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

<b>Background:</b> Protracted bacterial bronchitis (PBB) and bronchiectasis share common clinical and microbiological features, but direct comparative data in children are limited. <b>Objectives:</b> To compare bronchoalveolar lavage (BAL) microbiology between pediatric PBB and bronchiectasis and identify predictors of lower airway and polymicrobial infections. <b>Methods:</b> 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. <b>Results:</b> Among 135 children (85 with PBB, 50 with bronchiectasis), those with bronchiectasis were older (median 7.8 vs. 4.2 years, <i>p</i> < 0.001), while comorbidities showed statistically non-significant differences. The prevalence of lower airway infection was high (PBB 81.2%, bronchiectasis 74.0%; <i>p</i> = 0.330). Pathogen distribution demonstrated statistically non-significant differences between groups after adjustment, with <i>Haemophilus influenzae</i> being the most common pathogen in both groups. <i>Moraxella catarrhalis</i> was more frequent in PBB in unadjusted analysis (21.2% vs. 8.0%; <i>p</i> = 0.045), but this difference did not persist after adjustment. Polymicrobial infection occurred in 25.9% of PBB and 16.0% of bronchiectasis cases (<i>p</i> = 0.180). In regression analyses, younger age independently predicted polymicrobial infection (adjusted OR 0.81, 95% CI 0.69-0.95). <b>Conclusions:</b> 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.