Taco Bell says the strain of E. coli bacteria that sickened scores of restaurant patrons in New York, New Jersey and Pennsylvania, came from green onions. The Food and Drug Administration says, no it didn't.

Taco Bell identified the green onions as the probable source based on preliminary tests. It discarded the green onions at all 5,800 of its restaurants and on Sunday declared its restaurants were free of the bacteria, which can cause serious illness.

But the FDA says its lab found no E. coli bacteria in the green onion samples supplied to it by Taco Bell. Its scientists say the reported link to scallions was actually a lab error.

That means the source of the bacteria, assuming it is linked to the Mexican fast food chain, remains unknown.

On Friday the FDA said that it was continuing to investigate the possibility that other food items served at the restaurants are the source of the pathogen.

Taco Bell became the focus of the investigation last week after it became clear that most of the more than 60 people who got sick had eaten at one of the chain's restaurants.

Taco Bell temporarily closed 18 stores in New York, New Jersey and Pennsylvania and those that remained open reported a significant drop in business.

Certain not to be helpful for business was an independent report Monday from New York health authorities, who said they found traces of E. coli bacteria in samples of white onion taken from a Taco Bell. However, they said it was not the virulent strain associated with the outbreak, and in fact was mostly harmless.

The Centers for Disease Control and Prevention has confirmed at least 64 cases of illness from the serious strain of E. coli, known as O157.

Infection with E. coli O157 causes diarrhea, often bloody. Although most healthy adults can recover completely within a week, some people can develop hemolytic uremic syndrome, a form of kidney failure.

HUS is most likely to occur in young children and the elderly. The condition can lead to serious kidney damage and even death.