Cyclospora is a parasite composed of one cell, too small to be seen without a microscope. The organism was previously thought to be a blue-green alga or a large form of Cryptosporidium. Cyclospora cayetanensis is the only species of this organism found in humans.
The first known human cases of illness caused by Cyclospora infection (that is, cyclosporiasis) were first discovered in 1977. An increase in the number of cases being reported began in the mid-1980s, in part due to the availability of better diagnostic techniques. Over 15,000 cases are estimated to occur each year in the United States.
The first outbreak in North America occurred in 1990 from contaminated water. Since then, several outbreaks of cyclosporiasis have been reported in the U.S. and Canada, many associated with eating fresh fruits or vegetables. In some developing countries, cyclosporiasis is common among the population and travelers to those areas have become infected as well.