E Coli directly competes with Step mutans. It’s interesting, there have been studies that show kids with E. coli in their oral flora get less caries even though they have cariogenic diets. (At least I was told that by a cariologist who has read study after study).

Dietary practices of those other developed countries could explain a difference as well. US has a very cariogenic diet I’m assuming Canada and Australia would be the same.

There could be many factors.

Definitely interesting to observe it at a global level.

These are very quickly thought out considerations so don’t kill me on them lol