Respiratory tract infection

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The respiratory tract is the passageway for air between the outer atmosphere and the tiny air sacs of the lungs (alveoli). The tract is divided into:

the upper respiratory tract â€“ nose, throat, voice box (larynx) and upper windpipe (trachea), and
the lower respiratory tract â€“ bronchi (the major branches into which the windpipe divides), bronchioles (smaller branches of the bronchi) and lung substance.

Respiratory tract infections are extremely common, especially those of the upper part of the tract.

Upper respiratory tract infections (URTIs) are usually caused by viruses and are rarely dangerous. They include the common cold, tonsillitis (see Tonsillitis), sore throat (see Sore throat), sinusitis (see Sinusitis), laryngitis (see Laryngitis) and croup (see Croup).

Lower respiratory tract infections (LRTIs) are usually more serious. They affect the breathing tubes (trachea and bronchi) and the lungs, and include acute bronchitis (see Bronchitis), acute bronchiolitis and various kinds of pneumonia (see Pneumonia).