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3 The Built Environment and Microbial Communities
Pages 91-146

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From page 91...
... Microbes enter the indoor environment pri­ marily through occupant shedding, through being carried from the outdoors through the air and water, and through microbial growth that occurs indoors. • Exposure to microbes is affected by how buildings exchange air with the environment that surrounds them.
From page 92...
... This chapter focuses on buildings and how their characteristics and occu­ ants shape the indoor microbiome. The chapter characterizes indoor p microbial sources and reservoirs associated with air, water, and building surfaces; examines how features of the building and the environment impact indoor microbial communities and occupant exposures; considers how microbial communities affect material degradation and energy use; and identifies research needs.
From page 93...
... systems; • airborne particles that have been aerosolized via HVAC operation or occupant activities, such as walking or cleaning; • outdoor air that enters through infiltration and natural or mechani cal ventilation; and • reservoirs in unfinished spaces such as crawl spaces, basements and attics, and concealed spaces (defined in Box 3-1) that are linked to occupied spaces via a range of airflow pathways.
From page 94...
... This chapter distinguishes the indoor air, water, and surface microbial reservoirs and transmission routes and details how they may lead to ­ umanh exposure and are affected by building design and operation and by occupant actions. Where appropriate, it notes the distinctive features of building systems and management that lead to unique issues for residential buildings and for small and large commercial buildings.
From page 95...
... High-rise, multifamily residential buildings are more likely to incorporate some amount of mechanical outdoor air intake, often supplied to hallways, but the HVAC and outdoor air systems in such buildings vary greatly. While the microbial environments of commercial buildings -- including offices, schools, and other nonindustrial workplaces -- share some similarities with residences, there are a number of important differences.
From page 96...
... , and mechanical exhausts, all of which may increase the entry of outdoor air and microbes, as well as air and microbial migration between interior spaces. Both residential and commercial buildings are characterized by widespread use of carpeting and textiles -- known reservoirs of microbes -- as well as maintenance and cleaning practices that may limit or promote the accumulation of microbial material and microbial growth, depending on frequency and the methods and materials used.
From page 97...
... A growing body of evidence suggests that teacher productivity and student learning may also be affected by indoor air quality. • Well-designed, -constructed, and -maintained building envelopes are critical to the control and reduction of excess moisture and mold growth.
From page 98...
... In some cases, buildings fail to deliver acceptable indoor environmental quality even at the time of their initial occupation. This issue has led, especially in the case of larger-scale commercial and other buildings, to a growing commitment to "building commissioning"4 -- a process intended to ensure that "systems are designed, installed, functionally tested, and capable of being operated and maintained according to the owner's operational needs" (DOE, 1999, p.
From page 99...
... . These chambers, as well as the ISS, can serve as specialized test chambers to examine potential built environment interventions and their effect on the indoor microbiome.
From page 100...
... INDOOR AIR SOURCES AND RESERVOIRS OF MICROBES Air is a critical transport vehicle of microbes and their metabolites in the built environment because it connects surfaces, water, and dust to what occupants inhale, inadvertently ingest, or absorb through their skin. The sources of the microbial communities that make up the microbiome of the built environment include indoor and outdoor sources of bacteria, fungi, and viruses, and the movement of air is a significant factor in their distribution.
From page 101...
... . Increased attention has been paid to indoor air chemistry in recent years, revealing many important mechanisms affecting the fate and transport of airborne chemical contaminants within buildings (Morrison, 2015; Nazaroff and Goldstein, 2015; Weschler, 2011, 2016)
From page 102...
... . Infiltration is driven by differences between indoor and outdoor air pressures, which vary with outdoor weather conditions, including wind velocity and direction relative to building exterior surfaces and their exposure to the wind, as well as differences between outdoor and indoor air temperatures.
From page 103...
... . The design and placement of outdoor air intakes for mechanical ventilation systems can also influence the indoor microbial environment.
From page 104...
... . S Existing Ventilation Standards and Measured Performance Existing standards and building regulations include requirements for outdoor air ventilation rates and exhaust airflow rates for different building types and space uses intended to provide standards for model code requirements (ASHRAE, 2016a,b)
From page 105...
