The viruses that cause the stomach flu are very contagious because they are present in very high amounts in the stool and vomit of ill persons. Another way to catch the stomach flu is by breathing in airborne viruses after an ill person vomits.
Regarding this, how long are you contagious with a viral infection?
Common cold. The common cold is infectious from a few days before your symptoms appear until all of the symptoms are gone. Most people will be infectious for around two weeks. Symptoms are usually worse during the first two to three days and this is when you're most likely to spread the virus.
Are all viral infections contagious?
Infectious diseases are caused by microscopic germs (such as bacteria or viruses) that get into the body and cause problems. Some — but not all — infectious diseases spread directly from one person to another. Contagious diseases (such as the flu, colds, or strep throat) spread from person to person in several ways.