From Chronic Infection to Microbial Imbalance: Rethinking Chronic Rhinosinusitis

Chronic rhinosinusitis (CRS) has traditionally been viewed as a chronic inflammatory disease in which microbial factors are implicated. However, increasing evidence suggests that CRS may be better understood as a disruption of sinonasal microbial homeostasis rather than as a chronic infection caused by a single pathogen. This review summarizes current knowledge on healthy sinonasal microbiome composition and function as well as microbial alterations in CRS. Particular attention is given to dysbiosis involving potentially pathogenic microorganisms, including Staphylococcus aureus and Pseudomonas aeruginosa, as well as biofilm formation and its interactions with the epithelial barrier and host immune response. We also discuss host-related, therapeutic, hormonal, and environmental factors that may contribute to microbial imbalance. Current evidence does not clearly establish whether dysbiosis is a cause or consequence of chronic inflammation. Based on the evidence synthesized here, we propose that CRS may be understood as a dynamic, bidirectional interaction between microbial imbalance and chronic inflammation, whereby microbial alterations may contribute to epithelial and immune dysregulation, while changes in the host environment influence the sinonasal ecosystem. By integrating these microbiological and host-related perspectives, this review provides a boarder framework for understanding CRS pathophysiology and guiding future research into individual patterns of sinonasal microbial homeostasis.