Why is it harder to determine exposure to airborne transmitted diseases than exposure to bloodborne transmitted diseases?

Blood borne transmitted diseases can be easily traced back to its sources as they need a physical medium to transfer which we can measure, calculate, contain and treat while air borne transmitted diseases lack this feature. The microorganism do not need a physical medium to transfer from one host to another making it difficult to contain the virus. 

the more fit you are, the faster the recovery. your heart rate drops most sharply in the first minute after you stop exercising; it should then fall about 20 beats a minute—a drop of less than 12 beats a minute is considered abnormal. this “recovery heart rate” is measured as part of an exercise stress test.

answer a scar develops;