Persistence of pneumococcal antigens in sputum after treatment of pneumonia.

Persistence of pneumococcal capsular antigens (PCA) in sputum was studied by counterimmunoelectrophoresis (CIE) in 36 cases of pneumococcal pneumonia. Antigens were still detected 24 and 48 h after start of antimicrobial treatment, in 92% and 76% respectively of the patients with lobar or multilobar infiltrates. Persistence of PCA was associated with radiologic extension of lung infiltrate. CIE appears to be a valuable diagnostic tool for pneumococcal pneumonia, when treatment has been instituted before admission to the hospital.