Negative current output while logic HIGH in IC's?

I've been reading the datasheets for some cmos IC's, particularly 4017 and 4022... I'm wondering, why is it that their current output is negative at logic high, and is small positive when in logic LOW. I see schematics in the net using the 4022 as a led chaser by connecting the base of an npn transistor to the IC's output, but doesn't an npn transistor need positive current at the base to properly bias it?