Finding more accurate and rapid strategies for VAP diagnosis
Ventilator-Associated Pneumonia (VAP) remains the most common nosocomial infections in patients admitted to the ICU. VAP diagnosis still relies on a combination of clinical and radiological signs, associated with a quantitative culture of Broncho Alveolar Lavage (BAL) fluid that helps identify pathogens. The inconvenience is that these cultures can postpone the diagnosis by 48–72 hours, a precious time that delays the implementation of an early and more accurate treatment.
The study proposed by Emonet et al  explores the usefulness of metataxonomics and other molecular approaches of Endo Tracheal Aspirates (ETA), in order to detect patients at high risk of developing VAP, and identifying early specific pathogens.
A case-control study was carried out in a prospective single-centre cohort of mechanically ventilated (MV) adult patients, which included 286 MV patients out of 1,154 MV screened patients. From these cohorts, they diagnosed 67 VAP episodes in 62 patients – 40 “definite” and 27 “probable”, although only the first episode for each patient was studied, and each case was matched with at least two controls.
Although no significant changes of ETA or Oro Pharyngeal Secretions (OPS) microbiota between VAP patients and controls were observed at any time point, the researchers did find a VAP discriminatory taxa that could help to diagnose earlier patients likely to develop VAP, in particular a higher quantity of Gram-negative bacteria.
Metataxonomic analyses also showed that a low relative abundance of Bacilli was strongly associated with the development of VAP. Finally, molecular techniques identified the pathogen(s) of VAP found by culture, but also many more bacteria, classically difficult to culture.
STUDY STRENGTHS & LIMITATIONS
The main limitations are the difficulties of getting completely appropriate control matches and the early occurrence of VAP after intubation, which could explain the low frequency of multidrug-resistant organisms.
Metataxonomic analyses alone remain complicated to diagnose VAP in “real life” clinical practice.
Finally, all patients received antibiotics between intubation and day 1 of VAP, making it impossible to analyse the effect of antibiotics on the evolution of respiratory microbiota. However, the high quantity and quality of the extracted samples show a promising research perspective to prevent and treat VAP more accurately.
TAKE HOME MESSAGE
Molecular analyses of respiratory samples showed important taxonomic differences and could help identify the markers of VAP earlier and more accurately.
A multi-focus approach, combining a quantitative PCR-targeting of bacterial markers identified by metataxonomics, and associated with the measurement of the host response, may also be an interesting tool for an early diagnosis of VAP.
This article review was prepared and submitted by Silvia Calvino Gunther from the N&AHP section, on behalf of Journal Review Club.
1) Emonet, V. Lazarevic, C. Leemann Refondini, N. Gaïa, S. Leo, M. Girard, V. Nocquet Boyer, H. Wozniak, L. Després, G. Renzi, K. Mostaguir, E. Dupuis Lozeron, J. Schrenzel and J. Pugin. Identification of respiratory microbiota markers in ventilator-associated pneumonia. Intensive Care Med, , Volume 45, Issue 8, pp 1082–1092.