Microscopic Examination Of Intracellular Organisms In Bronchoalveolar Lavage Fluid For The Diagnosis Of Ventilator-associated Pneumonia:a Prospective Multi-center Study

Background The presence of intracellular organisms (ICOs) in polymorphonuclear leukocytes obtained from bronchoalveolar lavage fluid (BALF) is a possible method for rapid diagnosis of ventilator-associated pneumonia (VAP). However, the validity of this diagnostic method remains controversial and the diagnostic thresholds reported by investigators were different. Our objective was to evaluate the accuracy of quantification of ICOs in BALF for the diagnosis of VAP, and to detect the best cutoff percentage of PMNs containing ICOs (PIC) in the microscopic examination of BALF for the diagnosis of VAP.Methods This was a prospective multi-center study conducted in4ICUs in Wuhan, China, which involving181patients suspected of first episode of VAP. BALF was obtained from all enrolled patients. The BALF samples underwent quantitative culture, cytological and bacteriological analysis to detect the culture results, PIC values and the morphological features of microorganisms. Definite diagnosis of VAP was based on pre-set criteria. The receiver-operating characteristic curve was used to detect the best cutoff point for PIC to diagnose VAP, and the diagnostic accuracy was calculated. Moreover, quantitative culture and Gram's stain of BALF were adopted to diagnose VAP, and their diagnostic accuracy was evaluated as well.Results There were102patients definitely diagnosed with VAP (VAP group), and60patients definitely diagnosed without VAP (no VAP group). We found that ICOs were present in96.08%(98out of102) of VAP patients and20.00%(12out of60) of no VAP patients. The PICs were significantly higher (9.53±6.65%vs0.52±1.33%, P<0.01) in VAP group. In our study, the best cutoff point for PIC to diagnose VAP was1.5%,which had a sensitivity of94.12%,a specificity of88.33%, a positive predictive value (PPV) of93.20%and a negative predictive value (NPV) of89.83%.The area under the receiver-operating characteristic curve was0.956(95%confidence interval,0.925-0.986; P<0.01). When the positive quantitative culture results of BALF were used to diagnose VAP, the sensitivity, specificity, PPV and NPV were65.69%,95.00%,95.71%and61.96%, respectively. Whereas they were70.59%,76.67%,83.72%and60.53%, respectively, when the positive Gram's stain results of BALF were used to diagnose VAP. The concordance between the results of Gram's stain and quantitative cultures was poor, only32.10%(52out of162) was totally right, and17.28%(28out of162) was partially right.Conclusions PIC>1.5%has good diagnostic performance in the microscopic examination of BALF for the diagnosis of VAP. However, Gram's stain is not reliable for the early adaptation of antibiotic therapy, due to the poor bacteriological predictive value.