Escherichia coli O157 exposure in Wyoming and Seattle: serologic evidence of rural risk.

We tested the hypothesis that rural populations have increased exposure to O157:H7. We measured circulating antibodies against the O157 lipopolysaccharide in rural Wyoming residents and in blood donors from Casper, Wyoming, and Seattle, Washington, by enzyme immunoassay (EIA). EIA readings were compared by analysis of variance and the least squares difference multiple comparison procedure.