NEW YORK, United States (AFP) — United States (US) officials on Friday pinned the source of a diarrhoea-causing foodborne parasite as shredded iceberg lettuce used by the fast food chain Taco Bell.

A federal investigation by the Food and Drug Administration traced the contamination back to a single supplier of iceberg lettuce from Mexico, which was used by Taco Bell locations in five states, according to a statement from the Centres for Disease Control.

The CDC said that more than 1,644 people in five states — Indiana, Kentucky, Michigan, Ohio and West Virginia — were confirmed to be infected with cyclosporiasis, which can cause “explosive diarrhoea,” among other symptoms.

There have been no deaths and 94 hospitalisations related to that outbreak, the health agency said.

The CDC said that those illnesses were lab-confirmed and linked specifically to the outbreak at Taco Bell locations in those states.

The figure does not encompass all cyclosporiasis infections arising from other causes.

The CDC did not name the supplier, but The Washington Post — citing unnamed sources familiar with the investigation — reported that Taylor Farms, which has production facilities across the country, Canada and Mexico, had sold the lettuce.

Federal officials warned against eating shredded iceberg lettuce from Taco Bell in the impacted five states.

In a statement, Taco Bell said it has “taken immediate action to voluntarily remove potentially impacted lettuce from a supplier in select states.”

“The affected ingredient from our supplier is being indefinitely removed from our supply chain nationwide and will be replaced within 24 hours in select states,” the company added.

“We believe public health is a shared responsibility among restaurants, their suppliers, and authorities, and we are proud to have consistently acted quickly and proactively to protect our guests.”

Untreated, cyclosporiasis could last more than a month. It is generally not life-threatening, but can cause dehydration.

Michigan has been particularly hard hit this year by the parasite, and authorities there have reported more than 5,000 cases.

The FDA cautioned that individual state data often differs from national surveillance numbers as states often include both probable and confirmed cases. There is also a lag between reporting and updating national data.