The US Food and Drug Administration (FDA) has increased surveillance sampling on cilantro imported from Puebla, Mexico after it was linked to 133 cases of Cyclospora in Texas.
The agency said it will continue working with Mexican authorities to determine if there is a common farm or growing area which could have provided the fresh cilantro linked to the outbreak.
Epidemiological and traceback investigations found four restaurants in Texas, where multiple unrelated ill people reportedly have eaten.
All the ill persons in these four clusters reported having eaten a food item containing fresh cilantro in the 2-14 days before they became ill.
Preliminary FDA and Texas state traceback investigations indicates that cilantro suppliers in Puebla, Mexico were a source of the product that was served at the four restaurants.
The Texas Department of State Health Services said that while no samples of cilantro have been found to be contaminated with Cyclospora, there is enough evidence to establish a strong epidemiological link.
Mexican cilantro was found to be the source of around 250 illnesses in Texas last year .
Although it is believed the outbreak in Texas has ended, illnesses in other states are being investigated.
The Centers for Disease Control and Prevention (CDC) said it had been notified of 304 ill persons with confirmed infection in 2014.
Cases were reported from Arkansas, California, Connecticut, Florida, Illinois, Maryland, Maine, Massachusetts, Michigan, Minnesota, Montana, Nebraska, Pennsylvania, New Jersey, New York (including New York City), Texas, Virginia, Wisconsin, and Washington.
It added that there is no evidence to suggest that any illnesses outside of Texas are linked to cilantro from Puebla, Mexico and investigations are ongoing in other states.
Among 204 persons with available information, ill persons range in age from three to 88 years, with a median age of 49 and 115 (56%) are female.
Reported cases of cyclosporiasis in Texas have returned to baseline levels in August so it is likely that the outbreak has ended.
Cyclospora is acquired by people ingesting something - such as food or water - that was contaminated with the parasite.
Cyclospora cayetanensis is a single-celled parasite that causes an intestinal infection called cyclosporiasis.