There are 12 Trophies that can be collected.

Bronze

First Machete quick kill
Perform your first Quick machete kill while being bullied

Machete quick kill, the third
Perform 3 Machete quick kills while being bullied

My first rescue
Help or rescue your first victim

Elevator repair service
Repair the elevator for the people stuck in High Rise level

Fifth quick kill
Perform 5 Machete quick kills while being bullied

Some tomatoes for her
Provide tomatoes to the hungry lady in Downtown streets level

Three victims helped
Help or rescue 3 victims

Silver

Five victims helped
Help or rescue 5 victims

Ten victims helped
Help or rescue 10 victims

Do it once
Finish the game once(any difficulty mode)

Survivor
Finish game in Survivor mode

Gold

Ultimate rescuer
Rescue / help all victims in the game

http://www.ps3trophies.com/forums/playstation-trophy-news/14215-i-am-alive-trophy-list.html