502 The Most Common Pathogens Isolated From Mechanically Ventilated Burn Patients With and Without Inhalation Injury
Authors: Hori Kaitlin , Shafiee Roxana , Yenikomshian Haig , Newman Dianne , Gillenwater Justin 
Published: May 2023

Abstract

Introduction
The lung microbiota of patients with inhalation injury (INHI) may be distinct from those who do not have INHI. Furthermore, the lung trauma from mechanical ventilation or INHI can increase the risk of ventilator-associated pneumonia (VAP), a leading cause of death in hospital acquired infections. The purpose of this study was to identify the main pathogens isolated from mechanically ventilated patients, with and without INHI, including those that develop VAP to test the hypothesis that INHI itself influences the bacterial present in airways.

Methods
Data was collected via a single institution retrospective review using the Burn Registry and adjacent health records from 1/1/2019 to 12/31/2021. VAP was defined as a hospital-acquired pneumonia that developed ≥ 48 hours of mechanical ventilation and positive culture was growth of any microorganism. Data were examined for the 3 most common pathogens cultured from respiratory samples obtained via bronchoalveolar lavage (BAL), mini-BAL, or sputum induction.

Results
The 3 most common pathogens cultured from respiratory samples are presented as the percentage of the cohort in which each pathogen was identified.
In all mechanically ventilated patients (n=213), Staphylococcus aureus (15.9%), Pseudomonas aeruginosa (9.9%), and Diphtheroid (9.9%) were most commonly isolated. In all patients with INHI (n=78), S. aureus (21.3%), Diphtheroid (13.3%), and gamma hemolytic Streptococcus (10.7%) were the most common. In all patients with no INHI (n=135), S. aureus (14.1%), P. aeruginosa (10.9%) and Diphtheroid (7.0%) were the most common.
In those with INHI and with VAP (n=3), S. aureus (100%) was present in addition to P. aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, and Klebsiella aerogenes which were each in 33% of patients.
In those with INHI and without VAP (n=75), S. aureus (17.3%), Diphtheroid (13.3%), and gamma hemolytic Strep. (10.7%) were the most cultured. P. aeruginosa was in 8% of patients.
In those with no INHI and with VAP (n=7), the most common bacteria were S. aureus (57.1%) followed by Enterobacter cloacae, P. aeruginosa, gamma hemolytic Strep., Diphtheroid, E. coli, A. baumanii, and S. pneumoniae which were each in 28.6% of patients.
In those with no INHI and no VAP (n=128), S. aureus (10.9%), P. aeruginosa (9.4%) were found and alpha hemolytic Strep., Diphtheroid, K. pneumoniae and coagulase negative Staph. were each in 7% of patients.

Conclusions
All VAP patients had polymicrobial infections. Differences in the most common pathogens of ventilated patients with INHI versus those without INHI were seen. P. aeruginosa was not one of the top 3 pathogens in patients with INHI and MRSA was not one of the top 3 pathogens for either group. Follow up studies with a larger VAP sample size are needed to evaluate whether these trends are significant and generalizable.

Applicability of Research to Practice
Understanding the microbiology of patients with and without INHI can guide targeted antibiotic treatment.