... Considering only minimum outdoor air intake operation and accounting for the lower occupancy levels, the mean ventilation rate was about 11 L/s per person at default occupancy values in ASHRAE Standard 62.1, which is based on achieving <20 percent dissatisfaction with perceived indoor air quality (ASHRAE, 2016a)
From page 106...
... . Where heating demand dominates design considerations, indoor air will be less humid than ­ colder outdoor air because of the reduced relative humidity from warming of the air.11 Where air conditioning is dominant, indoor air will be cooler than the air outdoors, and management of the air conditioning system will determine the moisture content of the indoor air and its potential effect on airborne microbes.
From page 107...
... . Indoor Air Sources and Reservoirs of Microbes: Summary of Findings Air leakage through unintentional openings in the building envelope, internal migration of air between zones, the distribution of air by mechanical conditioning and ventilation systems, and natural ventilation affect the association between air and the indoor microbiome.
From page 108...
... . The implications of the shift to sealed buildings for indoor air quality, occu­ pant satisfaction and performance, and indoor microbiomes have yet to be thoroughly researched.
From page 109...
... . The following sections address six examples of water-related sources of potentially problematic microbes: • premise plumbing •  water heaters hot • cooling towers, cooling coils, and drain pans • leakage, flooding, and wet building materials • indoor water sources and airborne moisture generators • indoor humidity Premise Plumbing Water piped into buildings can come from municipal water treatment plants, wells, groundwater, or surface water sources.
From page 110...
... of water in the premise plumbing system. Building features and human behaviors that increase the likelihood of stagnant water are important to consider because stagnant water supports microbial growth.
From page 111...
... 617–618) note that "Acanthamoeba, ­ ycobacterium avium M complex, and Pseudomonas aeruginosa can also grow within water heating systems and cause thousands of cases of infections annually." Investigators have studied microbial communities in domestic hot water heated to different temperatures in systems with varying levels of use (Ji et al., 2017; Rhoads, 2017; Rhoads et al., 2015)
From page 112...
... Because of their rooftop location, which may be near or upwind of outdoor air intakes, cooling towers can release L pneumophila into the airstream taken in by the ventilation systems, leading to illness in the buildings where they are located.
From page 113...
... The building codes are intended to govern design and issuance of building permits, but not operating conditions in occupied buildings. Leakage, Flooding, and Wet Building Materials Water can also enter a building from a host of unintentional sources, including enclosure leakage and flooding, plumbing leakage, rising damp, condensation, and human activities.
From page 114...
... . Indoor Water Sources and Airborne Moisture Generators In addition to rain penetration with the possibility of both direct wetting of materials and standing water, microbial growth can be supported 14  Gypsum board is "the generic name for a family of panel products that consist of a noncombustible core, composed primarily of gypsum, and a paper surfacing on the face, back and long edges" (https://www.gypsum.org/technical/using-gypsum-board-for-walls-andceilings/using-gypsum-board-for-walls-and-ceilings-section-i [accessed July 17, 2017]
From page 115...
... , and they produce aerosolized bacteria in the surface water close to the head of the human o ­ ccupant/user of the spa. In addition, increased humidity levels indoors can lead to higher water vapor on interior surfaces and within building materials.
From page 116...
... Inside walls, attics, and roofing assemblies, the moisture content of materials is affected by seasonal surface temperatures, with cooler internal surfaces collecting and retaining more moisture than warm surfaces. Air-conditioned interiors have increased moisture absorption and therefore higher surface water activity and more potential to support microbial growth.
From page 117...
... and Climate Change, the Indoor Environment, and Health (IOM, 2011) , the committee identified the need for more research on water quality supplied and delivered by premise plumbing; microbial management in building hot water heaters, cooling towers, cooling coils, and drain pans; leakage and flooding that results in moisture damage, especially in houses; indoor water fixtures, features, and airborne moisture generators; and the detection of mold and moisture inside building assemblies, especially walls and roof assemblies.
From page 118...
