Can you tell that someone has a cold just by standing next to them?

I had this situation when I came to a meeting with a guy with whom I have an instructor-client relationship. I wasn't feeling too good (I had a bit of a stuffy nose and my throat was a bit sore), but IT was nothing too serious, I mean no one at home really noticed. However, this instructor stood next to me and suddenly asked: 'Are you sick?'. This surprised me and I starter wondering whether others can say that somebody is unwell or not?

Can you tell that someone has a cold just by standing next to them?
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