The distribution of lung involvement can also be determined by CT and may be suggestive of aetiology. CF (bilateral) and tuberculosis (often unilateral and upper lobe) typically cause upper lobe involvement; allergic bronchopulmonary aspergillosis causes more proximal bronchial involvement. Middle lobe involvement has been observed in the setting of lymph node enlargement with bronchial obstruction, and is also associated with atypical mycobacterial infection with possible additional radiological findings of peripheral infiltrate and mucus plugging. Lower lobe involvement appears to be a feature in aspiration, ciliary dyskinesia, hypogammaglobulinaemia and childhood respiratory infection, although these findings have not been universal.
Spirometry, including measurement of forced expiratory volume in one second (FEV1), forced vital capacity and bronchodilator responsiveness, should be performed in all patients at diagnosis and repeated in monitoring on an annual basis. A significant increase (greater than 12%) in FEV1 or forced vital capacity after bronchodilator use may be seen in up to 30% of patients tested and may indicate asthma or clinically significant reversible airflow obstruction. These patients should be treated with bronchodilators and, if necessary, low-dose inhaled corticosteroids.
Sputum culture should be performed at diagnosis to ascertain colonisation and to direct subsequent antibiotic therapy. Nontypeable H. influenzae, Streptococcus pneumoniae and Moraxella catarrhalis are the most common isolates identified in children and adults (in about 35% of patients), followed by P. aeruginosa (in about 5 to 30% of patients). Isolates of mycobacteria and Aspergillus species are found in few patients, but when found may adversely impact prognosis and will require specific treatment. The geographical prevalence of specific microbial isolates varies markedly. Studies in Spain and the US have suggested nontuberculous mycobacterial prevalence of between 8.3 and 63%.17,18
Changes in microbial flora over time are a feature of bronchiectasis and surveillance with annual follow up is necessary. Pseudomonas acquisition is a feature of late bronchiectasis and once colonisation has occurred eradication may prove difficult. Sputum cultures are usually adequate for testing but pharyngeal swabs may occasionally be needed in children. Bronchoscopy to obtain specimens for microbiological culture is only rarely required.
P. aeruginosa is a highly evolved Gram-negative bacteria characterised by its use of biofilms and the development of complex antimicrobial resistance mechanisms, making treatment challenging.19 Acquisition of P. aeruginosa is a significant event and is associated with about a threefold increased risk of death, sixfold increase in hospital admissions, doubled rate of exacerbations and poorer quality of life. Additionally, healthcare costs have been shown to increase by 87% in the 12 months after colonisation.20,21 This risk highlights the importance of the active management of patients to minimise cross infection within clinical consulting spaces.22
Standard microbial cultures are selective and identify a limited range of bacterial species in clinical samples. Newer, culture-independent techniques employ molecular approaches such as 16S rRNA gene sequencing to describe the airway microbiome and have been shown to detect a much greater variety of microbes than standard culture techniques.23 Such techniques may become increasingly important as predictors of outcome (and possibly exacerbations) in the airway since it has been recognised that perturbations of microbial interactions within the microbial community of the lung microbiome appear to be affected by disease severity, airway obstruction and exposure to antibiotics.