Endotypes of Exacerbation in Bronchiectasis: An Observational Cohort Study.

RATIONALE: Bronchiectasis is characterised by acute exacerbations but the biological mechanisms underlying these events is poorly characterised. Objectives To investigate the inflammatory and microbial characteristics of exacerbations of bronchiectasis.

METHODS: 120 patients with bronchiectasis were enrolled and presented with acute exacerbations within 12 months. Spontaneous sputum samples were obtained during a period of clinical stability and again at exacerbation prior to receipt of antibiotic treatment. A validated rapid PCR assay for bacteria and viruses was used to classify exacerbations as bacterial, viral or both. Sputum inflammatory assessments included label free Liquid chromography/mass spectrometry and measurement of sputum cytokines and neutrophil elastase activity. 16s rRNA sequencing was used to characterise the microbiome.

MEASUREMENTS AND MAIN RESULTS: Bronchiectasis exacerbations showed profound molecular heterogeneity. At least one bacteria was identified in 103 samples (86%) and a high bacterial load (total bacterial load >10(7) copies/g) was observed in 81 patients (68%). Respiratory viruses were identified in 55 (46%) patients with rhinovirus being the most common virus (31%). PCR was more sensitive than culture. No consistent change in the microbiome was observed at exacerbation. Exacerbations were associated with increased neutrophil elastase, proteinase-3, Il-1beta and CXCL8. There markers were particularly associated with bacterial and bacterial+viral exacerbations. Distinct inflammatory and microbiome profiles were seen between different exacerbation subtypes, including bacterial, viral and eosinophilic events in both hypothesis led, and hypothesis-free analysis using integrated microbiome and proteomics, demonstrating 4 subtypes of exacerbation.

CONCLUSION: Bronchiectasis exacerbations are heterogeneous events with contributions from bacteria, viruses and inflammatory dysregulation.