Neutrophilic inflammation in bronchoalveolar lavage (BAL) from children with protracted bacterial bronchitis (PBB) is associated with bacterial biomass but unrelated to alpha diversity and is not driven by single pathogenic species, according to a study published in CHEST.

Collections of BAL were prospectively taken from 28 children with PBB (median age, 1.7 years) and 8 controls (median age, 1.9 years) and cultured using standard measures. Clinically significant cultures were defined as having bacterial density ≥104 colony forming units per mL BAL. Interleukin (IL)-8 was measured using an in-house enzyme-linked immunosorbent assay (ELISA) and IL-1β with a commercial ELISA.

Of all participants in the study, only children with PBB had neutrophilic airway inflammation. Percentage of BAL neutrophil, IL-8, and IL-1β were higher in children with PBB than in the control participants (P <.03). Nearly all (93%) of the children with PBB were culture-positive for ≥1 pathogen, 61% of whom had clinically significant levels. Bacterial biomass of BAL was also significantly higher in children with PBB than in the controls (P =.001) and significantly correlated with neutrophil percentage (rs=0.65; P =.0003). Further, BAL bacterial biomass was significantly higher in specimens that were culture-positive for Haemophilus influenzaeStreptococcus pneumoniae, and/or Moraxella catarrhalis at clinically significant levels (P =.008). BAL microbiota were heterogeneous; cluster analysis from 27 out of 28 children with PBB was partitioned into 4 distinct profiles at 40% similarity threshold.

Potential limitations included a small sample size and incidental but unlikely contamination in the specimens.

The study results suggest that increased bacterial biomass and inflammation in children with PBB cannot be attributed to a single pathogenic species, which is in contrast with previous findings that found lower alpha diversity in children with PBB. A better understanding of the relationships between different PBB microbiota profiles and long-term outcomes is needed to determine whether some children may require more targeted clinical management to prevent recurrent PBB as well as progression to bronchiectasis.

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Disclosures: Multiple authors declare affiliations with the pharmaceutical industry. Please see original reference for a complete list of authors’ disclosures.

Reference

Marsh RL, Smith-Vaughan HC, Chen ACH, et al. Multiple respiratory microbiota profiles are associated with lower airway inflammation in children with protracted bacterial bronchitis [published online January 17, 2019]. CHEST. doi:10.1016/j.chest.2019.01.002