Bacterial Isolates from Bronchoalveolar Lavage in Pediatric Patients with Protracted Bacterial Bronchitis or Bronchiectasis: A Retrospective Comparative Study.

Background: Protracted bacterial bronchitis (PBB) and bronchiectasis share common clinical and microbiological features, but direct comparative data in children are limited. Objectives: To compare bronchoalveolar lavage (BAL) microbiology between pediatric PBB and bronchiectasis and identify predictors of lower airway and polymicrobial infections. Methods: We retrospectively reviewed children diagnosed with PBB or bronchiectasis at a tertiary center (January 2019-June 2025) who underwent both high-resolution computed tomography of the chest and bronchoscopy with BAL within a 6-month period. Multivariable logistic regression was used to identify predictors of lower airway and polymicrobial infections, adjusting for age, gender, tracheomalacia/bronchomalacia, asthma, and Bhalla score. Results: Among 135 children (85 with PBB, 50 with bronchiectasis), those with bronchiectasis were older (median 7.8 vs. 4.2 years, p < 0.001), while comorbidities showed statistically non-significant differences. The prevalence of lower airway infection was high (PBB 81.2%, bronchiectasis 74.0%; p = 0.330). Pathogen distribution demonstrated statistically non-significant differences between groups after adjustment, with Haemophilus influenzae being the most common pathogen in both groups. Moraxella catarrhalis was more frequent in PBB in unadjusted analysis (21.2% vs. 8.0%; p = 0.045), but this difference did not persist after adjustment. Polymicrobial infection occurred in 25.9% of PBB and 16.0% of bronchiectasis cases (p = 0.180). In regression analyses, younger age independently predicted polymicrobial infection (adjusted OR 0.81, 95% CI 0.69-0.95). Conclusions: BAL microbiology showed statistically non-significant differences between PBB and bronchiectasis, supporting the concept of a disease continuum. Younger children were more prone to polymicrobial infection. These findings support early targeted antibiotic therapy and close clinical surveillance to prevent progression to irreversible airway damage.