For example, we found that physicians really don't do a good job being able to distinguish the clinical markers of the rash for chickenpox and smallpox, ... They also had problems with distinguishing a patient's presenting with an attack of botulism from other illnesses.
The risk of spread goes up logarithmically.
The things we read in scary stories are just using our imaginations to evoke a feeling. And sometimes that feeling is happiness or sometimes that feeling is surprise and sometimes that feeling is the spooky scary feelings of Halloween.
We think that's because the clinical marker, specifically the widening of the chest, is something we have all been attuned to since the anthrax attack of 2001.