The microbiology of stable bronchiectasis: data from the EMBARC bronchiectasis registry

<b>Introduction:</b> Chronic airway infection is believed to be important in the pathophysiology of bronchiectasis but there have been few large studies of the impact of organisms other than <i>Pseudomonas aeruginosa</i>&nbsp;on clinical phenotypes and outcomes. <b>Methods:</b> Airway samples from patients in the 12 months prior to enrolment in the EMBARC registry were collected while clinically stable. The most prevalent pathogens were identified. Multivariable models were constructed to investigate the impact of pathogens on clinical phenotype and outcomes. Sputum samples in the 12 months after enrolment were used to investigate the stability of airway infection status. <b>Results:</b> 11209 patients had at least one microbiology culture sample taken while clinically stable in the 12 months before baseline. The most frequent pathogens were <i>Pseudomonas aeruginosa</i> (26.0%), <i>Haemophilus influenzae</i> (17.4%), Enterobacteriaceae (9.6%), <i>Staphylococcus aureus</i> (7.0%), <i>Streptococcus pneumoniae</i>&nbsp;(6.7%) and fungi (6.1%), the most frequent of which was <i>Aspergillus fumigatus</i> (2.6%). We confirmed the well described association between <i>P. aeruginosa</i> infection and poor outcomes, but additionally observed significantly increased exacerbations with isolation of <i>M. catharrhalis, S.pneumoniae,</i> enterobacteriaceae and fungi. Isolation of enterobacteriaceae (HR 1.48 (1.06-2.08) and particularly fungi (HR 2.41 (1.82-3.18) were significantly associated with mortality. Persistence of the pathogen during follow up showed wide variation between species (3.3-30%). <b>Conclusions:</b> Gram negative organisms other than <i>P. aeruginosa</i> and fungi are common in stable bronchiectasis and are associated with increased exacerbations and mortality.