A viral infection is an infection caused by the presence of a virus in the body. 

A respiratory (lung) viral infection refers to a virus that specifically affects the upper (nose, mouth, throat) or lower (deeper within the lungs – trachea, bronchi, bronchioles) respiratory tracts, or both. Viral infections usually happen through the mouth or nose from tiny respiratory droplets produced when someone coughs, sneezes, or talks. 

Upper respiratory tract infections are transmitted through the inhalation of infected droplets of saliva when a sick person sneezes or coughs and the virus travels in the air; or through hand-to-hand contact, when you touch the hand of the infected person and you touch your mouth or nose afterward. 

The viruses in these tiny droplets are generally thought to be contagious if you're within 6 feet of the person who produces them. Viruses in droplets can live on surfaces for several hours, and you can get sick from touching those surfaces. 

Our respiratory system is especially vulnerable to certain viruses that can cause a cold, flu, and other illnesses. 

Anyone can get an upper respiratory infection, though they happen more frequently among children.