Viral illnesses are the most common cause of upper
respiratory symptoms. Symptoms of a viral illness often appear over several
hours without prior illness. Common viral illnesses include colds and the flu
Bacterial respiratory tract infections are less
common than viral infections. Bacterial infections may develop after a viral
illness such as a cold or the flu. Bacterial infections may affect the upper or
lower respiratory system, and symptoms tend to localize to one area.
The most common sites of bacterial infections in the upper respiratory
system are the sinuses and throat.
Pneumonia is the most common bacterial infection of
the lower respiratory system.
Antibiotics are effective against
bacterial infections only after they have developed, so most doctors do not prescribe them until a bacterial infection is suspected or