A total of 340 porcine stool samples from different aged swine were collected from 17 middle or large-scale porcine farms (200-2,000 sows each) in five provinces of China from April 2008 to October 2009, of which 80 were collected from four farms located in Shanghai, 60 from three farms located in Jiangsu province, 120 from six farms located in Anhui province, 20 from a farm located in Shandong province, and 60 from three farms located in Guizhou province and stored at 280uC (Table 1 ).