Antigen detection in the diagnosis and in the prognostic assessment of bacterial pneumonias.

Sputum cultures are not helpful in the immediate management of patients with bacterial pneumonia. Sputum Gram stains may provide a presumptive identification of an etiologic agent; this procedure, however, is insensitive (approximately 50%). Consequently, during the last decade, other more sensitive and specific methods of providing a rapid etiologic diagnosis have been sought. This article discusses data on antigen detection in various body fluids by counterimmunoelectrophoresis and agglutination tests. Results from our own laboratory as well as those reported in the literature are presented. The best estimates of antigen detection rates, by the most sensitive assays, in pneumococcal pneumonia, are as follows: serum, 45%-80%; urine, 50%-64%; and sputum, 75%-100%. There is less information for Haemophilus, Klebsiella, and Pseudomonas pneumonias, but the diagnostic yield is approximately 50%-100%. Data will also be presented on the association between free and complexed antigens and morbidity and mortality in pneumococcal pneumonia. Indicators of morbidity discussed include disseminated intravascular coagulation, duration and severity of illness, and occurrence of nephritis.