Although travelers to tropical countries may be at increased risk, infection can be acquired in such countries as the United States and Canada. The risk may vary with season. Some evidence suggests that infection is most common in spring and summer. Cyclospora infects the small intestine and typically causes an illness characterized by watery diarrhea, with an average of about six to seven stools per day. Other symptoms can include loss of appetite, weight loss, bloating, increased gas, stomach cramps, nausea, vomiting, tiredness, muscle aches and low-grade fever.
Some persons notice flu-like symptoms before they notice the gastrointestinal symptoms.
Some persons infected with Cyclospora do not develop any symptoms. The length of time between becoming infected and developing symptoms probably averages at least several days and quite commonly is about a week. However, both shorter and longer intervals have been reported. If not treated, the illness may last for a few days to a month or longer and may come back one or more times. It is not known whether persons with compromised immune systems, such as persons who have AIDS, more commonly develop severe illness if infected with Cyclospora .