6

Moving Forward: A Vision for the Future and Research Agenda

Research on the communities of bacteria, viruses, fungi, and other microbes found in built environments illustrates the multiplicity of interactions among indoor microbiomes, their influences on human occupants, and how choices about building design and operation affect microbial communities. Prior chapters in this report have summarized lessons learned from research efforts in this field that extend back decades. Yet, knowledge in many of these areas remains incomplete. How could indoor microbiomes be changed and their impact on occupants be enhanced or reduced if advancing microbial knowledge could be translated into practical application? Since knowledge about the interactions among indoor microbiomes, human occupants, and built environments is not yet at an actionable level, this chapter lays out a vision for the future of buildings informed by microbial understanding and provides a research agenda for making progress toward achieving this vision.

A VISION FOR THE FUTURE OF THE FIELD: MICROBIOME-INFORMED BUILT ENVIRONMENTS

In the committee’s vision for the future, greater understanding of indoor environments will result in buildings that support a more productive, healthier population at lower cost and with reduced impacts on the outdoor environment. This reality could be achieved by harnessing current and future knowledge about the relationships among the built environments, microbial communities, and human occupants and applying it through improved practice.

This vision, which is still far from being a reality, is not to be interpreted as direct recommendations or conclusions. But it is driven by a desire to design, construct, and operate buildings that support occupant health and well-being while promoting sustainability and resilience. The vision also takes into account several trends that will continue to impact building design and operation, including climate change; aging building stock; increasing urbanization; the adaptive reuse of existing buildings; and the increasing use of chemicals indoors, including antibiotics and antimicrobials. Buildings of the future that emphasize sustainability and overall population health will be well positioned in a world that addresses the effects of climate at regionally distinct levels, incorporating a variety of technological changes. These trends affect many of the trade-offs discussed in Chapter 5—for example, the need for buildings that can adapt to changing outdoor conditions; requirements to improve the energy efficiency of buildings; and the advantages and disadvantages of natural, mechanical, and hybrid ventilation systems. As a result, future buildings will reflect attempts to optimize occupant health, energy use, and other features in concert, based on a thorough consideration of public health implications. They will need to accommodate occupant comfort and preferences for individual environmental control (Boerstra, 2016), as well as draw on new technologies that support predictive and adaptive management of building conditions, including reactions to changing outdoor conditions. Future buildings also will need to reflect the economic realities that underpin decision making about building design and operation.

To design these future buildings, a number of challenges will need to be overcome. These are multidimensional challenges that will not be simple to address and that will likely require significant investment and buy-in from both public and private entities. The committee’s vision for the future includes the components detailed below.

Researchers will have a much deeper understanding of the effects of indoor microbial communities on human health, and the connections among exposure, response, and health outcomes will be established. Scientists and practitioners will know how environmental microbial exposures result in physiologic responses linked to significant health impacts and will be able to quantify how these exposures are connected, in turn, to particular physical, chemical, and biological conditions of the built environment. They also will have gained greater understanding of which types of people, in which types of indoor settings, experience adverse or beneficial health effects as a result of particular exposures. Refinements of this understanding will be important for shaping guidance that can have broad application while accounting for the existence of significant individual variability.

The growth, establishment, and evolution of indoor microbiomes will be better understood. Understanding of the behavior and functions

of indoor microbial communities, as well as the factors that affect their proliferation and activities, will improve. Scientists will have a concrete understanding of which building design and operation choices impact indoor microbiome dynamics and how these choices impact microbiomes positively or negatively from a building health and human health perspective.

The sources of microorganisms in buildings that impact human health and well-being positively or negatively will have been identified and understood. Not only will potentially beneficial and harmful microbes present in indoor environments have been identified, but their differential effects on humans of various ages, sexes, and health status will also be understood to inform building engineers and facilities managers about how to operate and maintain buildings to promote the health of their occupants. Once this knowledge base has been achieved, it will be possible to design, construct, operate, and maintain buildings in a manner that will reduce harmful microbes of concern while supporting building sustainability and health goals. For example, design features will be implemented to manage water, airflow, and light so as to allow for an abundance of beneficial microbes and a reduction in microbes with negative impacts. To prevent detrimental microbial effects associated with dampness, future buildings will include features to minimize or mitigate water damage. Many of these features—such as providing accessibility to concealed spaces that may be sources of microbes or employing enclosure assemblies that minimize condensation—are available with today’s technology but are not consistently incorporated into buildings. Similarly, heating, ventilation, and air conditioning (HVAC) systems will be designed with features that reduce condensation and water accumulation, as well as with improved air filtration and reliable outside air ventilation for controlling humidity and indoor pollutants.

