Hiya all,
sorry not been online much - just got a job (no more surfing all day)
Anyway,
In ME illness is caused by an imbalance in the 4 humours. One of the sources of illness is "bad air" from sewage, rotting corpses etc. (I saw it somewhere in C&G)
So, if I cast Stench of the Twenty corpses in a room, does everyone in the room have to roll to see if they become ill from the bad odour? If so, it's a pretty nasty spell for it's low-level.
I'd say in general no. Although I could certainly imagine a character that had some kind of flaw that made him unusually susceptible.
However, it might also depend on the length of exposure. If a character was exposed to something like Stench of the Twenty Corpses for a significant fraction of the year (like several months), then I think that would count as "unhealthy location" for the purposes of that year's Aging roll.
But normally you want the PeCo guidelines for Hermetic effects to cause disease. If you want a disease carried via the air you could presumably add Au requisites to such PeCo spells.