On behalf of your co-workers and neighbors, thanks for asking. The rule: If you feel sick, stay home. This is the best way to avoid infecting others, especially since most people are contagious often before symptoms first appear.
As for when you are no longer contagious, the timing varies from person to person. But with the flu, you’re generally safe to be out again 24 hours after your fever breaks, without the help of fever-reducing medicine. And for people who are taking a doctor-prescribed antiviral medication, it’s possible to feel better before the fever breaks, but you should still wait 24 hours after your fever is gone before resuming your normal public activities.
As for the common cold, however, it can be spread while you have symptoms such as a runny nose or cough. So, always cough and sneeze into your sleeve, wash your hands and discard used tissues immediately.