Breyers Yogurt is being withdrawn from stores in New Jersey, Pennsylvania and Delaware because of cyanide found in a container eaten by a teenager left critically ill Wednesday, authorities said.

Investigators in Camden County, however, called Tuesday's incident an isolated case of tampering because tests on more than 100 similar yogurt containers turned up no sign of cyanide, which can be fatal if taken in small doses.Tests by the U.S. Food and Drug Administration in Philadelphia confirmed the presence of cyanide in the container of Breyers yogurt late Tuesday. Federal officials informed the state Health Department.

Thomas Lee, 17, of Haddonfield, was in critical condition early Wednesday, said Florence Rowe, a nursing supervisor at West Jersey Health System's eastern division in Voorhees. There were no other reports of illnesses.

The cyanide was found in an 8-ounce container of Breyers black cherry yogurt with the code date Feb. 9, 1989. Officials say the yogurt was purchased Jan. 1 at an Acme supermarket in Westmont.