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.