NEW ASPECTS OF OLD PATHOGENS OF PNEUMONIA

Pneumonia is the sixth leading cause of death in the United States,(18) and it is the infection with the overall highest mortality rate. The mortality rate for patients with pneumonia requiring hospitalization is about 20%, with higher rates for those who require intensive care unit treatment or for those with nursing home-acquired pneumonia.(5,15,38,43,56,61) About half the patients requiring admission to the hospital do not have the cause of pneumonia diagnosed. Three North American studies that used similar definitions to assign a cause for pneumonia are summarized in Table 1. These studies(5, 16, 38) show the relative frequencies with which the various microbial agents cause pneumonia. This article reviews new facets of the ''old pathogens'' of community-acquired pneumonia (CAP). Major changes have occurred in Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes (group A streptococcus), Haemophilus influenzae, and Mycobacterium tuberculosis. For other pathogens, such as Coxiella burnetii, Mycoplasma pnenmoniae, and Pneumocystis carinii, newer aspects of the epidemiology have been recognized.