Here is the full list of all 13 Scourge: Outbreak trophies - there are 1 bronze, 11 gold and 1 platinum.
Unlock all available trophies
Obtain all the Unlockables
Obtain Rank 10 in all 4 categories
Obtain Rank 5 in all 4 categories
Complete all 4 Levels in 'Nightmare' difficulty mode
Complete all 4 Levels in 'Normal' difficulty mode
Complete Level 4 in any difficulty mode
Complete Level 3 in any difficulty mode
Complete any Level, in any difficulty, using only the Piranha
Within a single session, obtain at least 6 Awards in one Multiplayer round or one Campaign level.
Complete Level 2 in any difficulty mode
Complete any Level, in any difficulty, in a 4-player co-op game
Complete Level 1 in any difficulty mode