That is pretty quick for them to have caught it. Did they all eat/drink the same thing that day? I don't actually know the soonest one could catch a virus but a few hours seems rather quick. Maybe someone else will know that one.
I think you will be OK tho, I doubt you shared any drinks etc w/ them today and if they are better all ready that is a good sign I'd think. Just take all precautions for a while, which I'm sure you will and also being emet you won't be the one helping any one clean up v* now or ever so if that is what happened you are not at risk.
\"As soon as you trust yourself,you will know how to live.\"
Johann Wolfgang von Goethe
\"Do not anticipate trouble, or worry about what may never happen. Keep in the sunlight.\"
Benjamin Franklin