Riddonkulous

I spread through populations fast and wide and find the crowded places where I hide, I travel on the breath the hand the kiss and take what health the unsuspecting miss. I do not choose my host by wealth or name, the young the old the strong receive the same. I force the cities quiet and the borders shut and leave the hospitals beyond their cut. I am the moment nature shows its reach, arriving faster than the cures can teach. What am I