I'm loving all the people who go on about "exposure to risk" yet they seem to have no bloody idea that the human immune system only works when it is exposed to "risk"...
Here's a couple of funny little stories, take them for what you will.
Many years ago I was serving in Belize - a jungle if you ever saw one. Rivers run almost black with sediment and contamination. Standing Orders stated that we may not swim in the Belize River that ran past camp and that if we even fell in it we were to visit the Station Medical Center immediately. We had access to a Gemini, a rope and some water skis and some of the lads would take it out to the lagoon and water ski. One day one of the lads who was quite good decided that he would ski all the way back up the river to camp. He nearly made it but a waterlogged log floating low in the water conspired to deny him his glory. He spent 6 days in the medical center violently sick.
A cut of the same river runs right through the center of Belize City. As it passes through, (or hopefully not nowadays), it would pick up the raw sewage of the city as it went. Quite close to the lagoon and right next to the City Market it runs under what was known as "The Swing Bridge", I don't recall if it ever "swung", but it was a commonly used bus stop for lads coming from camp to town and thus attracted the local urchins. For those of you that have traveled to third world countries you know about "urchins" the world over. They see white people - they see money and, the world over, they have their method to extract it from us. In downtown Belize City the schtick was to have you throw a quarter into the filthy black water for them to retrieve... They're amazing, they come up after 30 seconds or more with the quarter every time. I never saw one throw up or look sick... Ever...
Funny how they react utterly differently to another human isn't it? The only logical and sensible explanation is that their body has learned to protect them from the pathogens from it's exposure to them.
I can relate numerous examples of the foolishness of over-protecting and over-medicating everything but, if you haven't got the gist yet then you, ("you" as in any individual reading this), really never will...