Utility of a Sputum Antigen Detection Test in Pneumococcal Pneumonia and Lower Respiratory Infectious Disease in Adults

<b>Objective</b> To compare the utility of Gram staining, a urinary antigen detection kit and a sputum antigen detection kit were examined for the rapid and early detection of pneumococcal pneumonia and lower respiratory infectious diseases.<br> <b>Methods</b> A newly developed sputum pneumococcal antigen detection kit (RAPIRUN), Gram staining, and urinary antigen detection kit (BinaxNOW) were comparatively evaluated for their ability to detect <i>Streptococcus pneumoniae</i> in patients with pneumonia or lower respiratory tract infection. Sputum culture results were used as a standard for comparison. Furthermore, the pneumococcus-positive rates in culture and rapid tests were compared using polymerase chain reaction (PCR) as a reference.<br> <b>Results</b> Of the 169 patients studied, 54 (32.0%) tested positive for <i>S. pneumoniae</i> in culture. <i>S. pneumoniae</i> detection sensitivities for Gram staining, RAPIRUN, and BinaxNOW were 75.9%, 90.7%, and 53.7%, respectively; thus, RAPIRUN had a significantly higher sensitivity than BinaxNOW (p<0.001). For patients with ≥10⁵ copies/μg of pneumococcal surface protein A DNA PCR analysis, the detection rates of culture, Gram staining, and RAPIRUN were 85.2%, 72.1%, and 82.0%, respectively, however, the detection rate of BinaxNOW was only 47.5%. Comparisons among 45 patients with culture-positive pneumococcal pneumonia revealed that RAPIRUN had a significantly higher detection rate than BinaxNOW in the mild cases (p<0.006), regardless of the number of days from onset (p<0.03).<br> <b>Conclusion</b> RAPIRUN is a rapid testing kit that detects <i>S. pneumoniae</i> in sputum with a high sensitivity and specificity. It is a particularly more useful detection kit than BinaxNOW for early and mild community-acquired pneumonia in pre-treatment patients whose sputum specimens can be obtained.<br>