It depends on what you are sick with.

If you have certain viruses or bacterial infections it is completely possible that they could be carried through sexual fluids. Not to mention the fact that oral sex puts sexual fluids directly into you mouth and near your eyes, it's reasonable to avoid sex if your partner has something you really don't want to catch.

My husband and I will usually still have sex if one of us has a cold (we sleep together, we use the same bathroom, we hold hands all the time, but the time one of us gets sick with a cold, chances are we've already been exposed to the virus) We avoid it if I have a UTI (not because he might catch it, because he wouldn't, but because I feel so awful when I have these) and certainly avoid sex if either of us has a GI bug. Yuck. I adore sex, and we have a lot of sex, but when my tummy isn't right, I don't want it, and he feels the same way if his tummy isn't right.

We had a really bad bout with Influenza (it may have been Pertussis, we're not sure) about 5 year ago. My kids and I were sick as dogs, two of my kids and myself had pneumonia. I didn't feel like sex when it was at it's worse, and then our little one got the pneumonia, and I didn't have time, with three sick kid and a sick me to have sex. But, My Man never caught it.

Sometimes we catch each others' colds, sometimes we don't. But, if your body is invaded with a virus (and most colds, GI infections and all Influenza are viruses) it is reasonable to expect that ANY bodily fluid will carry the virus. Including sexual fluid.

Washing hands before and after sex is always a good idea, but there is still exposure to whatever your partner is sick with.

(I'm a nurse, if that helps any.)

Sorry to say that simply being in the same proximity as a sick person often means sharing their bacteria, viruses, and other microbes. It's actually good for people to be exposed to a variety of different kinds of microbes - it strengthens the population of healthy microbes that protect you against illness! Germophobes don't realize that 9 out of every ten cells in their body are microbial, and without healthy microbes you would die in an instant!

Close proximity, touching, breathing on each other, kissing..for sure!