well, that can be complicated. In general,
antibiotics treat infections. Some things like
strep that you treat with antibiotics are contagious and antibiotics work within 48 hours (can be around people, no problem). But in general, lots of things that antibiotics are given for are not contagious such as a sinus infection. That is bacterial in your sinuses--- you can't really give that bacteria to someone. BUT, the reason why most people have sinus infections, bronchitis, etc.