Gamer has been removed
This is part of the Operation Broken Eagle DLC.
Early in the DLC campaign, you will reach a helicopter. Pick up the larvae bioweapon container on the ground. This will cause the safe house infecting tutorial to be triggered. It pretty well can't be missed.
Note: All of these achievements in this DLC need to be completed prior to going to the Mayor's Mansion. After that point, you will not be able to obtain these achievements and you will be required to start a new campaign to do so.