Introduction
The lung is the internal organ most vulnerable to infection and injury from the external environment because of its constant exposure to particles , chemicals and infectious organisms in ambient air . Globally , at least 2 billion people are exposed to the toxic smoke of biomass fuel , typically burned inefficiently in poorly ventilated indoor stoves or fireplaces . One billion people inhale polluted outdoor air , and 1 billion are exposed to tobacco smoke . Although respiratory impairment causes disability and death in all regions of the world and in all social classes , poverty , crowding , environmental exposures and generally poor living conditions increase vulnerability to this large group of disorders .
Respiratory diseases impose an immense worldwide health burden . Five of these diseases are among most common causes of severe illness and death worldwide [ 1 ].
• An estimated 65 million people have moderate to severe chronic obstructive pulmonary disease ( COPD ), from which about 3 million die each year , making it the third leading cause of death worldwide – and the numbers are increasing [ 2 , 3 ].
• About 334 million people suffer from asthma [ 4 ], which is the most common chronic disease of childhood , affecting 14 % of children globally . The prevalence of asthma in children is rising [ 5 ].
• For decades , acute lower respiratory tract infections have been among the top three causes of death and disability among both children and adults . Although the burden is difficult to quantify , it is estimated that lower respiratory tract infection causes nearly 4 million deaths annually and is a leading cause of death among children under 5 years old [ 6 ]. Moreover , acute lower respiratory tract infections in children predispose for chronic respiratory diseases later in life . Respiratory tract infections caused by influenza kill between 250,000 and 500,000 people and cost between US $ 71 and 167 billion annually [ 7 ].
• In 2015 , 10.4 million people developed tuberculosis ( TB ) and 1.4 million people died from it [ 8 ].
• The most common lethal neoplasm in the world is lung cancer , which kills 1.6 million people each year [ 9 ]; and the numbers are growing .
In addition to these five , there are several respiratory disorders whose burden is great but less well quantified .
• More than 100 million people suffer from sleep-disordered breathing [ 2 ].
• Millions live with pulmonary hypertension [ 2 ].
• More than 50 million people struggle with occupational lung diseases .
Respiratory diseases account for more than 10 % of all disability-adjusted life-years ( DALYs ), a metric that estimates the amount of active and productive life lost due to a condition . Respiratory diseases are second only to cardiovascular diseases ( including stroke ) [ 10 ].
Forum of International Respiratory Societies 7