Etiology of Respiratory Infections.

Defects in innate immunity (including neutrophil and complement defects) and humoral immunodeficiency -pyogenic bacteria

cell-mediated immune defects -intracellular microbes such as mycobacteria, herpesviruses and opportunistic infection with Pneumocystis

cigarette smoke compromises mucociliary clearance and pulmonary macrophage activity

Alcohol impairs cough and epiglottic reflexes and also interferes with neutrophil mobilization and chemotaxis

underlying chronic diseases such as CHF, COPD, or diabetes

congenital or acquired immunoglobulin defects (eg AIDS)- ineffective opsonisation of capsulated bacteria( Meningococcus, Pneumococcus and Hemophilus)

decreased splenic function-sickle cell disease, splenectomy- defective killing of capsulated bacteria.