Figure 1.

Factors increasing susceptibility to CAP. (A) Factors present in older adults (starting at the top and moving clockwise): (1) age alone is associated with an increased burden of CAP; (2) the mechanics of ventilation are impaired with age, the thoracic cage is less compliant, the diaphragm is weaker, and microaspiration is common; (3) the lung parenchyma loses elasticity, leading to senile emphysema; (4) the mucociliary escalator is less efficient in older adults, reducing the clearance of bacteria and microparticles from the lung; (5) the lung microbiome alters with age⁸⁴; (6) ageing is associated with a low-grade pulmonary inflammation; (7) multimorbidity and poor nutritional status; (8) polypharmacy are common in old age and CAP; and (9) older adults exhibit reduced responsiveness to hypoxia and hypercapnia.⁸⁵ (B) Factors present in younger children (starting at the top and moving clockwise): (1) younger age is associated with risk of CAP⁸⁶; (2) asthma increases the risk of CAP⁸⁷; (3) previous respiratory infection increases the risk of future CAP⁸⁶; (4) impaired innate immunity; (5) impaired adaptive immunity increases the risk of developing CAP; (6) not being vaccinated against common respiratory pathogens increases the risk of CAP; (7) passive smoking increases the risk of CAP; and (8) environmental pollution increases the risk of CAP in children. CAP, community-acquired pneumonia.