Creature Abilities
Source Alien Core pg. 208
The following creature abilities are listed here because they are shared by many creatures or are highly complex. The statistics for individual creatures might alter the traits, the number of actions, or other rules of these abilities. Anything noted in a specific creature's stat block overrides the general rules for the ability below. In these abilities, “monster” is used for the creature that has the ability, to differentiate it from any other creatures the ability might affect.
Disease
Source Alien Core pg. 208
When a creature is exposed to a monster's disease, it attempts a Fortitude save or succumbs to the disease. The level of a disease is the level of the monster inflicting the disease. The disease follows the rules for afflictions.