Background Studies in developed countries have reported that the prevalence of asthma and rhinitis is higher in urban areas than in rural areas, and this phenomenon is associated with urbanization and changing indoor microbiome exposure. Developing countries such as China have experienced rapid urbanization in past years, but no study has investigated microbiome exposure and urban-rural health effects in these countries. Methods Nine high schools from urban and rural areas were randomly selected in Shanxi Province, China, and classroom vacuum dust was collected for shotgun metagenomic sequencing. A self-administered questionnaire was collected from 1332 students for personal information and health data. Three-level logistic regression was performed between microbial richness/abundance/functional pathways and the occurrence of asthma and rhinitis symptoms. Results Consistent with developed countries, the prevalence of wheeze and rhinitis was higher in urban areas than in rural areas (p < 0.05). Metagenomic profiling revealed 8302 bacterial, 395 archaeal, 744 fungal, 524 protist and 1103 viral species in classroom dust. Actinobacteria (mean relative abundance 49.7%), Gammaproteobacteria (18.4%) and Alphaproteobacteria (10.0%) were the most abundant bacterial classes. The overall microbiome composition was significantly different between urban and rural schools (p = 0.001, Adonis). Species from Betaproteobactera, Gammaproteobacteria and Bacilli were enriched in urban schools, and species from Actinobacteria and Cyanobacteria were enriched in rural schools. Potential pathogens were present in higher abundance in urban schools than in rural schools (p < 0.05). Pseudoalteromonas, Neospora caninum and Microbacterium foliorum were positively associated with the occurrence of wheeze, rhinitis and rhinoconjunctivitis, and Brachybacterium was protectively (negatively) associated with rhinitis (p < 0.01). The abundance of human endocrine and metabolic disease pathways was positively associated with rhinitis (p = 0.008), and butyrate and propionate metabolic genes and pathways were significantly enriched in rural schools (p < 0.005), in line with previous findings that these short-chain fatty acids protect against inflammatory diseases in the human gut. Conclusions We conducted the first indoor microbiome survey in urban/rural environments with shotgun metagenomics, and the results revealed high-resolution microbial taxonomic and functional profiling and potential health effects.

Air transport has become an increasingly important public transport option for many people. The International Air Transport Association estimated a total of 3.8 billion air travelers in 2016, and the number would be doubled in 2035. 1 Compared to typical indoor environments, such as homes and schools, the commercial aircraft cabin is a unique confined environment with low relative humidity (RH) and air pressure. The RH in aircraft is only around 10%, which is much lower than standard indoor recommendation (25%-60%). The cabin pressure is set to an altitude of 1800-3000 m, 2 20% lower than regular indoor environments. Cabin and flight deck have independent ventilation systems and different loads of people, and thus, the environmental characteristics and exposures could also be different between them. There are thousands of commensal and environmental microbes in aircraft, and the aircraft microbiome is associated with passengers' health. The exchanges of microbes occur between human and ambient environments, via contact, skin shedding, and respiratory activities. 3 Previous studies in air transportation have reported the transfer of infectious microorganisms between passengers, such as

Indoor microbial exposure is associated with asthma, but the health effects of indoor metabolites and chemicals are not comprehensively assessed. Here, we collected classroom dust from 24 junior high schools in three geographically distanced areas in Malaysia, including Johor Bahru, Terengganu, and Penang, and conducted culture-independent high-throughput microbiome and untargeted metabolomics/chemical profilings. 1290 students were surveyed for asthma symptoms (wheeze). In each center, we found significant variation in the prevalence of wheeze among schools, which cannot be explained by personal characteristics and air pollutants. Large-scale microbial variations were observed between three centers; the potential protective bacteria were mainly from phylum Actinobacteria in Johor Bahru, Cyanobacteria in Terengganu, and Proteobacteria in Penang. In total, 2633 metabolites and chemicals were characterized. Many metabolites were enriched in low wheeze schools, including plant secondary metabolites flavonoids/isoflavonoids (isoliquiritigenin, formononetin, astragalin), indole and derivatives (indole, serotonin, 1H-indole-3-carboxaldehyde), and others (biotin, chavicol). A neural-network analysis showed that the indole derivatives were co-occurring with the potential protective microbial taxa, including Actinomycetospora, Fischerella and Truepera, suggesting these microorganisms may pose health effects by releasing indole metabolites. A few synthetic chemicals were enriched in high wheeze schools, including pesticide (2(3H)-benzothiazolethione), fragrance (2-aminobenzoic acid, isovaleric acid), detergent and plastic (phthalic acid), and industrial material (4,4-sulfonyldiphenol). This is the first association study between high-throughput indoor chemical profiling and asthma symptoms. The consistent results from three centers indicate that indoor metabolites/chemicals could be a better indicator than indoor microbiome for environmental and health assessments, providing new insights for asthma prediction, prevention, and control.