Fig. 1.

Flowchart of study cohort selection. † For each matched non-sinusitis individual, the same T0 (start of follow-up) as their corresponding sinusitis case was assigned. These selected non-sinusitis individuals were then evaluated using the same exclusion criteria and removed from the list if they met any of these criteria. The matching process continued until each sinusitis case was successfully paired with two non-sinusitis controls. The matching process was conducted without replacement.