Pass-through events must be defined as part of surface contacts For efficiency, EpiFlex eliminates pass-through infection events from being modeled: for example, an infected A shakes the hand of a non-infected B, who then shakes the hand of another non-infected C, but B washes hands and does not become infected while C does. Therefore, the model definition must account for this through "Surface to hand to mucosa" contacts, where a person can also be a surface.