Advanced technologies that facilitate indoor environmental quality and energy efficiency will have been developed, installed, and embraced in building operation. Buildings of the future will incorporate improved technologies to support building operation, including sensing and self-actuated maintenance. To this end, detection and response strategies will be required in both unconditioned and occupied spaces, because the former spaces can have very different environmental conditions and microbial communities but still be well connected to occupied spaces. Specific examples include the incorporation of sensors to detect water penetration, coupled with new or modified materials capable of self-sealing to minimize leaks. Sensors for and responses to the performance of air and water filtration, occupant density, and indoor and outdoor air and water quality, or sensors to identify situations in which outdoor air is more healthful than indoor air, coupled with automatic controls to change airflow to optimize indoor environmental quality, will also be important. Finally, sensors that sample air, water, dust,

and other media to determine concentrations of potentially beneficial and potentially harmful microbes will allow improved control of the environment. Many of these sensors may already exist but are not being deployed routinely or effectively, and many others can be developed through collaborative teams of engineers, biochemists, and materials scientists.

People will be informed about and engaged in maintaining healthy indoor environments. Occupants and facility managers of both residential and nonresidential buildings will be knowledgeable about the conditions that create problematic indoor microbial environments and how to avoid these conditions through such activities as system maintenance and cleaning. The development of personal sensors and monitors, along with guidance, education, and training, can enable occupants to understand which practices in their indoor spaces are associated with microbial proliferation and diversity, either beneficial or harmful. These efforts will be useful for identifying when a person is releasing or being exposed to undesirable microbes, such as infectious agents and allergens. Sensor data will inform intervention recommendations—for example, how occupant behavior and building operations can be altered to reduce occupant exposures. In addition, manufacturers and members of the building trades will be trained in how to construct and maintain buildings to promote and support healthy indoor environments. Best practices to reduce negative or promote positive microbial conditions will ultimately need to be embedded in building code requirements and professional guidance documents, along with the implementation and adoption of systems to support improved building maintenance.

The benefits of connections to the outdoors will be better understood and, where useful, incorporated into the design and operation of buildings. Research will improve understanding of the impact of physical and visual connections to the outdoors, as well as the variability in temperature, light, airflow, and humidity provided by a connection with the outdoor environment. Building features and environmental connections that embrace the outdoors may contribute positively or negatively to healthful indoor environments and to the optimal management of indoor microbial communities. As transportation energy shifts from combustion to electricity, for example, outdoor air quality will improve, but overlaid on such changes are the effects of climate change and urban densification; each of these changing elements may affect the overall trade-offs between the benefits and costs of outdoor air ventilation. Where beneficial, indoor–outdoor connections will be strengthened in buildings and building systems to support occupant health, energy efficiency, and resiliency. The quality of the water and air coming into buildings by design, as well as entering via unintended routes, has effects on the health of building occupants, on the building microbiome, and on building materials. Improving the quality of outdoor air and deliv-

ered water can impact the health status of building occupants and affect the indoor microbiome.¹

A RESEARCH AGENDA FOR ACHIEVING THE VISION

To realize the vision just presented, significant gaps in the knowledge needed to translate building, microbiome, and clinical research findings into practical application that have been identified in previous chapters need to be addressed. To this end, partnerships are needed across scientific disciplines, bridging U.S. and international research expertise and with communities of practice in clinical medicine and in the design, reinvention, and operation of buildings. The parameters that constitute a beneficial indoor microbiome have not yet been defined, much less the specific building designs, construction, materials, sensors, and operating approaches that will establish and sustain such a microbiome. Also necessary is to go beyond current identification and characterization of microbial taxa in indoor environmental samples to provide greater understanding of microbial functional activities and to clarify whether and how built environment microbiomes impact human health. Agreement has not yet been achieved on standardized microbial and building data to collect; on sampling and analytical protocols; and on data-sharing practices, which would facilitate cross-comparison of results. And providing solid evidence of health effects connected to indoor microbial exposures will require additional studies that contribute more quantitative and reproducible exposure and response data.

