The eradication of Aujeszky's disease virus (ADV) in Pennsylvania has suffered because the modes of viral transmission between herds are unknown. Our objective was to identify the major risk factors involved in viral transmission by comparing proportions of operation type, density, quarantine level, and vaccination status of neighboring herds for infected case and uninfected control herds. Multivariate analysis demonstrated an elevated risk of infection with local increases in the proportion of finishing floors. A local increase in the proportion of ADV-quarantined herds was shown to be a significant risk factor, as was an increase in the proportion of vaccinating herds. A reduced risk of infection was found with local increases in the number of feeder pig producer operations.