Introduction: People living with PCD are frequently acutely infected or chronically colonised by respiratory pathogens. Few studies investigated the effect of these pathogens on lung function, with current management based on evidence from cystic fibrosis.

Aims: We investigated the association between airway microbiology and FEV1 z-scores in PCD patients.

Methods: We collected clinical and microbiology data at baseline from 333 patients aged >5 years from 12 countries. We used Global Lung Function Initiative 2012 references to calculate FEV1 z-scores. We assessed the effect of the 3 most isolated pathogen on lung function by fitting multilevel linear models with country as random effect, adjusted for age at diagnosis, source of microbiological sample, use of antibiotic prophylaxis, presence of respiratory exacerbation, age at lung function, and BMI z-scores.

Results: Most patients were children (n=280, 68.6%). Median FEV1 z-score was -1.72 (IQR -2.74 to -0.65) and varied per country. The most isolated pathogen was H. influenzae (36%, 101 children and 19 adults), followed by methicillin-sensitive S. aureus (MSSA) (15%) and P. aeruginosa (9%, 9 children and 21 adults). Those with a positive culture for P. aeruginosa had significantly lower FEV1 z-scores (? = -0.76, 95%CI -1.30 to -0.21), adjusted for presence of H. influenzae (? = -0.05, 95%CI -0.38 to 0.29), MSSA (? = 0.04, 95%CI -0.40 to 0.48), and other co-variates. Results were similar when restricting analysis to adults.

Conclusions: Our findings suggest P. aeruginosa but not H. Influenzae or MSSA are associated with worse lung function in PCD, regardless of exacerbation status.