Factory:
That is because we are faced with so many mutant strains of infectants. Just because one country treats infections differently than we do does not put both on even ground. Trying to make us more immune by degrading our personal hygiene is not the answer, nor is it a good practice. I'm sure that's not what you would be suggesting.
I'm afraid your logic is faulty. The mutations aren't occurring so rapidly by themselves. The "attacks" we make on them with antibiotics, disinfectants etc. causes them to "defend" themselves by adapting to the new environment just like every other living organism.
Belize isn't "treating infections differently". These people live days by Landrover into the jungle, weeks on foot. But it is a demonstration of how quickly and easily bacteria and viruses can adapt. Depending on which "history" you believe either Fleming discovered penicillin less than 100 years ago or just over 100 years ago if you believe the French doctor was first. So, infections that had remained essentially in stasis for thousands of years, have remained relatively unaltered deep in the jungle yet have ceased to exist in their original form in the modern world. We have superbugs that are immune to the effects of penicillin but the bacteria in the jungle, (that have never been exposed to it), have no defense.
Personal hygiene has little to do with your immune system and less to do with causing the mutation of infection agents. I shower religiously, and like to keep a relatively "clean" household. My intent isn't to kill bacteria but rather to remove the obvious breeding grounds and attractions for their vectors such as mice, rats or cockroaches. Notice that tiny difference? I don't try to kill the infectious entities, I merely don't provide them with somewhere to thrive in my environment.