The best advice that I can give is dont think you're invincible just because you've had your vaccinations.
I spent nearly a month in bed in Peru with typhoid and it was no joke Seriously. I'd had ALL my vaccs about 6 weeks before leaving Ireland.
Having a little bottle of liquid sanitiser for your hands is essential in my view as most toilets in the South American countries dont have soap and toilet paper. Its so easy to pick up germs.
Dont leave your bag on toilet floors - keep it on your back while you're "about your business" as I think this is how I may have picked up the germs.
Dont drink the water. Dont take ice.
If anyone is bold and into taking their Class A's then dont snort them with the local currency - Hepatitis C ( I think) is becoming a big prob in SA because of this.