The aim was to identify the causing organisms and assess the association of procalcitonin (PCT) with bacterial pneumonia within 24-hours of intensive care unit admission (ICU-A) among lung transplant (LT) adult recipients.
Secondary analysis from a prospective cohort study. All LT adults admitted to ICU for acute respiratory failure (ARF) over five years were included. Patients were followed until hospital discharge or death.
Fifty-eight consecutive LT patients were enrolled. The most important cause of ICU-A due to ARF was pneumonia 29 (50.0%) followed by acute rejection 3 (5.2%), and bronchiolitis obliterans syndrome exacerbation 3 (5.2%). Microorganisms were isolated from 22/29 cases with pneumonia (75.9%): 17 (77.2%) bacterial, 4 (18.2%) viral, 1 (4.5%) Aspergillus fumigates, with Pseudomonas aeruginosa being the most common cause (45.5%) of pneumonia, with 10 patients presenting chronic colonization by P. aeruginosa. Median [Interquartile range (IQR)] PCT levels within 24-hours after admission were higher in pneumonia (1.5µg/L; IQR:0.3-22.0), than in non-pneumonia cases (0.2µg/L; IQR:0.1-0.7) (p=0.019) and PCT levels within 24-hours helped to discriminate bacterial pneumonia (8.2µg/L; IQR:0.2-43.0) from viral pneumonia and non-pneumonia cases (0.2µg/L; IQR:0.1-0.7). The overall negative predictive value for bacterial pneumonia was 85.1%, increasing to 91.6% among episodes after six months of LT.
Causes of severe pneumonia in LT are changing, with predominant role of P. aeruginosa and respiratory viruses. PCT≤0.5μg/L within 24-hours helps to exclude bacterial pneumonia diagnosis in LT adults requiring ICU-A. A negative PCT test allows antimicrobial de-escalation and requires an alternative diagnostic to bacterial pneumonia.

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