Zombies spawn on standard Peak difficulty or above (and a player can also turn into one if they die with enough spores). When one bites you, you will get a zombie infection which will continuously add spores. To get this achievement, you must use a healing item on yourself that removes spores while the infection is active: a medicinal root, a first aid kit, an antidote, a cure all, or a remedy fungus. Faerie lantern and Pandora's lunchbox should also work.