Possible confounders of the relationship between occupational swine contact and Yersinia enterocolitica 0:3 and 0:9 antibodies.

Increased risk of high Yersinia enterocolitica 0:3 and 0:9 antibody content has been previously reported in occupations with swine contact. In this study several possible confounders of this elevated risk among pig farmers and abattoir workers were considered. Only in three instances the standardized risk ratio was decreased close to unity, namely after the standardization of Y. enterocolitica 0:3 IgG antibody positivity for age among abattoir workers, after the standardization of Y. enterocolitica 0:9 IgG antibody positivity for farm butchering among pig farmers and for smoking among abattoir workers. As the decrease did not apply for both pig farmers and abattoir workers and for both 0:3 and 0:9 serotypes considered, it seems reasonable to assume that the three decreases represent products of multiple testing inherent in this kind of search of confounders rather than any true effects. In view of the present knowledge on the determinants of yersinia antibodies in populations, the crude risk ratios for elevated yersinia antibodies can be held to be reasonably unconfounded.