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A Word from the NAE Chair: Engineering Leadership
Editor's Note: Thoughts on the Future of the Building Microbiome
Issue Editors' Note: Microbial Challenges in the Built Environment
Engineering and Design Factors for Healthful Built Environments
Estimating Indoor Microbial Risks as Applied to Covid-19
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Microbiomes of the Built Environment
September 15, 2022 Volume 52 Issue 3
The covid-19 pandemic suddenly directed awareness to potential health impacts of the built environment of everyday living – schools, dwellings, offices, public buildings, and other spaces. This issue explores the “microbiome” of the built environment in the postpandemic reality in terms of ventilation performance, filtration, understanding and quantification of transmission risk, protection of “benign” microbes, and the important role of equity, among others.

Microenvironment-Associated Water Microbiomes and Priorities for Public Health Research

Tuesday, September 20, 2022

Author: Kerry A. Hamilton and Timothy Bartrand

Research and data are needed to improve understanding of water-related microbiomes in buildings to reduce disease outbreaks and enhance public health.

A “microenvironment” is the immediate small-scale environment of a structure or organism (or part of it), as distinct from the larger environment, and can create niches for microbial growth.1,2 Differentiating the relative risks between microenvironments in buildings is critical to ranking intervention strategies that will reduce public health risks while promoting a healthy indoor microbiome.

In this article, we highlight water microenvironments that are important from a public health perspective to (i) identify key microenvironments and microbiomes that affect public health risks, (ii) provide a qualitative assessment of the relative risk posed by water microenvironments in buildings, and (iii) identify data gaps that will inform research priorities and risk management efforts.

Water-Related Microbiomes in Buildings

As recognized in the “One Water” construct,3 water systems are a continuum connecting water sources—surface waters, groundwaters, sea-water, and brackish water (for desalination) or greywater/wastewater (for reuse)—to treatment, distribution, detention, and use in building water systems, points of use, drains, collection systems, and wastewater treatment systems. The micro-environment-associated water microbiome in buildings—plumbing systems, points of use, and features such as drains—is influenced by, but distinct from, the microbiome in other parts of the system (e.g., heating, air conditioning, ventilation).

The diversity of systems and sources points to (and data support) a wide variety of water-related microbial communities in buildings. Understanding and managing the water-related microbiome therefore require substantial data collection and synthesis.

Table 1 summarizes the water-related microbiome for key microenvironments in buildings. For 15 micro-environments it characterizes primary exposure route(s), public health significance, key microbiome characteristics and microbial community details where available, qualitative risk evaluation/priorities, data and knowledge gaps, and best management practices.

  • In terms of public health significance, disease outbreaks vary by microenvironment; they include SARS-CoV-2, norovirus, and Legionnaire’s disease, and have been associated with Clostridium difficile, Mycobacterium species, and Staphylococcus bacteria, among others.
  • Qualitative risk evaluation/priorities are designated as follows: low = unlikely to pose a nontrivial public health risk; medium = poses a nontrivial risk under some “typical” conditions or during periods of operational deficiency; high = likely to cause a nontrivial public health risk under routine operating conditions; uncertain = considerable unknown factors present challenges to designation.
  • Cited studies discuss examples of water-related microbiome characteristics and are only a sampling of the many relevant studies conducted to date.

Analysis, Key Data and Knowledge Gaps, and Research Priorities

Microenvironments are generally recognized as important because of their potential to harbor pathogens and promote their growth and because they are associated with exposures of public health consequence. We assign them a qualitative risk and priority based on their association with adverse health impacts. However, that assessment does not account for impacts on infrastructure or other non-health-related implications of the water-related microbiome. That qualification notwithstanding, the risk and priority assessments presented in table 1 can guide future data collection efforts and, equally importantly, analysis and meta-analysis of microbiome data related to priority microenvironments.

We offer the following conclusions and suggestions for measures to support progress in this important area for public health.

  • Research is needed on ways to reduce uncertainties and mitigate risks associated with understudied and/or unregulated water system microenvironments such as the unpressurized portion of showers and other shower components, bathroom drains, decorative water features, and fountains; heating, ventilation, and air conditioning systems including condensate, humidifiers, and misters; cooling towers; point-of-use devices; and certain medical devices.
  • Increased study is needed to (i) better understand the aerosol inhalation route of exposure resulting from water fixtures, systems, and/or devices; and (ii) devise more effective controls and barriers that reduce the occurrence of respiratory pathogens in building water supplies and associated accessories.
  • Improved methods for investigating microbial ecology in situ in the environment can improve understanding of disease transmission routes, prioritize microorganisms for further focus, and identify novel control strategies.
  • Use of genomic tools (e.g., whole genome sequencing) to link infections to sources can aid in identifying and prioritizing water microbiome–associated hazards.4
  • Making additional (typically non-fecal-oral) waterborne illnesses (e.g., nontuberculous mycobacteria) notifiable can increase awareness of micro-environment roles in disease.
  • To reduce public health risk in buildings, it is essential to develop, maintain, and monitor water management plans.

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* Qualitative risk evaluation/priorities: Low = unlikely to pose a nontrivial public health risk; Medium = poses a nontrivial risk under some “typical” conditions or during periods of operational deficiency; High = likely to cause a nontrivial public health risk under routine operating conditions; Uncertain = considerable unknown factors present challenges to designation.

** Self-supplied water use = water withdrawn from a ground- or surface-water source by a user rather than being obtained from a public supply.56

About the Author:Kerry Hamilton is an assistant professor, School of Sustainable Engineering and the Built Environment, and Biodesign Center for Environmental Health Engineering, Arizona State University. Timothy Bartrand is executive director, Environmental Science, Policy, and Research Institute.