Clinical Significance of Commensal Bacteria Isolated from Bronchoalveolar Lavage of Lung Transplant Recipients

Purpose Allograft infection after lung transplant (LTx) has a significant impact on outcome and has been associated with chronic lung allograft dysfunction (CLAD). Commensal bacteria (CB) are commonly isolated from bronchoalveolar lavages (BAL) in LTx recipients but the clinical significance is unknown. Our objective was to evaluate the association of high growth of CB (≥106 CFU/L) in BAL cultures with subsequent infection or CLAD. Methods We conducted a single-center, retrospective, cohort study of consecutive adult, first bilateral LTx performed 2010-2017. Patients who had no evidence of BAL infection and were alive and CLAD-free throughout the first 6-months post-transplant were included. Infection was defined as the presence of treatment-requiring pathogens in BAL. Outcomes of patients with ≥1CB within the first 6-months post-transplant were compared to patients with no CB isolation episodes within the same time interval. Association of CB with subsequent clinically significant BAL infections using logistic regression models and with time to CLAD was assessed using Cox Proportional Hazards models. Results The study cohort consisted of 202 patients with a median of 7 (IQR 7, 8) bronchoscopies per patient. Seventy of the 202 (34.7%) had subsequent BAL infection at some point post-transplant. Median time to CLAD was 497 days (IQR 131, 1043). Fifty-four (26.7%) patients had at least one episode of CB within the first 6-months post-transplant. In a multivariable analysis accounting for age, sex, primary lung disease, acute rejection score and CMV-mismatch, there was no difference in risk for subsequent infections (OR=0.83, 95% CI 0.40-1.69, P=0.60) or CLAD (HR=0.97, 95% CI 0.50-1.87, P=0.92) between patients with ≥1CB episode versus none. Conclusion We found that in the absence of specific infectious pathogens, isolation of commensal bacteria from BAL of LTx recipients during the first 6-months is not associated with an increased risk of subsequent infections or development of CLAD.