Pulsed-field gel electrophoresis subtypes of shiga toxin-producing Escherichia coli O157 isolated from ground beef and humans, United States, 2001-2006.

Pulsed-field gel electrophoresis XbaI patterns of Shiga toxin-producing Escherichia coli O157 (STEC O157) isolates (n = 156) found in ground beef sampled from U.S. processing plants and retail stores during 2001 to 2006 were summarized and compared with XbaI patterns from human STEC O157 isolates (n = 14,591) in the national PulseNet E. coli database. Four ground beef samples contained more than one pulsed-field gel electrophoresis subtype of STEC O157. Of the 117 unique patterns found in ground beef, 100 (85%) appeared only once, and 17 (15%) were found in more than one isolate. The six patterns that appeared most frequently in human isolates were also found among the eight most common ground beef patterns. The yearly proportion of human isolates with the two most common patterns changed inversely, such that these patterns traded dominance over the study period. Human isolates with patterns that were first detected in both ground beef and humans contemporaneously were clustered in a 6-month window around the time of the respective ground beef sample. Of the 156 ground beef isolates, 82 (53%) were indistinguishable from at least one human isolate in this 6-month window. The yearly proportions of human STEC O157 isolates that were indistinguishable from ground beef isolates decreased significantly from 2002 to 2003 (12.3-0.8%), and then increased significantly from 2003 to 2006 (overall 0.8-12.6%). This increase in the numbers of human isolates that matched a ground beef isolate occurred during a period of relatively consistent rates of ground beef contamination with STEC O157. Pattern similarity of STEC O157 isolates derived from ground beef and clinical cases may serve as a good predictor of human incidence trends.