Even with a growing body of research on microorganisms and humans in indoor environments, many of their interconnections remain unknown, says a new report by the National Academies of Sciences, Engineering, and Medicine. The report proposes a research agenda to gain a more comprehensive understanding of the formation, dynamics, and functions of indoor microbiomes that can guide improvements to current and future buildings as well as enhance human health and well-being.

The indoor environments described in the report are spaces such as homes, offices, and schools -- the places where people spend most of their time. Microbiomes found in these built environments comprise viruses, bacteria, and fungi that enter a building through its air and water system, are found on pets, plants, and rodents, and is in dirt that is tracked indoors. These microorganisms also live on human skin and in the digestive tract and are shed into the indoor environment.

Available evidence shows that the relationship between indoor microbiomes and human health is complex with effects ranging from harmful to beneficial to neutral. For example, while certain microbes found in damp or water-damaged buildings are associated with respiratory problems, studies also show that children exposed to some microbes early in life are less likely to develop wheezing or allergic disease. The report says in-depth human studies and laboratory animal-model investigations can help improve understanding of the association between exposure to microbes found in indoor spaces and diverse health impacts.

A multidisciplinary research program is necessary to make progress toward understanding and predicting the interactions between microbiomes found in indoor environments and humans, including how such associations change with interventions that affect the physical and chemical characteristics of buildings, the report says. The program will require integrating expertise from multiple scientific, health, and engineering disciplines, including clinical practitioners and professionals in building design, operation, and maintenance.

Once these associations are better understood, the report says, it will be important to translate the knowledge into practice: actions such as updating guidance, standards, and codes for building design and operation.

"At this time, we do not know enough to manage the microbial communities around us in the indoor environment rationally," said Joan Wennstrom Bennett, Distinguished Professor of Plant Biology and Pathology at Rutgers University and chair of the committee that conducted the study and wrote the report. "However, this is a good time to assess this emerging area of disciplinary integration, explore what has been accomplished through research so far, and identify directions in which the field might go in the future."

Research priorities identified in the report include:

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Characterize relationships among microbial communities and indoor systems

The interactions among indoor microbial communities and indoor environment air, water, and surfaces need further investigation to understand the sources, reservoirs, and transport of such microbes. Studies also should be conducted on human behaviors that influence indoor microbiomes.

Assess influence of exposures to indoor environmental microbes on human health

The relationships and connections between human health and microbial exposures need to be examined by developing studies that collect observational data and use controlled human exposures, animal models, and other approaches to test health-specific hypotheses. The report recommends creating exposure assessment approaches to address how combinations of exposures influence functional responses in different parts of the body -- like the lungs, brain, and gut -- at different stages of life.

Explore other impacts of interventions

In addition to health, understanding the environmental and economic impacts of interventions and the use of energy that change the human exposure to microbes in buildings needs to be improved.

Advance tools and research infrastructure for the field

Tools and methodologies for explaining the identity, abundance, activity, and functions of the microbial communities found in indoor environments, including new computation and mechanistic modeling tools to improve understanding, prediction, and management of microbial dynamics and activities in buildings, require refinement. The development of standards and a data commons is also important to increase access to knowledge and facilitate improved cross-study comparison.