The source of exposure in a deadly Legionnaires' outbreak on the Upper East Side has been "eliminated," the city's health commissioner, Dr. Alister Martin, said Friday. As of Thursday, seven people had died in connection with the outbreak. "The source of this Legionnaires' disease community cluster has been eliminated," Martin said. "We announce that there is no longer an elevated risk of Legionnaires' disease for the Upper East Side ZIP codes of 10128, 10028 and 10075."