Quantitative detection of Streptococcus pneumoniae from sputum samples with real-time quantitative polymerase chain reaction for etiologic diagnosis of community-acquired pneumonia

We assessed the clinical usefulness of a real-time quantitative polymerase chain reaction (RQ-PCR) method applied on sputum samples to identify Streptococcus pneumoniae in 184 consecutive patients admitted to hospital with community-acquired pneumonia. Induced sputum samples were analyzed by culture and RQ-PCR. In total, 70/184 patients (38%) were diagnosed with S. pneumoniae. Cultures from blood and nasopharyngeal secretions were positive in 27/179 (15%) and 42/158 (27%) cases, respectively. Pneumococcal antigen was detected in 33/169 (20%) urine specimens. In sputum samples, culture was significantly positive in 19/128 (15%), whereas a significant concentration of DNA was found by RQ-PCR in 34/127 (27%) cases (P < 0.001). In 28/34 (82%) patients with RQ-PCR-positive sputum samples, S. pneumoniae was also detected with other methods. In the 34 RQ-PCR-positive sputum samples, 17 were negative by sputum culture, out of which 14 were obtained from patients treated with antibiotics prior to sampling. S. pneumoniae may be rapidly diagnosed by analyzing induced sputum samples by RQ-PCR and may be particularly valuable in patients in whom antibiotic therapy has been initiated.