Correlation of Gram Staining and Quantitative Cultures of Endo- Tracheal Aspirates in Mechanically Ventilated Patients: An Experience from Tertiary Care Hospital

Introduction: Ventilator Associated Pneumonia (VAP) is the most common and fatal nosocomial infection in Intensive Care Units (ICU). VAP is associated with prolonged hospital and ICU stay, high hospital costs, and increased mortality. The accurate diagnosis of VAP causes great difficulty and remains a constant challenge for clinical practice.

Purpose: To determine the effectiveness of gram staining of Endo-Tracheal Aspirates (ETA) and quantitative cultures for predicting VAP and to study the microbiology and susceptibility patterns of MDR isolates.

Methodology: Data was retrieved retrospectively through the records from Jan 1st 2016-July 31st). A total of 865 ETA received from different ICUs were included in the study. Gram staining and quantitative culture results were analyzed. The diagnostic thresholds for ETA quantitative cultures were taken as 105 cfu/ml. Growth below the threshold was assumed to be due to colonization. Diagnostic threshold for gram stain results was assumed as >103.

Results: Out of total 865 samples 464 were sterile, 255 were culture positive and 146 were colonizers and 90 were polymicrobial. Acinetobacter baumannii (44.31%) was found to be the commonest pathogen isolated followed by Klebsiella pneumoniae (23.86), Pseudomonas spp. (11%), Escherichia coli (10.22%). 84.09% of isolates were multi drug resistant. The sensitivity of our study was 75%, specificity 53.42% with a positive predictive value of 70.9%and negative predictive value of 58.90%.

Conclusion: Our study emphasizes that an inevitable oropharyngeal bacterial contamination occurs during the collection of endotracheal aspirates, quantitative culture techniques are always needed to differentiate oropharyngeal contaminants present at low concentration from the infective organisms that are likely to be the cause of pneumonia.