African Swine Fever in a commercial pig farm: Outbreak investigation and an approach for identifying the source of infection.

African Swine Fever (ASF) is a contagious disease of domestic and wild pigs caused by the African Swine Fever Virus (ASFV). The disease has spread globally in recent years with serious economic consequences to pork production. This report describes an ASF outbreak that occurred in a large-scale Chinese commercial pig farm. The outbreak started in 2018 and presents the spatial and temporal spread of infection in an intensive pig farm. Pig houses adjacent to exit rooms had a higher risk of infection (Odds ratio = 14.4, 95%CI: 1.5-140). Introduction of disease is presumed to have occurred through a contaminated vehicle used in the sale of pigs with poor productivity. This investigation shows the process of ASFV infection and spread in a facility with presumed adequate biosecurity measures. These findings may benefit others in the control of ASF in large-scale pig farms.