Summary of the swine farms during sampling.

The criteria for a swine to test positive for influenza A virus was a qPCR Ct value ≤ 37 among the swine oral or nasopharyngeal samples. Data is reported as the average RNA copies/mL of either oral or nasal fluid. All samples were collected during the peak months of influenza A infections. *Room contained 20 sows with 250 piglets. Natural ventilation is not applicable for the sow/nursery farm because the farm is enclosed with solid walls.