Built environment microbiomes include not only viable bacteria, viruses, and microbial eukaryotes but also dormant and dead microorganisms, microbial components, microbially produced chemicals such as volatile organic compounds (VOCs), and other metabolites. As complex as these microbiomes are, however, they are only one dimension of the still more complex exposures humans encounter indoors, which include many other types of chemicals present in buildings, as well as inorganic particulate matter, that can serve as contributing or confounding factors. Ultimately, links to human health are likely to depend on exposures to mixtures of airborne, waterborne, and surface-residing contaminants, which remain poorly characterized and understood. In addition, research will need to be conducted with occupants in diverse socioeconomic circumstances, housing conditions, and ecologic situations so potential variables can be considered and benefits that may ultimately result from the application of new knowledge can be shared.

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¹ Improvements to municipal water sources, outdoor pollution, and other such dimensions will influence built environment microbiomes; detailed discussion of these features is beyond the scope of this study.

Gaining understanding of the interacting microbial, physical, chemical, and human systems that make up the built environments in which people live and work and translating this understanding into improved building design is a long-term goal that will not be achieved immediately. Progress can be made, however, in advancing this field. The multidisciplinary research agenda presented below includes 12 research areas that are priorities for making progress in achieving 5 major objectives:

1. Characterize interrelationships among microbial communities and built environment systems of air, water, surfaces, and occupants.
2. Assess the influences of the built environment and indoor microbial exposures on the composition and function of the human microbiome, on human functional responses, and on human health outcomes.
3. Explore nonhealth impacts of interventions to manipulate microbial communities.
4. Advance the tools and research infrastructure for addressing microbiome–built environment questions.
5. Translate research into practice.

The research priorities for making progress toward each of these objectives are detailed in the following sections. Together, they constitute a research program that builds on the current state of research, identified knowledge gaps, and future directions presented in prior chapters.

Characterize Interrelationships Among Microbial Communities and Built Environment Systems of Air, Water, Surfaces, and Occupants

Buildings impact microbial colonization and transport, and further research is needed to identify the factors associated with building environments that are permissive or restrictive for bacterial, viral, and eukaryotic microbial growth and distribution. Despite examples of the known occurrence of pathogens and harmful microbes in the built environment, it is likely that most microorganisms present in a well-maintained and dry building will have no impact and that some may even have a beneficial impact on human occupants. And similarly, some microorgansims found even in damp or poorly maintained environments are likely to have no impact on human occupants. Continued work is needed to study what constitutes both harmful and healthful indoor microbiomes and to identify the aspects of building design and operation that affect microbial communities. A scientific understanding of the interrelated contributions of water, air, and surfaces to microbial distribution and transport will be critical, as will an improved understanding of the influences of the interactions and behaviors of human occupants.

Priority Research Areas

1. Improve understanding of the relationships among building site selection, design, construction, commissioning, operation, and maintenance; building occupants; and the microbial communities found in built environments. Areas for further inquiry include fuller characterization of interactions among indoor microbial communities and materials and chemicals in built environment air, water, and surfaces, along with further studies to elucidate microbial sources, reservoirs, and transport processes.
2. Incorporate the social and behavioral sciences to analyze the roles of the people who occupy and operate buildings, including their critical roles in building and system maintenance.

A better understanding of the important building attributes and a clearer identification of microbial sources associated with potential harm or benefit can drive the generation of new hypotheses and the testing of interventions aimed at control of the sources and distributions of microbial communities. Sufficient understanding of these relationships is needed as a foundation for translating knowledge into advances in building design, commissioning, and maintenance practices; corresponding professional standards and building regulations; and future investments directed at monitoring and mitigating problems or promoting benefits.

Studying human occupants and their behaviors and activities would provide further knowledge of the effects of human management of built environments. Humans will always influence the indoor environment through their presence as important sources of indoor microorganisms and through their behaviors. Occupant comfort and perception also will continue to be critical factors in building design and operation. Effective studies on built environment microbiomes likely will need to incorporate additional measures of occupant perception, behavior, and motivation. As knowledge is obtained, occupants and facilities managers will need to be educated on how their modifications of built environments affect the indoor microbiome. Risk communicators and behavioral scientists will need to be involved in the creation and implementation of this training to ensure that it is communicated effectively and does not cause misunderstanding, or even fear, among facilities managers or occupants.

