Comparison of non-protected lower respiratory tract secretions and protected specimen brush samples in the diagnosis of pneumonia

Abstract

The aim of this prospective study was to compare the results obtained with the non-protected lower respiratory tract secretions samples (LRS) with the protected specimen brushes (PSB) performed through a fiberoptic bronchoscope in mechanically ventilated patients, when pneumonia was suspected. The diagnosis of pneumonia was ultimately made at the end of the hospitalisation, in a double-blind manner by 2 members of the medical staff not aware of the bacteriologic results of LRS and PSB. LRS and PSB were performed in 24 patients. PSB culture was considered as positive at a level of 10(3) colony-forming units per milliliter (cfu/ml) microorganisms. Twenty-five samples from 24 patients were divided as follows: (1) LRS (-) and PSB (-) 5 samples: the clinical diagnosis of pneumonia was never established. (2) LRS (+) and PSB (+) 10 samples: the clinical diagnosis of pneumonia was always established, 2 microorganisms were involved 4 times and 1 microorganism 6 times. (3) LRS (+) and PSB (-) 10 samples: the clinical diagnosis pneumonia was retained in 3 with the possibility of false negative PSB. We conclude that (1) a negative LRS eliminated the diagnosis of pneumonia without PSB; (2) a positive LRS was not sufficient to diagnose pneumonia since PSB was negative in 50% of all LRS (+) cases; (3) the possibility of a false negative PSB must be kept in mind particularly in patients previously treated with antibiotics; (4) 2 microorganisms may be responsible for the pneumonia if the previously determined, as significant, bacteriological count (greater than or equal to 10(3) cfu/ml) appears to be accurate.