Federal health officials have not determined the source of the outbreak of E. coli illnesses linked to Taco Bell restaurants. Last week, the quick-service restaurant chain pulled green onions from its 5,800 restaurants as a result of preliminary tests that indicated the presence of E. coli. However, subsequent federal testing failed to confirm green onions as the source of the outbreak, officials at the U.S. Food and Drug Administration's Center for Food Safety and Applied Nutrition said yesterday. More than 60 people in five states, mostly in New Jersey, New York and Pennsylvania, have fallen ill with E. coli infections, according to published reports. Meanwhile, more than 30 people have been sickened with symptoms consistent with E. coli infection after eating at a Taco John's restaurant in Cedar Falls, Iowa. The two outbreaks appear to be unrelated, though federal health authorities have not ruled out a connection, published reports said.