Five of the cases were in western Virginia and 13 of the cases were reported in northeast Tennessee.
Virginia Department of Health spokesman Robert Parker says the agency has found what he described as "similarities" between the strains which have sickened residents in the two states. But Parker says they have not identified a common source.
Earlier this month, a 2-year-old girl from Dryden, Va., died and her brother was rushed to a Tennessee hospital after they became infected with E. coli. Health authorities say the boy was treated and later released.
Health officials from Virginia and Tennessee say they are treating the infections as a possible outbreak.