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 (influenza).
Antibiotics are not used to treat viral illnesses and do not
alter the course of viral infections, unless the viral infection is influenza
A and medication is started within the first 24 to 36 hours.
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 ear, the sinuses,
or the 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 health professionals do not prescribe them until
a bacterial infection is suspected or confirmed.