This is part of the Operation Broken Eagle DLC.
After the Eagle Has Landed achievement event, you will learn how to deal with terrorist safe houses. There are 8 total safe houses in the campaign and they are in the same locations as in the main campaign. You will be required to walk up to an exterior vent to use the larvae bioweapon that you picked up from the helicopter crash site. This will turn the safe house icon from green to red.
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.