Values in this column represent the difference between the populations of E. coli O157:H7 present on romaine lettuce surface before and after treatment with a mean initial population of 7.39 log CFU/g. (Detection limit was 1.7 log CFU/g; if pathogen was not detected by both direct plating and enrichment, the recovery was 0; if the pathogen was only detected by enrichment, the recovery was 1.6 log CFU/g).