Until end of turn, creatures you control get +1/+1 and gain trample and infect. (Creatures with infect deal damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Official Rulings for Triumph of the Hordes
6/1/2011 : Multiple instances of infect are redundant.
Others who bought Triumph of the Hordes also bought...