Lower Respiratory Tract Infections (LRTI) are infections that affect the airways (below the level of the larynx), including the trachea and the alveolar sacs.
LRTI are characterized in many different ways. Acute infections that affect the airways include acute bronchitis, bronchiolitis and influenza, whereas acute infections that affect the alveolar sacs can include pneumonia.
Infections are caused by tiny organisms known as bacteria or viruses, which are usually the most common cause. They are carried in tiny droplets and passed between people by coughing, sneezing and at times by indirect contact with surfaces. People who are infected usually produce antibodies to fight the virus. If re-infected, the antibodies help to fight the infection with the same strain. Viruses can change forms and manifest in different strains, causing the body to produce new antibodies. Less frequently, these bacteria can go on to cause a LRTI.