Are GI infections more common in tourists in India than Africa? If so, why?

A friend asked me “Why do people suffer more from stomach upsets when visiting India vs when going to Africa?”
My response was to question whether this really is the case - there does not seem to be much data other than the odd newspaper article, and then to speculate if it is true, then perhaps it might be down to:
[ul]
[li]Higher population densities in India lead to more human pathogens in the environment and a higher likelihood of infection[/li][li] More developed infrastructure in terms of piped water, sanitation, restaurants etc make visitors less likely to stick to expedition-level cleanliness (sterilise everything, only drink sealed bottled water, etc.) in India compared to Africa [/li][/ul]
However, those are just guesses off the top of my head. What do you grown-ups have to say?