What are the chances of contracting a deadly disease in modern america and what should one do to avoid them?

Still 100%: If you don't die of an accident, violence, malnutrition or childbirth, you'll eventually get sick and die. It's the nature of our world. You're less likely to "contract" a fatal infection that will strike you down in health, and much more likely to live until age weakens you or you get cancer, diabetes, or vascular disease. Improve your odds by not smoking and staying physically fit.