Several issues can be addressed by research that meets the goals of the two priority research areas detailed above. Examples include identifying key building attributes that are critical to the survival, activity, or death of bacterial, viral, and eukaryotic microbial communities, and discovering how variations in indoor environmental conditions, such as air temperature, humidity, and the condition of water in premise plumbing and

other indoor water systems, affect these communities. The level of detail needed to capture and analyze these relationships will be substantial given the variations in these attributes in current and future built environments, compounded by occupant behaviors and facility management practices. Other research questions include understanding how ecological and evolutionary processes affect the composition, diversity, succession, stability, and activities of indoor microbiomes; understanding the modes of transport of bacterial, viral, and eukaryotic microbes in the built environment and the relevant air, water, and surface transfer mechanisms and interrelationships; and ensuring that studies include the impact of concealed spaces (e.g., inside walls and floor and ceiling cavities). For example, genomic analysis of building materials of different types and when exposed to moisture at damaging levels can further elucidate the bacterial and fungal ecology connected with these conditions and provide useful information on potential sources of indoor microbial exposures.

Assess the Influences of the Built Environment and Indoor Microbial Exposures on the Composition and Function of the Human Microbiome, on Human Functional Responses, and on Human Health Outcomes

Future research to explore the composition and behavior of microbiomes of the built environment will be critical to identifying qualities or states of built environment microbial communities that lead to healthful indoor environments for building occupants. To make substantial progress toward this goal, researchers will need to determine the nature and scale of microbial impacts on human health. Although a variety of studies in this area have been or are being conducted, much remains unknown. Important objectives include both characterizing the negative impacts of microbial communities and their constituents that have adverse effects and capturing the positive impacts of beneficial microbial communities. It will be critical to understand at least four aspects of the impacts on human health of built environment microbiomes: how individual microbes affect human health; how the community of microorganisms and mixed exposures affect human health; how changes in the community of microorganisms affect humans, and vice versa; and what the mechanisms are through which exposures result in health outcomes.

Interactions between building microbiomes and humans are inherently bidirectional. Human-associated and environmental microbiomes may affect and be affected by humans. Humans contribute to indoor microbiomes by shedding microorganisms, but the numbers and types of microorganisms they disseminate change with their health status, behavior, and other factors. Occupant density is likely to influence indoor microbial abundance and composition, while such human actions as use of chemicals and cleaning

practices will disturb and alter microbial communities. In turn, human factors such as age, genetics, and health status will likely affect human responses to microbial exposures.

Drawing on prior culture-based studies and the wealth of new data obtained through “omics” techniques, researchers have made strides in characterizing microbial taxa and their ecological dynamics in different types of built environments. But these characterizations need to be pursued further and applied to understand how built environment microbial exposures affect human health, including quantification of exposure (which microorganisms and how many) and clearer causal connections to immune and metabolic responses. Answering these and other related questions will require studies designed to provide evidence that connects environmental microbial exposures to health effects. A range of study types will be necessary to interrogate the many relationships and connections between human health and microbial exposures, including, but not limited to, controlled human exposure studies, studies using animal models, longitudinal cohort studies, intervention studies, coupled modeling and risk assessment studies, and studies designed to understand dose-response associations.

Priority Research Areas

3. Use complementary study designs—human epidemiologic observational studies (with an emphasis on collection of longitudinal data), animal model studies (for hypothesis generation and validation of human observational findings), and intervention studies—to test health-specific hypotheses.
4. Clarify how timing (stage of life), dose, and differences in human sensitivity, including genetics, affect the relationships among microbial exposures and health. These relationships may be associated with protection or risk and are likely to have different strengths of effect, parameters that are important to understand further.
5. Recognize that human exposures in built environments are complex and encompass microbial agents, chemicals, and physical materials. Develop exposure assessment approaches to address how combinations of exposures influence functional responses in different human compartments (e.g., the lungs, the brain, the peripheral nervous system, and the gut) and downstream health outcomes at different stages of life.

