Microbiologic surveillance through subglottic secretion cultures during invasive mechanical ventilation: a prospective observational study

Purpose: Whether subglottic secretions (SS) culture during invasive mechanical ventilation may aid microbiological surveillance is unknown. We conducted a prospective study to assess SS cultures predictivity of endotracheal aspirate (ETA) and bronchoalveolar lavage (BAL) isolates. Materials and methods: 109 patients receiving mechanical ventilation for ≥48 hours underwent SS and ETA surveillance cultures twice weekly; blind BAL was performed in case of clinically suspected pneumonia. Results: SS and ETA cultures were fully concordant in 170 (81%-overall accuracy) of 211 sample pairs. As compared to ETA, SS culture global sensitivity and specificity were 84% [95%CI: 77 to 91] and 74% [95%CI: 66 to 82]; negative and positive predictive values were 82% and 77%. Forty-four episodes of clinically suspected pneumonia were observed. Compared to BAL, SS culture global sensitivity and specificity were 68% [95%CI: 45 to 81] and 63% [95%CI: 44 to 82]; negative and positive predictive values were both 65%. SS sensitivity, specificity, positive and negative predictive values in anticipating BAL isolates were comparable to ETA (all p > 0.20). Conclusions: SS cultures show worthy accuracy in identifying ETA isolates, with excellent sensitivity and good negative predictivity. SS cultures may be not inferior to ETA in predicting BAL results in case of ventilator-associated pneumonia.