Identification of bacterial DNA in noninfectious pleural fluid with a highly sensitive PCR method.

BACKGROUND Bacterial DNA due to bacterial translocation has been identified in noninfectious ascitic fluid samples. OBJECTIVE This study investigated the possible presence of bacterial DNA in the pleural fluid of patients with pleural effusions of noninfectious origin, using a highly sensitive PCR-based method. METHODS Pleural fluid samples from 175 patients (average age ± SD: 69 ± 14 years) with noninfectious pleural effusion (62 transudates, 113 exudates) were analyzed. Bacterial DNA was detected using nested PCR with amplification of a fragment of the gene r16S, with 2 amplification protocols, i.e. low sensitivity (10 and 40 cycles) and high sensitivity (40 and 40 cycles). RESULTS With the less sensitive amplification process, only 1 sample was positive (Haemophilus parainfluenzae in a patient with hepatic hydrothorax). With the highly sensitive nested PCR method, bacterial DNA was identified in the pleural fluid, of both transudative and exudative origin, of 75 of the 175 patients (43%). In cases of isolation of a single bacterium, the more frequent were Escherichia coli, Salmonella enterica and Streptococcus pneumoniae. CONCLUSIONS Regardless of its origin, bacterial DNA can be identified in almost half of noninfectious pleural effusions by using a highly sensitive PCR-based method. The possible clinical significance or prognostic value of these findings deserves to be evaluated.