Brett,
Guangzhou is a dirty infectious place. Maybe Zhanshang is a little more sterile but I doubt it. I think Willy is just lucky or never goes anywhere he can become infected.
After several trips to the hospital to treat ear infections, eye infections, skin infections, dysentery, etc. I learned a few things.
Never eat food from a street vendor or food prepared at the super market.
Wash your hands, ever chance you get. I carried a plastic bag of bleach soaked paper towels.
Never touch your face. Keeping your hands away from you face is a tall order but you will regret it after you held the handrail on the escalator right after someone that wiped their ass with their hand.
Don't tell the hospital that you have insurance. Pay out of pocket and get reimbursed later from the insurance company.