Etiology and pathophysiology

The etiology of CAP varies with the age of patients, their risk factors and the geographic location. Nevertheless, S. pneumoniae is the most important causal agent of CAP. Droplet transmission resulting in nasal colonization followed by aspiration is the typical trajectory for disease. Host factors, including cell-mediated immunity, antibody status, and factors that affect these, such as HIV infection, nutrition, and use of immunosuppressive medications, influence the risk of CAP as well as the nature of the pathogens. © 2011 Future Medicine.