Cyclospora is believed to be the source of 71 illnesses in Iowa and 35 in Nebraska.
Past cases of cyclospora have been linked with fresh produce and vegetables, said the Iowa Department of Public Health (IDPH).
People become infected with cyclospora by consuming food or water contaminated with the parasite.
Only three cases had been reported in the past 12 years, according to the IDPH annual report.
Fresh fruit and veg source?
Cyclospora illness is traced to consumption of fresh fruits and vegetables contaminated with the parasite; this investigation currently indicates fresh vegetables, not fruit, may be the source of illness.
IDPH is working with local public health agencies to interview individuals who are ill to determine if there is a common food exposure that would indicate the source of illness.
Most of the illnesses in this outbreak began in mid to late June. Many people report still being ill and some have had relapses.
Cluster investigations are continuing to determine what the well people did not eat, with the IDPH and Centers for Disease Control and Prevention (CDC).
Past CDC findings
The CDC said it was notified of 1,110 laboratory-confirmed sporadic cases of cyclosporiasis during 1997-2008.
372 case-patients (33.5%) had a documented history of international travel during the two week period before symptom onset or diagnosis, 398 (35.9%) reported no international travel, and 340 (30.6%) had an unknown travel history.
For 317 (85.2%) of the case-patients with a known history of international travel; 142 (44.8%) had traveled to Mexico (60 people), Guatemala (44 people), or Peru (38 people).
Among the 398 case-patients classified as domestically acquired cases, 124 people (31.2%) lived in Florida, and 64 people lived either in NYC (49 people) or elsewhere in New York state (15 people).
Cyclospora infection causes a watery diarrhoea that lasts an average of 57 days, if untreated.
* article updated 16/7/13 with new case count