I am of the opinion that it depends on symptoms and severity.
Generally speaking, if it is in my lungs, I have a fever or I have been sick to my stomach I do not work out.
If I feel a little under the weather and I have a little sinus congestion I will work out. Often times under these conditions I feel better after a training session.
These are general guidlines, but this is not a black and white issue. You have feel it out for yourself.
"The fastest way to get strong muscles is also the fastest way to make them bigger. We know what works best to make them strong in the shortest time possible. If you want to get big, do the thing that makes them strong." - Marc Rippetoe
Zdravko Veselin Gaeta
I am not a powerlifter nor am I a bodybuilder. I just want to be big and strong.