http://www.radiologic.theclinics.com/article/S0033-8389(05)00154-5/abstract

Stephen Waite, MD ; Jean Jeudy, MD ; Charles S. White, MD

Pulmonary infections are among the most common causes of morbidity and mortality worldwide, and contribute substantially to annual medical expenditures in the United States. Despite the availability of antimicrobial agents, pneumonia constitutes the sixth most common cause of death and the number one cause of death from infection. Pneumonia can be particularly life-threatening in the elderly, in individuals who have pre-existing heart and lung conditions, in patients who have suppressed or weakened immunity, and in pregnant women. This article discusses some of the important causes of acute lung infections in normal and immunocompromised hosts. Because there often is considerable overlap, infections are categorized by the host immune status that is most likely to be associated with a particular pathogen.