Hi Geuf
There are many non desructive bacteriums that the body can cope with iff ingested in small numbers, a lot of this depends on the individual to as how much one is infected, what might make someone violently ill might only give another very mild sumtoms, some bacteria can survive the journey through one person then go on to infect the water supply that everyone else is drinking and infect them, this is because of a special coating surounding them, as in Giardiasis, you can never be sure what will happen to all of the people all of the time.
You are correct on the altitude/temp senario here, my survival tips were aimed at those of general use travelling around the world, when I mention polar bear meat earlier, this was for those who knew about the bacteria or lack of it in colder climbs, that lives inside these beasts, if your going to shoot and eat one of these the meat must be almost nuked before eating it.
In many situations you can die from infection due to injury, but one of the fastest and most painful ways to die is from contaminated water, the types of bacteriums found around the world rapidly colonise the gut and dehydration will kill you quickly and faster than many others, Africa is one of the worst places for this, there are hundreds of water borne nasties just waiting for the unwary.
In Africa there are some tiny water borne creatures that can withstand extreme temps, they can lie dormant in the ground for many years, and when accidently collected from an open well and taken in with the water, after the water is boiled and has cooled down again, they can be seen swimming around in the water, it seems that the boiling process reactivates them from their sleep, if you ever get to see this, after the water has been bioled, place some water that others are drinking which hasn't been boiled and see if those little creatures live on afterwards, if they don't, don't drink that water, these little creatures are harmless by the way.
There are some bacteria that can survive boiling temps for several minutes, these are not likely to be present in many water courses, so if your unsure about it, simply boil it while you have the fire going, better to be safe than sorry.
One other fact that some might be interested in is the bacteria called Helicobacter Pylori, this has infected around a quarter of the worlds population, in Japan and other developed countries it is thought to be present in around 40% of the male population over 40, most people can live with it without any symptoms, I myself have had this which did effect me quite badly at one time, you can see all of the information on Google, there is thought that this bactreium has found a way to survive even the most stringent forms of water treatment found in modern society, maybe because of the over use of chemicals and the bacteria becoming imune to them like many modern antibiotics, I beleive that much of this can be avoided by simply boiling the crap out of the beasties, food for thought though.
There is now a simple test for H- Pylori in the form of a ten mminute breath test kit, go check it out on Google.
Davy.