1) as long as you're in the tourists areas whether you're in Rio, Sampa or Salvador etc, you'll be alright. Don't go to no favelas looking around like you don't live there. You don't go to random projects when you visit Chicago, NY or LA at homeWhat about the crime ?
I've heard stories about tourist getting robbed by gunpoint even murdered.
And don't forget about the reported high prevalence of HIV / AIDS.

2) the US has always had a higher HIV/AIDS rate.