Geographic variation in the aetiology, epidemiology and microbiology of bronchiectasis

Abstract

Bronchiectasis is a disease associated with chronic progressive and irreversible dilatation of the bronchi and is characterised by chronic infection and associated inflammation. The prevalence of bronchiectasis is age-related and there is some geographical variation in incidence, prevalence and clinical features. Most bronchiectasis is reported to be idiopathic however post-infectious aetiologies dominate across Asia especially secondary to tuberculosis. Most focus to date has been on the study of airway bacteria, both as colonisers and causes of exacerbations. Modern molecular technologies including next generation sequencing (NGS) have become invaluable tools to identify microorganisms directly from sputum and which are difficult to culture using traditional agar based methods. These have provided important insight into our understanding of emerging pathogens in the airways of people with bronchiectasis and the geographical differences that occur. The contribution of the lung microbiome, its ethnic variation, and subsequent roles in disease progression and response to therapy across geographic regions warrant further investigation. This review summarises the known geographical differences in the aetiology, epidemiology and microbiology of bronchiectasis. Further, we highlight the opportunities offered by emerging molecular technologies such as -omics to further dissect out important ethnic differences in the prognosis and management of bronchiectasis.

Keywords: Aspergillus spp.; Bronchiectasis; Fungi; Microbiome; Mycobiome; Pseudomonas aeruginosa.

Fig. 1

A modern interpretation of Cole’s vicious cycle hypothesis. Abbreviations: NE – Neutrophil elastase, ↑ - Increased

Fig. 2

Predominant aetiologies across different geographic regions and ethnic populations. The individual pie charts indicate the top aetiologies (top 4 or 5) in each cohort. Abbreviations: ABPA – Allergic Broncho-Pulmonary Aspergillosis, COPD – Chronic Obstructive Pulmonary Disorder, NTM – Non-Tuberculosis Mycobacteria, GERD – Gastro-Esophageal Reflux Disease

Fig. 3

Differences in the microbiome between Europe, the US and the Asia-Pacific by sputum culture illustrating the predominant organisms in stable states and viruses only during exacerbations. The bacteriome contributes to host inflammation and disease severity, the virome in exacerbations and the mycobiome is an understudied group with potential clinical impact. Abbreviations: US – United States, UK – United Kingdom, P. aeruginosa – Pseudomonas aeruginosa, NTM – Non-Tuberculosis Mycobacteria, H.influenzae – Haemophilus influenzae, NTHi – Non-typeable Haemophilus influenzae, HTLV-1 – Human T-Lymphotropic Virus type 1, C. albicans – Candida albicans, ABPA – Allergic Broncho-Pulmonary Aspergillosis, CPA – Chronic Pulmonary Aspergillosis, IPA – Invasive Pulmonary Aspergillosis, IA – Invasive Aspergillosis ↑ - Increased, ↓ - Decreased