Nasal irrigation as an alternate method to monitor airway microbiology in cystic fibrosis.

Background: The sinus cavity may be an alternative sampling site for microbial pathogens in people with cystic fibrosis. However, the congruence between sinus and cough-based sputum sampling is unknown. This study aimed to determine the diagnostic accuracy of nasal irrigation sampling to detect microbial pathogens present in the lower airway.

Methods: People with CF (pwCF) suspected of having chronic rhinosinusitis (CRS) provided an expectorated sputum and a nasal irrigation sample on the same day. Sensitivity and specificity with 95 % confidence intervals were calculated, using the expectorated sputum sample as the reference sample. A non-parametric test of equivalence was used to assess non-inferiority of the nasal irrigation procedure to the standard cough method.

Results: 103 paired samples were collected. Nasal irrigation had a sensitivity and specificity for Pseudomonas aeruginosa of 84 % (95 % CI, 70.9-91.4 %) and 91 % (95 % CI, 80.1-95.6 %), respectively, and for Staphylococcus aureus of 79 % (95 % CI, 61.6-90.2 %) and 85 % (95 % CI, 75.3-91.5 %), respectively. Nasal irrigation demonstrated poor diagnostic accuracy for detecting fungal pathogens [Sensitivity, 0.4 % (95 % CI, 0.08-2.27); Specificity, 99 % (95 % CI, 93.8-99.8)] CONCLUSIONS: Bacterial pathogens common in pwCF can be isolated from nasal irrigation samples, indicating nasal irrigation as a potential alternative diagnostic tool to sputum samples in those suspected of having CRS. Nasal irrigation was not an accurate method to diagnose lower respiratory tract fungal infections. Further research is needed to determine the diagnosis yield of nasal irrigation sampling in pwCF who are asymptomatic for CRS and in a paediatric CF population.