Researchers analyzed adults from the third wave of the European Community Respiratory Health Survey in Bergen, Norway; Tartu, Estonia; and Melbourne, Australia. Gingival sampling was performed in 355 participants, and metagenomic sequencing was successful for 335 samples. Although the source paper reported slightly different recruited per-center counts in the methods section, the 335-sample analytic population was used in the abstract and results.
Respiratory outcomes included asthma, chronic rhinosinusitis, sensitization status, spirometry, and fractional exhaled nitric oxide. Asthma and chronic rhinosinusitis were defined using questionnaire responses regarding the past 12 months. Chronic rhinosinusitis was defined by symptoms lasting more than 12 weeks, consistent with European Position Paper on Rhinosinusitis and Nasal Polyps criteria.
In adjusted analyses, increasing oral microbiome richness was associated with chronic rhinosinusitis overall. In an online supplemental analysis, the association was strongest among participants with nonallergic chronic rhinosinusitis, while allergic chronic rhinosinusitis was not associated with alpha diversity. Shannon Index showed a similar direction but did not reach statistical significance.
Researchers also observed an unadjusted association between greater richness and forced vital capacity below the lower limit of normal, but the association was attenuated and narrowly missed statistical significance after adjustment. No consistent association was observed between alpha diversity and asthma, forced expiratory volume in 1 second, or fractional exhaled nitric oxide.
The chronic rhinosinusitis subgroup was small, with 33 of 335 participants classified as having chronic rhinosinusitis. Overall, 70 participants had asthma, and 76 had fractional exhaled nitric oxide of at least 25 ppb.
Among 291 bacterial genera detected across the study population, 79 were unique to participants without asthma, 98 were unique to participants without chronic rhinosinusitis, and 54 were unique to participants with fractional exhaled nitric oxide below 25 ppb. No genera were found exclusively among participants with asthma, chronic rhinosinusitis, or elevated fractional exhaled nitric oxide.
In differential abundance analyses using ANCOM-BC2 with multiple-testing correction, 3 genera were more abundant among participants without asthma compared with those with asthma, including an unclassified member of the Lachnospiraceae family. Xanthomonas was more abundant among participants without chronic rhinosinusitis compared with those with chronic rhinosinusitis. However, no genera were more abundant among participants with asthma or chronic rhinosinusitis compared with their respective noncase groups.
Functional gene profiling showed broader differences. Of 10,991 functional genes identified, 2,633 were unique to participants without asthma, 3,391 were unique to participants without chronic rhinosinusitis, and 1,477 were unique to participants with fractional exhaled nitric oxide below 25 ppb. By comparison, 16 functional genes were unique to participants with asthma, 74 were unique to participants with elevated fractional exhaled nitric oxide, and none were unique to participants with chronic rhinosinusitis.
Researchers cautioned that most genera and functional genes unique to outcome or nonoutcome groups were present in fewer than 10% of samples within those groups.
Oral microbiome composition and diversity also differed by study center. Participants from Tartu had higher alpha diversity than participants from Bergen and Melbourne. Beta diversity did not differ by respiratory outcome group but differed significantly across study centers, with center accounting for approximately 7% of variation in microbial composition.
The researchers noted several limitations. The cross-sectional design prevented conclusions about causality or directionality. The cohort was enriched for participants with respiratory symptoms and was not representative of the general population. Recent antibiotic-use data were unavailable, and asthma and chronic rhinosinusitis were based on questionnaire responses, which may have introduced misclassification.
The researchers concluded that increased richness of the oral microbiome was associated with a higher prevalence of nonallergic chronic rhinosinusitis and, to a lesser extent, impaired forced vital capacity and lower sensitization prevalence. They also reported no consistent association between alpha diversity and asthma, regardless of allergic status.
Disclosures: The study was funded by the European Research Council, the Western Norwegian Regional Health Authorities, the Research Council of Norway, and a PhD scholarship from the Graduate School of Health, Aarhus University. One researcher reported investigator-initiated grants for unrelated research from Pfizer, Boehringer Ingelheim, Sanofi, and GlaxoSmithKline; unrelated consultancy for Sanofi; and a speaker’s fee from GlaxoSmithKline. The remaining researchers reported no conflicts of interest.
Source: BMJ Open Respiratory Research