Table 1.

Risk factors for recurrent pneumonia in children.

Condition	Proposed Underlying Mechanisms
Prematurity/bronchopulmonary dysplasia [19,20]	Inadequate immunity due to low maternal antibodies levels
	Impaired lung function
	Altered innate immunoregulatory response of the lungs to respiratory pathogens secondary to neonatal hyperoxia
Atopy [21,22]	Defective innate immune response of epithelial cells
	Interleukin 13-dependant reduced mucociliary clearance
Tobacco smoke exposure [23,24,25,26]	Neonatal low lung volume and impaired toll-like receptor-mediated immune response
	Suppressed phagocytic activity of neutrophils and monocytes/macrophage cells secondary to reduced production of oxygen radicals
	Increased bacterial adherence
	Impaired lung function
Over-crowding [27]	Increased exposure to respiratory pathogens
Indoor and outdoor pollution [28,29]	Distal bronchial and alveolar inflammation