Rectal swabs were collected from 304 Bob calves (calves under 10 d old) brought to slaughter in the States of Washington (77 swabs), California (127 swabs), and Wisconsin (100 swabs). The swab samples were tested for the presence of Escherichia coli O157:H7 by the use of a direct smear method, enrichment method, and the use of the Petrifilm Test Kit-HEC-for hemorrhagic E. coli O157:H7 (3M Company, St. Paul, MN). The organism was not isolated from any of the samples by any method, though the 3M test kit did give 21 positive signals. Of these positive signals, three were shown to be caused by sorbitol-positive, O157-positive, H7-negative E. coli. The cause of the other 18 signals was not determined.

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