How could you tell the difference just by looking at a person?

when you say, "harmful to those that dont have proper nutrition, clean environments and are immunologically challenged".
Esp kids when they are babies they all look very beautiful and handsome. I have seen the most sickiest baby who looked as if nothing was wrong (one fo my relatives' child who died of Fever of Unknown origin within few hours).
This is what bothers me the most. Many parents are going to think that their children are safe when there is a real danger and the threat is real!