Severe community-acquired pneumonia: what's in a name?

Formerly, patients with community-acquired pneumonia admitted to an intensive care unit were considered as having the severe form of the disease. Recently, guidelines have distinguished severe and non-severe community-acquired pneumonia based on clinical definitions. In this review, we describe the different definitions of severe community-acquired pneumonia, and whether a differentiation based on these definitions reflects variation in etiology, risk factors, diagnostic approaches and treatment.

New definitions do not seem to accurately identify patients with high risks of mortality; patients not admitted to an intensive care unit could also be diagnosed as having severe community-acquired pneumonia. Host-factors, such as genetic factors and underlying diseases, can influence severity of presentation of community-acquired pneumonia. Distribution of pathogens in severe and non-severe disease forms is comparable. Initial antibiotic therapy in patients with severe disease should provide coverage of Streptococcus pneumoniae and Legionella pneumophila, as delay is associated with worse outcomes. However, recent studies also suggested an additional benefit of atypical coverage in non-severe disease. As a result, initial therapy with a beta-lactam plus a macrolide or an anti-pneumococcal fluoroquinolone is recommended for all patients with community-acquired pneumonia. Furthermore, the value of vaccination against pneumococci to prevent episodes of severe disease is yet unknown.

As current guidelines do not adequately identify patients with high risk of mortality and intensive care unit admittance, clinical judgment remains important. Based on distribution of pathogens, investigational procedures and therapy recommended in recent guidelines, differentiation between severe and non-severe community-acquired pneumonia does not seem useful. Whether atypical coverage indeed has additional value in non-severe or pneumococcal CAP, however, remains to be determined. In addition, the preventive benefit of influenza and pneumococcal vaccination for development of SCAP awaits further evidence.