Those affected by cyclospora come from nine states but may have included international travel-associated cases or cases acquired from a neighbouring state, said the US Centers for Disease Control and Prevention (CDC).
No food items have been implicated to date, but public health authorities are pursuing all leads and previous outbreak investigations have implicated various types of fresh produce, said CDC.
10 people hospitalized
At least 10 persons reportedly have been hospitalized and most of the illness onset dates range from mid-June through early July.
The agency said on 28 June it was notified of two laboratory-confirmed cases of Cyclospora infection in Iowa residents who had become ill in June and did not have a history of international travel during the 14 days before the onset of illness.
Since then they have been collaborating with public health officials and the US Food and Drug Administration (FDA) to investigate an outbreak of cyclosporiasis.
States affected
The number of cases identified in each state is: Iowa (127), Nebraska (68), Texas (65), Wisconsin (4), Georgia (2), Connecticut (1), Illinois (1), Kansas (1), and New Jersey (1).
As of 22 July, CDC has been notified of more than 250 cases of Cyclospora infection in residents of Iowa, Nebraska, Texas, Wisconsin, Georgia and Connecticut.
There were 35 cases of cyclosporiasis reported in Texas from 2001 to 2010, according to the Texas Department of State Health Services.
Only three cases had been reported in the past 12 years, according to the Iowa Department of Public Health.
Illinois and Kansas have also notified CDC of one case each that may have been acquired out of state but in the US.
CDC has confirmed five cases of Cyclospora infection in its laboratories. One of those cases was confirmed via telediagnosis, which the CDC encourages to confirm cases as it allows for rapid laboratory confirmation.
It was notified of 1,110 laboratory-confirmed sporadic cases of cyclosporiasis during 1997-2008
Cyclosporais spread by people ingesting something - such as food or water - that was contaminated with the parasite.