Devoted South Park fans, namely those who remember "Cherokee Hair Tampons" (2000) and "Sexual Harassment Panda" (1999), know that Kyle is diabetic, most likely a type 1 (like me!), since he's a child and not overweight, and that Stan is asthmatic (like my girlfriend!). But other than these subtle reminders that a couple of our favorite characters aren't exempt from the grim realities surrounding the inherently-flawed human body, I'm far from the only one to state that not one mention is made of either affliction outside these two early episodes.
Keep your friends and family close. They won't be around forever, and they could be gone before you could imagine.