Saline irrigation via syringe will be administered using a sinus irrigation catheter under endoscopic control.

Patients in the double treatment arm will receive a second photodisinfection treatment 4 weeks following the first treatment with regular follow-up visits

The single-treatment group will receive a single photodisinfection treatment of all involved paranasal sinuses with multiple follow-up visits.

A 0.03% solution of methylene blue is irrigated into the involved paranasal sinus followed by placement of a saline filled balloon with a center light diffusing fiber optic. This is illuminated at 150 mW/cm2 power density for 8 minutes. This is repeated for each involved sinus.

The Sino-Nasal Outcome Test (SNOT-22) has been widely adopted in clinical practice and has been proved to be the most suitable and validated sinonasal outcome scoring system. The SNOT-22 is a disease-specific, quality-of-life-related measure of sinonasal function. Low score indicates good outcome.

Microbiological conventional cultures, gene expression profiling and microbiome profiling by 16s RNA.

This is a 5 item subjective list rated by patients from zero to severe.

This is an endoscopic staging system for non-neoplastic sinonasal disease to evaluate therapeutic outcomes that is complex enough to incorporate the most important measures of the sinonasal cavity but simple enough to facilitate regular clinical use.