DIAGNOSTIC-VALUE OF DIRECT EXAMINATION OF THE PROTECTED SPECIMEN BRUSH IN VENTILATOR-ASSOCIATED PNEUMONIA

Interpretation of the protected specimen brush (PSB) technique is base d on quantitative bacterial cultures (QC), which unfortunately require s at least 24 h. We prospectively compared the diagnostic value of dir ect examination (DE) and QC of PSB specimens in 75 patients with suspe cted pneumonia. We also determined the optimal technique for DE. QC wa s performed using the serial dilution technique. From the original sus pension, two cytospin slides were obtained and stained by the May-Grun wald Giemsa (MGG) and the Gram method for DE. If the prescreening on t he MGG-stained slide was positive, the morphology and the Gram stainin g of the organisms were assessed on the Gram-stained slide. Using the 10(3) colony forming units (cfu.ml(-1)) threshold for defining PSB as positive or negative, DE had a sensitivity of 85% and a specificity of 94%. In a parallel in vitro study, 18 pairs of PSB specimens were col lected from respiratory secretions inoculated with S. aureus. From eac h pah, one brush was processed as described above and the other was sm eared on a glass slide prior to performance of QC. Using direct smear instead of cytocentrifuged preparation, slightly but significantly aff ected QC. Direct examination of cytospin slides is highly predictive o f quantitative bacterial culture results, and provides rapid informati on regarding the Gram-stain morphology of the causative organisms. It may therefore guide initial therapy.