Background: Several predictive models have been proposed to understand the microbial risk factors associated with cystic fibrosis (CF) progression.

Aim: To assess the association between the percent predicted forced expiratory volume in 1 s (ppFEV1) change and the bacteria or fungi identified in the sputum, 107 CF patients from a CF clinic were included and followed up with over five years.

Methods: The relationship between the microorganisms identified in patients' sputum and ppFEV1 course was longitudinally analyzed. An adjusted linear mixed model analysis was performed to evaluate the effect of a transient or chronic bacterial and/or fungal colonization at inclusion on the ppFEV1 change over five years (2017-2021).

Results: We evaluated 107 patients with a mean age of 12.1 years (range 4.2 to 29.5) and a mean FEV1pp 92.6% (range 25, 174) at the first visit. Most patients were colonized with transient Non-Multi-Drug Resistant Pseudomonas Aeruginosa (N-MDR-PA), transient Staphylococcus Aureus (methicillin-susceptible) (MSSA), and Stenotrophomonas Maltophilia. Chronic Multi-Drug Resistant PsA (MDR-PA), chronic Mycobacterium abscessus, and transient S. aureus (methicillin-resistant) (MRSA) were associated with a significant decrease in ppFEV1 (Coefficient ? (95% CI) = -14.54 (-26.83, -2.25); -10.60 (-19.00, -2.19) and -24.78 (-46.96, -2.59), respectively, (p<0.05).

Conclusions: These results confirm recently published data and provide new insights into bacterial colonization as a critical factor for assessing lung function decline in CF patients. Further investigation and larger cohorts are needed.