ID:272382
 
how would i code in a system where if you step on a certain spot you become infected by a virus on something like that.

For example and out of nowhere you get poisoned or something
Look up the procs Entered() and Enter() in the DM Reference.
An example I could give that would probably not apply to your game is a check in a life proc of the world.
world/proc
Life()
for(var/mob/M in world)
if(M.poison)
M.hp --
spawn(10)
world.Life()

turf/poison/Entered(var/atom/movable/a)
if(ismob(a))
var/mob/M = a
M.poison = 1
M<<"You are poisoned!"