Description of swine sites participating in this study including mean number of animals per site and mean percent of PRRS virus positive farms, stratified by region and system.

Description of swine sites participating in this study including mean number of animals per site and mean percent of PRRS virus positive farms, stratified by region and system.本研究参与生猪养殖场的相关说明：包含各猪场平均存栏动物数量、猪繁殖与呼吸综合征（PRRS）病毒阳性猪场的平均占比，并按区域与养殖体系进行分层统计。