Viruses are highly infectious and can be extremely persistent, surviving a long time in the environment. For example, influenza virus can survive for several weeks in the environment. Other infectious viruses such as SARS and RSV are less resilient but may still survive for up to several days in the air or on surfaces.
Probably the most common viral infections in humans are those of the nose, throat, and airways. These infections include sore throat, sinusitis, the common cold, and influenza. These diseases are often termed upper respiratory infections (URIs). In small children, viruses also commonly cause croup and inflammation of the windpipe (laryngitis) or other airways deeper inside the lungs (bronchiolitis, bronchitis).