Don’t think so. First of all, if you consider catching a cold a minor effect, then it wouldn’t matter if you caught it via a sneeze or through contact. Second, carrying a handkerchief to open doors and such when you’re sick is not all that onerous. I could easily see liability placed for not taking a simple precaution like covering your hands if an uncovered sneeze has already been determined to be negligent.
I agree that it’s silly, but the point was that if you somehow got past the absurdity of holding one liable for one type of transmission of a relatively benign sickness, you’d set yourself up for liability for other types of preventable transmission, i.e., stay home from work if you know you’re sick, or take responsibility for transmitting your sickness. The slope may not start out slippery, but you know how greasy the law can be.