There are many open questions and areas of investigation that can be addressed through research to meet the goals of these research priorities. Example themes include deepening the emerging knowledge on the effects of early-life exposures to bacterial, viral, or fungal microbes in the built

environment; exploring how these exposures affect the human microbiome and human physiologic responses in ways that are beneficial to health; and elucidating the specific components required for such beneficial effects. Much less evidence currently exists for health benefits associated with later-in-life microbial exposures relative to early-life exposures, a topic that needs to be better understood. Understanding the mechanisms of action linking exposures to health effects—for example, mediated by human immune or metabolic responses—also will be critical, as will understanding the effects on health of the mixed exposures that naturally occur in the built environment, including exposures to microorganisms and microbial molecules, other built environment chemicals, and inorganic particulate matter. A number of underexplored dimensions are also associated with occupants of lower socioeconomic status, including a higher frequency of lower-quality housing and environmental conditions; a potential lack of routine building maintenance or repairs; and a lack of resources and support systems in circumstances known to affect microbial growth, such as following flooding. Research directed at understanding the effects of low socioeconomic status on the nexus of built environments, microbial communities, and occupant health will therefore be valuable.

Explore Nonhealth Impacts of Interventions to Manipulate Microbial Communities

Microorganisms and microbial communities in the built environment also have effects other than those on occupant health, such as enhanced or reduced degradation and corrosion of building materials and water systems. Although the ability to design and operate buildings that are healthful is one of the most compelling goals for research in this field, it will also be important to understand such nonhealth impacts and how they affect sustainability, costs, and other parameters important to assessing the impacts and trade-offs of building design, operation, and maintenance choices. This knowledge can inform the assessment of interventions, the development of practical guidance, and decision making.

Priority Research Area

6. Improve understanding of energy, environmental, and economic impacts of interventions that modify microbial exposures in built environments, and integrate the relevant data into existing built environment–microbial frameworks for assessing the effects of potential interventions.

Research to address this goal will need to consider diverse building types and locations, as these factors affect the materials and systems used in a building and how it is operated. Pursuing a fuller understanding of the interactions between microorganisms and building and construction materials will be useful. Smart materials or smart coatings may hold potential in this area.

The impacts and trade-offs associated with interventions in the built environment intended to affect microbial communities can have economic, energy, and sustainability dimensions beyond occupant comfort and health. Research exploring these impacts and trade-offs might consider interventions in building design and operation that include changes to building ventilation and filtration, temperature and humidity control, air and surface sterilization, and maintenance practices. Other types of interventions aimed at affecting microbial communities include the use of antimicrobial surfaces and exploration of the concept of environmental probiotics. How construction materials can be designed or tailored to address specific microbial activity is one research avenue that could be encouraged. Because the outdoor environment, including outdoor air quality and the quality of water entering a building, influence the indoor environment through building systems, studies also could usefully deepen understanding of how outdoor environmental interventions affect the assessment of indoor microbial environmental quality and occupant health. Potential interventions in this area might include, for example, landscaping to improve local biodiversity. Information gained through research addressing this priority area can also provide information about impacts on trade-offs beyond health to contribute to the development of new models, as well as evidence to support the development of future monitoring sensors and response innovations.

Advance the Tools and Research Infrastructure for Addressing Microbiome–Built Environment Questions

Identification, characterization, and quantification tools from multiple fields can be brought to bear in studying microbiome–built environment–human interactions. Advances in genomic sequencing and analysis already have improved researchers’ assessments of microbial diversity in indoor environments beyond what was previously possible. However, an important role remains for techniques that can provide complementary information on microbial functions and on relevant physical and chemical conditions within the built environment. Improvements to tools and methods will be important for analyzing the suites of bacterial, viral, fungal, and other eukaryotic microbes (such as algae and protozoa) in the built environment. Advances in modeling and in development of an agreed-upon data

commons also will provide crucial foundations for further knowledge and experimentation in the microbiomes of the built environment field.

Priority Research Areas

7. Refine molecular tools and methodologies for elucidating the identity, abundance, activity, and functions of the microbial communities present in built environments, with a focus on enabling more quantitative, sensitive, and reproducible experimental designs.

