About the Study

Humans spend roughly 90 percent of each day indoors in environments built for shelter and environmental control. Recent research has shown that within these built environments there exist a vast number and diversity of species of bacteria, viruses, fungi and protozoa in the air, water, and heating, ventilation, and air conditioning (HVAC) systems, and on surfaces. These constitute dynamic microbial communities or “microbiomes.” The nature, composition, diversity, evolution, and growth of these microbiomes are influenced by interactions with humans, animals and plants, and by factors such as air flow, temperature, humidity, chemical exposures and building materials. These factors are, in turn, shaped by the design, construction, operation, occupation, and use of the built environments.

Although the world of living things is dominated by microbes, very little is known about the vast majority of them. Until recently there have been few systematic efforts to collect and describe the microbes living in or on soil, seawater, freshwater lakes and streams, plants, in the guts and on the bodies of humans and other animals, and in the constructed environments in which we spend most of our time. Our ability to move from identification of genes to a functional understanding of microbial communities and their interaction with ecological conditions remains limited.

Microbial communities in built environments have been shown to affect human health both positively and negatively, influencing our susceptibility to allergies and infectious diseases. The potential health effects from exposure to mold growing in damp environments, for example, are well-recognized. Until relatively recently, most microorganisms in built environments were regarded as pollutants that should be reduced or eliminated from indoor reservoirs. It is now understood, however, that the vast majority of the millions of microbes contained in every glass of water we pour or every breath of air we inhale indoors is non-pathogenic. Many questions remain about the ways in which human occupants shape complex indoor microbiomes and, reciprocally, how the indoor microbiomes to which we are exposed influence the formation and composition of own internal microbiome and what that might mean.

Similarly, “building science” to inform the dynamic between microbiomes and built environments is itself underdeveloped. For example, building materials are poorly characterized in terms of physical structure and chemical composition, factors believed to influence the nature of resident microbial communities and their growth rates. Accordingly, our understanding of how microbial communities respond to changes in building environmental conditions, materials, operation, and maintenance practices is even more limited. We are beginning to understand that microbiomes can have positive and negative effects on the longevity, energy efficiency, and maintenance of the built environments they inhabit, accelerating or decelerating corrosion and degradation of materials, structures, and infrastructural systems. For example, it is estimated that U.S. industries spend $276 billion per year repairing damage to water infrastructure and approximately 50 percent of this cost can be attributed to corrosion influenced by microorganisms. Yet it is believed that the majority of microbes in water systems do no physical harm, and some microbial communities might actually protect pipes from chemical and physical stresses.

A number of investigations are being carried out to better understand microbiomes in buildings such as homes, workplaces, and hospitals, in transit systems, and in unusual environments such as those that support human space exploration. But it is not always obvious which types of complex biological, chemical, and physical data are most important to collect to help answer key research questions, how to design and standardize methods and data interpretation, and which tools from diverse disciplines are available to help address these challenges. For example, information on microbial metabolic activity or factors linked to allergenicity or pathogenicity may be needed to supplement measures of overall composition and diversity such as 16S sequencing. Further discussion may be useful on the types of building data that can be collected and the spatial and temporal resolution that is required from environmental sampling.

Currently, standards pertaining to microbes in the built environment are limited and focus on specific adverse human and material effects or, to some extent, performance. A building’s performance can be measured in terms of its indoor environmental quality (e.g., quality of air, ventilation, lighting, comfort of occupants), its use of materials, energy, and other natural resources, and its emissions into the air and water. In some cases, voluntary consensus and other widely recognized standards have been adopted for the design of mechanical and other building systems (e.g., HVAC systems) or for their performance (e.g., energy efficiency standards). Some infrastructure design takes into account positive chemical reactions, such as oxidation on weathering steel, which develops a “patina” of rust to produce a protective barrier that impedes further access of oxygen and moisture. However, there is, in general, limited knowledge on the complex effects of microbes for in-situ construction materials or design.

Integrating expertise from microbial ecologists, building scientists and engineers, and environmental and public health researchers may help refine the design of studies on microbiomes in diverse built environments, enabling results to more effectively inform our understanding of the indoor habitats in which we spend the majority of our time, how these interactions affect us, and whether we can use the results of such investigations to inform improved design and operation of built environments or to support occupant health and well-being. The question facing us is not whether or not we will shape the microbiomes of built environments, but whether we will do so intentionally and in a manner that is socially responsible, applying new knowledge as it becomes available and as its systemic and health implications are more clearly understood.

The purposes of the proposed study are to assess the current state of knowledge regarding microbiomes of the built environment; identify the scientific, technical, engineering, and health-related knowledge gaps; map out basic and applied research agendas and priorities to guide practical and actionable knowledge to facilitate improving the microbiome/built environment interface; and provide information for government agencies considering whether to include research on the microbiome/built environment interface in their research plans, with the research agenda developed by the study serving as a guide to key issues and questions. The 20-month project will be overseen by an ad hoc committee of approximately 12-14 experts representing various disciplinary and sectoral perspectives.

Statement of Task

The National Academies of Sciences, Engineering and Medicine will convene an ad hoc committee to examine the formation and function of microbial communities, or microbiomes, found in the interior of built environments. It will explore the implications of this knowledge for building design and operations to positively impact sustainability and human health. The committee will:

  • Assess what is currently known about the complex interactions among microbial communities, humans, and built environments, and their relationship to indoor environmental quality. Where knowledge is adequate, summarize implications for built environment design and operations and human health.
  • Articulate opportunities and challenges for the practical application of an improved understanding of indoor microbiomes, with an emphasis on how this knowledge might inform choices about built environment characteristics, both physical and operational, in order to promote sustainability and human health.
  • Identify a seat of critical knowledge gaps and prioritized research goals to accelerate the application of knowledge about built environment microbiomes to improve built environment sustainability and human occupant health.

The committee may discuss and recommend additional actions to advance understanding of microbiome-built environment interactions, including examples of the potential impacts of building and health-related policies and practices, and social or public engagement dimensions.