Sputum counterimmunoelectrophoresis in the diagnosis of pneumococcal pneumonia.

Fifty-six patients with pneumonia were grouped according to degree of clinical certainty that the etiologic agent was Streptococcus pneumoniae. Of 14 patients with definite or probable pneumococcal pneumonia, 12 had pneumococcal antigens detected in sputum by counterimmunoelectrophoresis (CIE), 13 had a positive sputum culture, and 12 had a Gram-stained smear of sputum suggestive of the diagnosis. Of 9 patients with definite nonpneumococcal pneumonia, none had pneumococcal antigens detected by CIE, but one had pneumococci isolated from sputum culture, and one had a Gram stain of sputum suggestive of pneumococci. Of 34 control patients without pneumonia, five had a positive CIE, 11 had a positive culture, and 15 had a positive Gram stain. When used to differentiate pneumococcal from other types of pneumonia, CIE of sputum appears to be a sensitive and specific test. Among patients without pneumonia, however, CIE lacks specificity. Additionally, sputum Gram stain may correlate as well as CIE with pneumococcal pneumonia, but further substantiation of this observation is necessary.