The Clinical Role of the Adenoid Microbiome in the Development of Adenoid Hypertrophy and Otitis Media with Effusion

<b>Background:</b> The adenoid surface serves as a potential bacterial reservoir for upper respiratory tract pathologies, including Adenoid Hypertrophy (AH) and Otitis Media with Effusion (OME). While dysbiosis is implicated in the pathogenesis of these conditions, it remains unclear whether the microbiome of children with otitis media differs significantly from those with simple hypertrophy when compared against a healthy baseline. This study aimed to characterize the adenoid microbiome in children with adenoid hypertrophy with and without middle ear effusion, contrasting them with a healthy control group. <b>Methods:</b> We conducted a cross-sectional case-control study involving 58 pediatric participants divided into three groups: adenoid hypertrophy, adenoid hypertrophy and otitis media with effusion and healthy controls. Nasopharyngeal swabs were collected, and bacterial community composition was analyzed using <i>16S rRNA</i> gene V4 sequencing. Alpha and beta diversity metrics, taxonomic composition, and differential abundance were evaluated. <b>Results:</b> Alpha diversity was significantly reduced in both disease groups compared to healthy controls (<i>p</i> < 0.001), indicating a collapse of microbial richness and evenness. Beta diversity analysis revealed a distinct separation between healthy and diseased cohorts; however, the microbial profiles of the AH and AH with OME groups were nearly identical. Taxonomic analysis demonstrated that disease was characterized by the depletion of health-associated commensals, specifically <i>Veillonella</i>, <i>Actinomyces</i>, and <i>Gemella</i>, and a concomitant expansion of <i>Fusobacterium</i>, <i>Haemophilus</i>, and <i>Streptococcus</i>. <b>Conclusions:</b> Adenoid hypertrophy is associated with a profound dysbiotic shift characterized by the loss of protective commensal flora and the dominance of pathobionts. The lack of significant microbial differentiation between the AH and AH with OME groups suggests that the adenoid surface acts as a centralized reservoir of dysbiosis, the composition of which is conserved regardless of the presence of middle ear effusion. These findings highlight the importance of restoring the commensal microbiome in the management of chronic adenoid disease.