An outbreak of a parasitic stomach illness has infected more than 4,100 people across the United States.

The US Centers for Disease Control and Prevention (CDC) said on Tuesday that 308 people with confirmed cyclosporiasis infection were admitted to hospitals across 41 states, with no deaths reported so far.

Symptoms of cyclosporiasis usually appear a week after exposure to the Cyclospora cayetanensis parasite from eating contaminated food or drinking contaminated water, and include frequent diarrhoea that can last for weeks.

The CDC also cautioned that 7,400 people with suspected infection were under review and the total was likely to rise. Many cases have been linked to lettuce produce.

On July 17, US firm Taylor Farms issued a recall for iceberg lettuce grown in Mexico and exported to US shops and restaurants after US investigators pointed to Mexican facilities as a likely source for the outbreak.

However, Mexican Secretary of Health David Kershenobich disputed the findings, stating on Tuesday that there was no evidence the outbreak began in the central state of Guanajuato, where authorities are investigating.

“So far, no evidence has been found to indicate that it originated there,” he said.

The US Food and Drug Administration has issued conflicting information on the source of the outbreak. (Al Jazeera)