severe illness, potentially lasting for weeks to months if untreated. Persons who are immunocompromised may experience more severe symptoms that persist even longer. Typical of protozoan pathogens, symptoms may appear to improve only to result in a series of relapses. Once infected with Cyclospora, approximately a week will pass before symptoms appear. This delayed symptomology complicates outbreak investigations, as accurate recall of one’s food and water intake a week prior is difficult. Typically when fallen ill with a stomach bug, we tend to target our last meal, but microbes don’t proliferate quite that fast.

Interestingly, Cyclospora infections are not contagious. While an infected individual will excrete oocysts in their feces, a period of time (often days to weeks) is required for the oocyst to progress to the infectious sporulation stage. Symptoms can range from nonexistent to explosive and frequent diarrhea (five to 15 bowel movements/day).

In 2011, a Cyclospora outbreak in Georgia resulted in more than 100 ill people who worked for or visited the Georgia Aquarium. All were involved with catered events where salad, tomatoes and fresh basil where commonly served. Waterborne outbreaks have been documented even in chlorinated sources (Table 1). The first reported waterborne outbreak was in a population of physicians in Chicago who were housed at a common dormitory. Stagnant water from a storage tank following a pump failure is thought to

have contributed to the transmission of cyclosporiasis; however. a food-borne route has also not been ruled out. Most cases in the current US outbreak have occurred in Iowa and Nebraska. The source of the outbreak is currently unknown but 39 people are reportedly ill with at least one hospitalized.

Drinking water risks
Even though humans are the only known reservoir of infection, Cyclospora is endemic in many regions of the world, especially tropical or subtropical areas. The organism is likely a common cause of traveler’s diarrhea. Exactly how water, or food, gets contaminated with Cyclospora is not fully understood. Similar parasites are also found in baboons, dogs, chickens, ducks and cattle but only the species Cyclospora cayetanensis causes human infection.

Researchers have also suggested that insects and nematodes could play a role is dissemination of the pathogen through mechanical transport. The US Centers for Disease Control and Prevention (CDC) has an active surveillance program for cyclosporiasis. The disease is part of a relatively short list of nationally notifiable diseases where regular and frequent reporting occurs in most states and local health departments provide timely reports to the CDC.

In the US from 1997 to 2008, 1,110 laboratory-confirmed, sporadic cases were reported, resulting in 11 hospitalizations and no deaths. Another 3,000 outbreak-associated cases were also reported during the same time frame. About a third of diagnosed sporadic cases occurred in persons who recently traveled internationally, primarily to Mexico, Guatemala or Peru. US infections in persons not associated with international travel (i.e., domestically acquired) were  concentrated in eastern and southeastern states (Florida and New York) and also accounted for about a third of the cases.

Protozoan pathogens are a particular challenge to control due to their ability to form an oocyst as part of their life cycle. These environmentally stable oocysts are resistant to chemical disinfectants, including chlorine and iodine. Other waterborne routes may include contaminated recreational or produce irrigation water supplies. Water used for pesticide application is also a potential vehicle.5

Exposure reduction
To minimize risks of microbial infections, including Cyclospora, all fruit and produce should be washed prior to consumption and especially products that are eaten uncooked. Fresh, imported produce is the most common source of the infection in the US. No commercially frozen or canned produce has been linked to cyclosporiasis.

The CDC has released a guideline for food handlers with Cyclospora infection suggesting handlers seek treatment with the antibiotic trimethoprim-sulfamethoxazole (a sulfa drug sold under the trade names Bactrim, Septra or Cotrim) and be excluded from work until diarrhea resolves. Asymptomatic food handlers are not necessarily recommended to abstain from working given the inability of Cyclospora to be directly transmitted presporulation. Optimal conditions relative to time and temperature that promote sporulation in the environment are not well understood. Similarly, while pasteurization and freezing inactivate the oocysts, also unknown are the minimal time and temperature conditions of cooking and freezing required.

Avoiding untreated or contaminated drinking water, especially when traveling to endemic regions, is the best defense against cyclosporiasis. Measuring approximately twice the size of Cryptosporidium, Cyclospora are effectively removed from source waters via municipal treatment methodologies designed for Crypto removal, if administered properly. Likewise, POU systems utilizing technologies for Crypto removal (i.e., submicron filtration, ozone, UV) are expected to remove Cyclospora.


  1. Glissmann, B. “Iowa Cyclospora outbreak rises to 39 cases,” The Global Dispatch, 11 July 2013. [Online]. Available: [Accessed 11 July 2013].
  2. Spellman, F.R. and Drinan, J.E. “Cyclospora,” in The Drinking Water Handbood, Second Edition, Boca Raton, FL, CRC Press, Taylor & Francis Group, 2012, pp. 134-136.
  3. CBS Atlanta, WSB-TV, Associated Press. “Cyclosporiasis outbreak in Georgia State of USA,” 30 September 2011. [Online]. [Accessed 11 July 2013].
  4. Rabold, J.G.; Hoge, C.W.; Shlim, D.R.; Kefford, C. et al. “Cyclospora outbreak associated with chlorinated drinking water,” The Lancet, vol. 344, pp. 1360-1361, 1994.
  5. Ortega, Y.R. and Sanchez, R. “Update on Cyclospora cayetanensis, a foodborne and waterborne parasite,” Clinical Microbiology Reviews, vol. 23, pp. 218-234, 2010.
  6. CDC, “Cyclosporiasis (Cyclospora Infection)–Prevention and Control,” 10 January 2013. [Online]. Available: [Accessed 11 July 2013].
  7. Hall, R.L.; Jones, J.L. and Herwaldt, B.L. “Surveillance for laboratory- confirmed sporadic cases of cyclosporiasis–United States 1997-2008,” Morbidity and Mortality Weekly Report (MMWR), vol. 60, no. (SS02), pp. 1-11, 2011.
  8. CDC, “Recommendations for food handlers with Cyclospora infection,” CDC, 10 January 2013. [Online]. Available: closporiasis/resources/pdf/cyclosporiasis_food_handlers.pdf. [Accessed 11 July 2013].

About the author
Dr. Kelly A. Reynolds is an Associate Professor at the University of Arizona College of Public Health. She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at [email protected]


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