Although progress has been made in characterizing diverse communities of built environment microorganisms, a sufficiently detailed understanding of the functional activities of microbial communities and their associations with built environment and occupant factors is lacking. Understanding these associations is required to provide the basis for assessing rational interventions to promote health and sustainability. Measurement of the functional activities of microbial communities draws on information that extends beyond genomics, including information on viability, metabolism, and interactions with other microbes in the built environment community and with human physiologic systems. Molecular tool development will support improved analysis of collected samples. In addition, more studies are currently available on bacterial and fungal organisms in indoor microbiomes compared with viruses and nonfungal eukaryotes, resulting in greater knowledge of some built environment microbial populations relative to others. These gaps will need to be filled to increase the meaningful interpretation of microbial community findings.

Questions that could be addressed to help meet the goals of this research priority include further development of tools to provide improved quantitative information, such as absolute abundance data, to support modeling of community dynamics and dose-response relationships, and the development of more sensitive and reproducible tools for measuring microbial functional activities. Also useful will be the development of nondestructive measurement methods for sampling microbial characteristics in and on building materials, which will help ensure that realistic sample measurements are being taken from these materials. As noted above, collecting, measuring, and categorizing nonbacterial and nonfungal components of built environment microbiomes, such as viruses, archaea, and protists, will be valuable as well.

8. Refine building and microbiome sensing and monitoring tools, including those that enable researchers to develop building-specific hypotheses related to microbiomes and that assist in conducting intervention studies.

Both research and practical tools are needed to inform an understanding of the intersection between built environments and microbiomes. These tools can include real-time sensors and monitors in buildings to measure environmental conditions, as well as microbial properties. For example, there is a need to develop better, more rapid methods for detecting moisture levels on surfaces (water activity) and relating these levels to air humidity, material moisture content, temperatures, and dew points. Improvements in the methods used to measure indoor environmental conditions that impact the microbiome are needed as part of efforts to better characterize these interacting systems. These tools are also critical in obtaining building metadata to complement microbial data for studies aimed at understanding exposures, as well as in supporting further hypothesis generation.

Improvement in sensor technology is continually driven by technological developments in computation, materials science, engineering, and other fields. The integration of expertise from these fields with expertise from the microbiologic and clinical sciences can provide new tools to support future investigations. A variety of research can be envisioned to help meet this goal. For example, new building sensors could be developed to enhance the collection and analysis of data on a building’s physical and chemical environment, to measure human and animal occupancy, and to detect microbial growth or microbial VOCs in conjunction with the development of guidance on where to place building sensors and arrays. Sensors that can measure cumulative exposures will also be useful. The output of these sensors will support the ongoing construction and use of data-driven models.

9. Develop guidance on sampling methods and exposure assessment approaches that are suitable for testing microbiome–built environment hypotheses.
10. Develop a data commons with data description standards and provisions for data storage, sharing, and knowledge retrieval. Creating and sustaining the microbiome–built environment research infrastructure would promote transparent and reproducible research in the field, increase access to experimental data and knowledge, support the development of new analytic and modeling tools, build on current benchmarking efforts, and facilitate improved cross-study comparison.

Capturing the attributes of the built environment and its management in a consistent manner will be critical to extrapolating results from microbial research and applying them to practice and to advancing building system design and management. Defining the sampling approaches most relevant to answering particular questions will be important (e.g., when studying associations between human exposures and health outcomes).

Sample collection and handling influence the microbial results obtained from built environment studies; the establishment of common understandings and guidance to inform sampling and analysis can be valuable. In addition, standardizing the descriptions of building attributes collected in studies and using such approaches as conducting round-robin studies of standardized samples to understand laboratory-to-laboratory variability will enable comparison of results obtained by independent research groups using diverse methods.

These features would all usefully be part of a data commons for the microbiome–built environment research community. This commons will need to include an agreed-upon set of metadata to be collected in experiments, including agreed-upon criteria for recording building conditions, as well as criteria and systems, such as databases, for sharing the methods, tools, and results of microbial research. One significant challenge will be determining a balance among collecting as much detailed building, microbial, and human information as possible; experimental practicality; and cost. Efforts in these directions have already been undertaken, and potential partners for further development of a data commons may exist in multiple federal agencies and professional societies. Achieving such a data commons will require engaging researchers, microbial ecologists, building scientists, informatics experts, and others (such as health researchers) working in the field of microbiomes of the built environment to develop practices and standards that meet experimental needs and are acceptable to the community undertaking such studies. Efforts to achieve community agreement around data collection, data standards, and data sharing will need to continue, as these areas represent foundational components of future research in the field.

