Most cases of empyema are caused by pneumococcal, staphylococcal aerob
ic gram-negative, or anaerobic pathogens that gain access to pleural c
avities during pneumonia, thoracic surgery, or trauma. The elderly and
debilitated are at greatest risk. Mast infected pleural collections e
volve through exudative, fibrinopurulent, and organizational stages, e
ach having its own characteristics. Exudative stage parapneumonic effu
sion commonly resolves with antimicrobial therapy alone, whereas fibri
nopurulent parapneumonic effusion invariably requires drainage in addi
tion to use of antibiotics. In the final, organizational stage, surgic
al intervention is almost always necessary for successful eradication
of infection.