There are multiple factors contributing to this situation. I personally think part of the problem is the almost total sanitation of ourselves and our children. I think a lot of effort goes into trying to create a perfectly sterile environment and that's not possible. Every time someone touches the phone, or the doorknob, or the kitchen counter, or multiple other items - there is a rush to sanitize the object with something that will kill 99.9% of all germs. My theory is that by keeping everything in a state of sterilization 24/7 you don't give yourself or your children a chance to build up immunities to various illnesses or other problems that wouldn't be there if they had a little exposure to whatever. That's not to say you should deliberately take your child to a room that's full of kids that have chicken pox or never keep your home clean. It just seems like there's an absolute mania about sterilizing stuff.
I really hate to admit to it, but my ex and I kept our kids away from doctors on religious grounds for about 7 years, and when that "church" crashed and burned over money and sex, I saw my way out and I never looked back. I took my kids to a pediatrician and explained the situation to him. After examining the kids he said I must have been doing something right because he was shocked that the kids were so healthy and in such good shape. I was just letting my children be children and not wringing my hands about every little thing they touched or came into contact with.
This "global" environment that we now have allows people to enter and exit a country or multiple countries with God only knows what kind of illnesses that can be transferred to others. It's no wonder some illnesses or diseases that had been eradicated in this country are now making a comeback.
Rant over.
