Microbiology and risk factors for community-acquired pneumonia

The outcome of community-acquired pneumonia (CAP) depends on the interaction between the infectious agent and the host response. Nowadays the etiology of CAP can be established in ~60% of the cases, and Streptococcus pneumoniae remains the main etiological agent in outpatients, those hospitalized, or those requiring intensive care unit (ICU) admission. Recently, the development of nucleic acid amplification techniques has emphasized the role of viruses as important etiological agents in CAP. However, some demographic factors and comorbidities will determine a higher risk of pneumonia. Thus elderly patients or those with toxic habits (smoking, alcohol abuse), and the presence of various comorbidities (respiratory, metabolic, or renal) favor the development of pneumonia by altering the inflammatory response to infection.Some medications like inhaled corticosteroids could play a role in CAP development in chronic obstructive pulmonary disease (COPD) patients. Fortunately some of these risk factors are preventable and modifiable, for example, through smoking cessation and pneumococcal and influenza vaccinations, which are the biggest successes.