11. Develop new empirical, computational, and mechanistic modeling tools to improve understanding, prediction, and management of microbial dynamics and activities in built environments.

A variety of modeling tools can be implemented in studying microbiome–built environment–human interactions. These tools include models of air and water flows throughout buildings, transport pathways of air- and waterborne microorganisms, and occupant behavior. New modeling tools that improve predictions of microbial persistence, transmission, and health outcomes and incorporate data on intervention costs and tradeoffs are likely to have significant influence on the field. Mining of detailed microbiome data requires intensive computational approaches; it is not a simple task. However, it is essential to capture and account for the physical, chemical, and biologic dynamics of indoor environments so that these constraints can be statistically integrated with microbial dynamics and

microbial outcomes resulting from changes in built environment conditions can be predicted. A variety of building airflow and contaminant transport models exist, but microbial data need to be tied to these models to enable modeling of human exposures to indoor microorganisms and subsequent health impacts. Introducing microbial, indoor air quality, and health variables into the computational tools used by the building design and engineering community to monitor and predict heat, air, moisture, and contaminant transport would be one useful development. For example, incorporating experimental data into models to link building and HVAC system design with interventions aimed at promoting human and environmental health by changing microbial exposures may provide insights to support future research agendas.

Translate Research into Practice

Ongoing research efforts, along with the development of tools and methods, ultimately lead to the question of which interventions can and should be undertaken in built environments to alter buildings and their operation, built environment microbial communities, and occupant behaviors, as well as how those interventions with positive health and sustainability impacts can be promoted. Although significant fundamental research to characterize and manage microbiome–built environment interactions remains to be carried out, studies already undertaken provide a basis for further exploring these important issues. With long-term interest and investment, the field will be poised to design and test interventions in built environments that affect microbiomes in predictable ways and to develop strategies for integrating health, economic, energy, and other data to support informed decision making on which interventions to implement and at what point.

As knowledge is gained, it will be important to translate these advances into practice and to communicate and engage effectively with the diverse stakeholders that design, operate, maintain, live, and work in the built environment. These stakeholders will need guidance tailored to their goals and needs, whether it be professional practice guidelines or guidance for occupants in a range of building types. Guidance targeting occupants also will need to take account of differences in age, health status, and economic resources to inform such practices as cleaning and maintenance.

Priority Research Areas

12. Support the development of effective communication and engagement materials to convey microbiome–built environment information to diverse audiences, including guidance for professional

To continue moving toward practical application will require exploring microbiomes, built environments, and human health as an integrated system. Insights from studies in multiple areas—such as microbiology, human and built environment microbiomes, human health, indoor exposures to chemicals and particulate matter, and building system design and performance—will need to be combined. The research agenda detailed above can make progress in answering the question of what is gained by exploring built environments, as has been done in other types of ecosystems, and looking at microorganisms, buildings, and occupants in communities rather than in isolation. Answering these and other questions will require the involvement of experts from multiple fields working in concert, as well as the engagement of practitioners from the building community who are responsible for building design and operation and from the clinical community who focus on human health.

Integration across multiple disciplines to address scientific and societal challenges is a broad priority for many agencies and organizations (NAE and NASEM, 2017; NRC, 2014). Yet, achieving deep and sustained engagement that combines disciplines is difficult. A 2015 National Research Council report addresses approaches to fostering collaboration and cooperation in research teams and may contain lessons that can be applied to the built environment field (NRC, 2015). For example, the establishment of centers that bring together researchers with diverse scientific and professional backgrounds is a common approach to tackling scientific and institutional challenges associated with integrated research, and several such centers have emerged to study microbiome–built environment interactions. As with many challenging and multidisciplinary research topics, however, no single agency or organization covers the intersection of building design and operation, environmental microbiomes, and human health. Agencies or foundations interested in pursuing this research integration could consider such options as establishing collaborative funding or incorporating requirements for disciplinary integration into research solicitations. Despite these many challenges, a future informed by knowledge about indoor microbiomes holds promise for improving both human health and built environments, and it will depend on effective collaboration and on the sharing of knowledge and expertise.

REFERENCES

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