It depends on which virus is causing the cold, and there are lots – including rhinoviruses, adenoviruses and coronaviruses, to name a few, said Dr. Lindsey Baden, an infectious disease specialist at Brigham and Women’s Hospital.
Typically, you are most likely to spread the virus to other people from just before symptoms appear and through the first few days of an illness, when symptoms such as coughing and sneezing, and nasal mucus production, are highest.
Dr. Jack Gwaltney, professor emeritus of internal medicine at the University of Virginia School of Medicine has done research that shows the virus starts reproducing within half an hour of entering the nose; it takes only 8 to 12 hours for new virus to appear in nasal mucus. This rapid production of virus lasts about three days – the days when you are most contagious – and then falls off as the immune system gears up and finally begins to kill the virus. One study showed that when one spouse is experimentally infected with a virus, the other spouse typically gets infected within the first three days.
Since it’s mucus from the nose that is the main carrier of viruses, you should dispose of tissues yourself. It also pays to wash your hands, whether you’re the one who’s sick or the one trying not to become the next victim.
Once you start feeling better, the virus may still be present in your nose for as long as two weeks. But you are much less contagious. As for antibiotics, they don’t do anything for viruses. But if your “cold” is actually a bacterial infection, antibiotics will help with that and will make you less contagious while you are taking them.