Help! I'm stressed!

Last week someone at work was s*, apparently one of her kids was up all night with it the night before. I'd convinced myself it couldn't be a virus cos she'd caught it too quick from him. Then yesterday I went in, spoke to someone who had been up all Sunday night (but still came in to work for half a day - grrrrrrrrrr) being s*. They said someone else in the office had it last week as well. I've also convinced myself I heard at least 3 other people talking about it, but it's a huge office and I've never any idea of who should or shouldn't be in, so I can't tell how many people have actually been off with it.

I've got to go back in today, plus go and work somewhere else for the rest of the week and I'm really scared I'm going to have caught it. I'd been being less careful recently with the warmer weather and this phobia was starting to feel a bit more under control. Now I'm back to square 1 and I'd really like to stay at home, but I can't.