You will need the following: 1. Medical facility built at your base 2. Upgrade medical facility to the "infirmary" 3. At least one survivor with medical background (a medic is worth their weight in bullets) 4. Medicine When a survivor becomes sick. They are contagious to the other survivors they live with. Your journal will read, "good thing we had an infirmary so we can separate sick people". Lilly is in fact a liar. If a sick survivor stays in your base, the sickness will spread to others regardless of having an established infirmary. The easiest method for containing sickness is to remove the sick survivor from your base. On "Breakdown" you need to switch to the sick individual and run away from your base. About 100 meters away. Switch back to another character. Your journal will then show that the sick survivor is "away from home". Highlight the sick character and have them "check-in". Do not bring them home until they are no longer sick. The survivor is now isolated from the others. Sickness contained. "Story mode" is a little more difficult because you have no "check-in" feature. You can manipulate who will go on a mission. Run your sick survivor away from home (about 100 meters). Switch to all of your remaining characters and keep them home. Monitor your journal for any that try to leave. Even though the sick survivor is sick, they become the only one "away from home". They will take on a mission. Do not do the mission. Allow them to stay away as long as they are sick. Sickness contained. Warning-Warning-Warning: When you use the "check-in" feature on Breakdown the character you have "checked in" becomes vulnerable to attacks. Note their location on your map. Stay away from that ally. If they show up on your mini-map you are to close. Zombies will spawn and attack them at their location. Stay away from them or you will cause their death. This method for containing sickness will lower the meds consumed overall by your survivors.