Gram Stain of Bronchoalveolar Lavage Fluid in the Early Diagnosis of Ventilator-Associated Pneumonia

Abstract

To assess the usefulness of the Gram stain in the early diagnosis of ventilator-associated pneumonia (VAP), we performed 146 protected specimen brushings (PSB) and bronchoalveolar lavages (BAL) in I 18 patients suspected of having nosocomial pneumonia. Gram stain and counts of infected cells were performed in all samples from BAL fluid. A final diagnosis of pneumonia was established in 51 patients and there was no infection in 95 cases. A threshold of 2% of infected cells was used to distinguish between VAP and the group without VAP (sensitivity 86.3%, specificity 78.9%, positive predictive value 68.7% and negative predictive value 91.4%); there was good agreement with the final diagnosis (kappa statistic 0.616; concordance 81.5%). Regarding detection of bacteria using the Gram stain, we found a sensitivity of 90.2%, specificity 73.7%, positive predictive value 64.8% and negative predictive value 93.3%; there was moderate agreement with the final diagnosis (kappa statistic 0.586; concordance 79.4%). In the VAP group, we analysed the degree of qualitative agreement between Gram stain and PSB quantitative cultures: the correlation was complete in 51% (26 of 51 VAP), partial in 39.2% (20 of 51 VAP) and there was no correlation in 9.8% (five of 51 VAP). We conclude that the Gram stain is useful for rapid diagnosis of VAP but unreliable for early adaptation of empiric therapy.