You ever look at the sunbeam when it shine through the window and you see all those dust particles suspended in the air? yeah, it's like that. Someone infected breathes out... it lingers for up to 3 hours in the air.. suspended. You sit next the them.. and boom you're infected. .. .but you don't know you're infected because the incubation period is 2-14 days. So you go kiss your grandma..and now she's infected.