Diagnosis of pneumococcal pneumonia by antigen detection in sputum.

Pneumococcal polysaccharide was detected by counterimmunoelectrophoresis in the sputum of 20 of 26 (77%) adults with community-acquired pneumonia and a positive sputum culture for Streptococcus pneumoniae. The test was negative in 29 pneumonia patients with negative sputum culture for S. pneumoniae. Pneumococcal antigen was also detected in the sputum of six of nine adults with chronic bronchitis and a positive sputum culture, but was not detected in expectorated respiratory secretions of 22 pneumococcal carriers with colds. Pneumococcal antigen could also be detected in sputum by immunodiffusion; antigen titers varied from 1:2 to 1:256. These results strongly suggest that the detection of pneumococcal antigen in respiratory tract secretions indicates infection caused by S. pneumoniae.