Streptococcus pneumoniae in nasopharyngeal secretions of healthy children: comparison of real-time PCR and culture from STGG-transport medium.

Precise methods for the detection of Streptococcus pneumoniae are needed for predicting the consequences of pneumococcal conjugate vaccines on nasopharyngeal carriage. In this study, 400 nasopharyngeal swab samples from children were analyzed using a real-time pneumolysin (ply)-PCR method. The specimens were originally collected into STGG-transport medium and cultured in 1999, after which they were stored at -80 degrees C until analyzed by real-time PCR in 2001. The sensitivities of real-time PCR and culture methods were also studied by analyzing 10-fold dilutions of a pneumococcal broth culture using both methods. Of the 400 nasopharyngeal swab samples, 158 (40%) were positive in culture and 276 (69%) by real-time PCR. A minor part (4%) of the culture-positive samples remained negative by PCR. There was a trend between the quantity of genome equivalents detected by PCR and the number of colonies found in culture. When analyzing 10-fold dilutions of a pneumococcal broth culture, a higher number of genome equivalents were detected using real-time PCR than the number of colonies detected by culture. Quantitative real-time PCR provides feasible means for quantifying pneumococcal carriage. Further studies are needed to confirm that positive PCR findings really indicate the presence of viable pneumococcus in nasopharyngeal specimens.