"The largest outbreak of highly pathogenic avian influenza (HPAI) virus among commercial poultry farms in the United States, most notably in Minnesota (MN) and Iowa (IA), took place between December 2014 and June 2015. This study addressed potentially contributing environmental factors through a case-control logistic regression analysis in which environmental traits of MN and IA counties were compared to county infection status. Outcomes were: 0=no infected farms and 1=at least one infected farm in terms of turkey (HPAIT); laying hen and pullet (HPAIC); and turkey, laying hen, and pullet (HPAICOMB) farms. The primary exposure was the percent of total county area which is corn grown for grain. To assess if results were influenced by counties with the greatest number of infected farms, one MN county and two IA counties were removed from the datasets. Prior to removal, significant associations were found between the corn variable and HPAIT for MN, corn variable and HPAIT for IA, corn variable and HPAICOMB for MN, and corn variable and HPAICOMB for IA. After removal, regression coefficient estimates remained approximately the same; these counties did not unduly impact the findings. More consideration might be given to the environmental component of the HPAI virus transmission pathway when attempting to predict spread during an outbreak."--Page ii.
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