Identify the common pathogens causing community-acquired pneumonia.
Identify the risk factors for mortality to improve site-of-care decisions.
Improve antibiotic selection in the empiric therapy of community-acquired pneumonia.
Recognize the risk of avian influenza and community-acquired methicillin-resistant Staphylococcus aureus.
Community-acquired pneumonia (CAP) is a very common condition often leading to hospitalization. Patients admitted to hospital (and the ICU) have a mortality rate that varies from 10% to 30%. Streptococcus pneumoniae is the commonest pathogen independent of the severity of illness. In most clinical settings, atypical organisms (Mycoplasma pneumoniae, Chlamydia pneumonia, and Legionella spp) are the next most common. Only a minority of patients require hospitalization, and several severity-of-illness tools have been developed that can aid in the decision to admit a patient to the hospital. Several tools have been developed to assist in the decision to admit a patient directly to the ICU. Biomarkers such as procalcitonin, C-reactive protein, and cardiac biomarkers are being actively investigated to separate viral from bacterial infections, limit the duration of antibiotic therapy, and serve as prognostic indicators. There is reasonable evidence to suggest that atypical coverage is useful and is associated with reduced mortality and shortened lengths of stays for seriously ill patients. There is considerable concern regarding the emergence of community-associated methicillin-resistant Staphylococcus aureus (MRSA) as a potential pathogen in CAP. As diagnostic tools improve, viral pneumonia is being diagnosed more frequently. Seasonal and pandemic influenza continue to be important clinical issues. There is emerging evidence to suggest that pneumococcal vaccination with a 23-valent polysaccharide vaccine is not particularly helpful, but a new protein conjugate vaccine may be more useful. The diagnosis of pneumonia considerably alters long-term prognosis even after correcting for comorbidities and severity of illness.