Flu: You can actually infect someone before you start feeling symptoms of the flu. You are most contagious in the 3 to 4 days after you start to feel sick, but you remain contagious as long as you have symptoms. Usually this is about a week, but it could be a few days more for children or people with weak immune systems. Some people can transfer the virus without ever getting symptoms.
COVID-19: This infection can cause fever, chills, trouble breathing, body aches, fatigue, cough, and nausea. But you can spread the virus 2 to 3 days before you notice any of these signs. You can also pass it on to others if you are not showing symptoms. If you are sick, you can be contagious for a while, so stay away from others until your symptoms improve and you have been without a fever for 3 days in a row. If you test positive for the virus but do not have symptoms, it is best to keep away from others for 10 days to see if you get sick.
Chest cold: Sometimes called bronchitis, it happens when regular cold symptoms move down to inflame your lungs, which makes you cough. But whether it is a cold, the flu, or some other virus, the rule of thumb is the same: You are contagious for as long as you have symptoms, and maybe a little bit longer. To stop the spread, keep your hands clean at all times and cover your mouth when you sneeze or cough.