Three-dimensional PCA analysis on bacterial data sets subcategorized into 3 major groups: (1) the majority of the IBD samples (in green), (2) samples from patients undergoing colonic surveillance and 2 UC samples with limited viral sequences (in red: ucC03 and ucC04), and (3) outliers of 3 IBD colon samples with relatively higher abundance of human viruses (in blue: cdC05, parvovirus B19; cdC08, CMV and EBV; ucC07, HSV-2 and torque teno virus).