In 2004, 803 rural Iowans from the Agricultural Health Study were enrolled in a 2-year prospective study
of zoonotic influenza transmission. Demographic and occupational exposure data from enrollment, 12-
month, and 24-month follow-up encounters were examined for association with evidence of previous and
incident influenza virus infections. When proportional odds modeling with multivariable adjustment was
used, upon enrollment, swine-exposed participants (odds ratio [OR] 54.9, 95% confidence interval [CI]
13.0–232.6) and their nonswine-exposed spouses (OR 28.2, 95% CI 6.1–130.1) were found to have an
increased odds of elevated antibody level to swine influenza (H1N1) virus compared with 79 nonexposed
University of Iowa personnel. Further evidence of occupational swine influenza virus infections was
observed through self-reported influenza-like illness data, comparisons of enrollment and follow-up serum
samples, and the isolation of a reassortant swine influenza (H1N1) virus from an ill swine farmer. Study
data suggest that swine workers and their nonswine-exposed spouses are at increased risk of zoonotic
influenza virus infections.

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