This is an expansion for the base game 5150.

From the publisher's website:

Infestation introduces the “tactical role-playing game” side of 5150. Players can use Infestation to “flesh out” their characters, giving them an almost life-like feel. Infestation blends the traditional RPG with fast and easy to follow combat on a personal level. Combining these two aspects allows players to enjoy the cinematic aspect of role-playing while keeping the excitement of a miniatures wargame.

Infestation covers...

1. Fast movement
2. Firing while fast moving
3. The H'DAN CORPORATION flash-bang grenade
4. New grenade throwing procedures
5. Explosions in confined spaces
6. Delayed explosions
7. New ranged combat chart
8. Specific hit locations and damage
9. Cover handled in a different way
10. Variable damage to figures
11. New melee system
12. Man Down check
13. Computers and hacking
14. New equipment
15. Encumbrance
16. Psionics with new QRS
17. "Half Deads"
18. Complete scenario that introduces new movement system
19. New "in encounter" encounter system
20. New variable time clock for encounters
21. Covert Operations Group with new QRS
22. Covert operations
23. Security robot - with new QRS HAFER-2 Security Bot
24. Xeogs are refreshed to use in the scenario if needed - with QRS
25. New way to play solitaire or same side two new aliens with QRS