Microbiological Surveillance Samples in the Diagnosis of Ventilator-Associated Pneumonia

BACKGROUND Ventilator-associated pneumonia (VAP) is a specific subtype of hospital acquired pneumonia (HAP), frequently observed in ICU patients, defined as pneumonia occurred after a minimum of 48 hours undergoing mechanical ventilation (MV). The most recent international VAP treatment guidelines consistently recommend the early administration of empirical antibiotic therapy: however, that often involves the use of two or even three broad-spectrum antibiotic drugs, leading to further selection and proliferation of multi-drug resistant (MDR) bacterial strains. This phenomenon contributes to the worsening of the already significant burden of antibiotic resistant and difficult to treat infections. Several studies have investigated the association between the aetiology of nosocomial pneumonia and underlying microbial colonization, however the correlation between surveillance cultures and those obtained at the time of clinical VAP diagnosis remains inadequately explored. The aim of this study is to analyse the correlation between surveillance samples and the pathogens responsible for VAP, allowing for both targeted early therapeutic intervention and limiting the selection and widespread of MDR bacteria strains. METHODS Outcomes were evaluated in 155 adult patients admitted to our ICU with retrospective assignment of ventilator-associated pneumonia (VAP) diagnosis. Microbiological data regarding bacterial colonization in ETA, rectal swabs, urine samples were retrospectively collected. In the analysis, categorical variables were expressed as absolute numbers and percentages, continuous variables as the median and interquartile range (IQR). For the comparison were performed Chi-squared or Fisher’s exact test for categorical variables, Mann-Whitney U-test for continuous variables. RESULTS Among the 155 patients with ventilator-associated pneumonia (VAP), microbiological identification was achieved in all cases. A microbiological correlation between endotracheal aspirate (ETA) colonization and the VAP causative pathogen was observed in 75.6% of cases when Staphylococcus aureus was involved. Similarly, approximately 50% of patients colonized with Klebsiella pneumoniae or Pseudomonas aeruginosa in ETA developed VAP caused by the same pathogen. Positive rectal swabs for Klebsiella species and Pseudomonas aeruginosa correlated with the same VAP pathogen in 50% and 61.9% of cases, respectively. Furthermore, the present analysis highlighted a notable correlation between urinary tract colonization and the VAP causative pathogen, particularly for Klebsiella species, Pseudomonas aeruginosa, and other Enterobacterales. CONCLUSIONS Despite the retrospective, single-center design, our study suggests that the likelihood of a colonizing pathogen being the causative agent of VAP varies depending on both the site of colonization and the specific pathogen involved. This finding is important to consider when managing and treating patients in the ICU.