The SARS-CoV-2 transmission riddle - Part 14 close contact

Of transmission and censorship

This was probably the most challenging riddle to write so far. The reason is simple: everyone knows what close contact means, but there are no universal definitions.

Is it a mode of transmission, or is closeness a variable? Does it involve touching someone, or can it include airborne particles emitted from a short distance? If so, what distance: 1, 2, 3 …