... Indoor surfaces that can support microbial growth -- including floor, wall, and ceiling materials, as well as plumbing and HVAC components -- ­ are important in designing and maintaining buildings to manage microbial communities to human advantage. This section focuses on the relationship of building surfaces to ­ icrobes m that impact human health.
From page 119...
... Rotavirus Day care centers, pediatric ward (8) Toys, phones, toilet handles, sinks, water fountains, door handles, play areas, refrigerator handles, water play tables, thermometers, play mats (8, 15, 38, 70)
From page 120...
... Tables 3-2 and 3-3 illustrate the commonalities and differences among fomites of concern in residential buildings versus commercial buildings and hospitals. These tables also list surfaces of concern on which occupants sit and lie, from chairs to couches and bedding, where hand-to-mouth and mouth-to-mouth transfer is also possible.
From page 121...
... TABLE 3-3  Hospital High-Touch Surfaces and Bacterial Reservoirs Patient area Bed rails, tray table, call boxes, telephone, bedside tables, patient chair, intravenous (IV) pole, floor, light switches, glove box, air, air exhaust filter Patient Sink, faucet handles, inside faucet head, hot tap water, cold tap water, light restroom switches, door knob, handrails, toilet seats, flush lever, bed pan cleaning equipment, floor, air, air exhaust filter Additional IV pump control panel, monitor control panel, monitor touch screen, monitor equipment cables, ventilator control panel, blood pressure cuff, janitorial equipment Water Cold tap water, hot tap water, water used to clean floors Patient Stool sample, nasal swab, hand Staff Nasal swab, bottom of shoe, dominant hand, cell phone, pager, iPad, computer mouse, work phone, shirt cuff, stethoscope Travel areas Corridor floor, corridor wall, steps, stairwell door knobs, stairwell door kick plates, elevator buttons, elevator floor, handrails, air Lobby Front desk surface, chairs, coffee tables, floor, air Public Floor, door handles, sink controls, sink bowl, soap dispenser, towel dispenser, restroom toilet seats, toilet lever, stall door lock, stall door handle, urinal flush lever, air, air exhaust filter SOURCE: Smith et al., 2013, Table A5-2.
From page 122...
... • Occupant proximity and • Plants or water features interaction • Number of occupants • Connections to other rooms • Air temperature • Relative humidity • Percentage recirculated air •  change rate Air SOURCE: Smith et al., 2013, Table A5-3. surface sterilization with antimicrobial agents, such as bleach, etha •  nol, and peroxide; hands-free lights, doors, and elevators; •  protective covers, easy-to-disinfect surfaces, and built-in periodic •  cleaning reminders for keyboards and computer mouses in medical environments; ultraviolet (UV)
From page 123...
... In a chamber bioaerosol study, Adams and colleagues (2015) compared the relative abundance of bacterial and fungal taxa in indoor air, outdoor air, and dust.
From page 124...
... 5104) indicate that research on this topic highlights "the importance of reducing indoor emissions associated with occupancy, potentially through more regular and effective floor cleaning and through the choice of flooring materials that limit particle resuspension." There is strong evidence that human occupancy increases fungal and bacterial concentrations in indoor air through resuspension.
From page 125...
... . Microbial community analyses conducted in schools demonstrate that resuspended floor dust is enriched in bacteria and fungi associated with human skin and that surface-based resuspension may be a major source of airborne fungal allergens, rather than infiltration of these microbes into buildings from outdoor air (Hospodsky et al., 2015; Yamamoto et al., 2015)
From page 126...
... The primary risk factors for the dampness that supports microbial growth differ across climates, geographic areas, and building types. This dampness can also damage building materials and furnishings, causing or exacerbating their release of chemicals and nonbiologic particles.
From page 127...
... review of the literature on indoor microbial growth across building materials and sampling and analysis methods finds that the bioreceptivity of materials is determined most strongly by their water activity, chemical composition (in particular, nutrient sources) , pH, and surface physical properties (porosity, surface roughness, and the like)
From page 128...
... Building Surfaces and Reservoirs of Microbes: Summary of Findings Surfaces constitute a critical reservoir for microbial growth and transfer in the built environment. The specification, design, and maintenance of building surfaces need to be critically evaluated to reduce microbial sources and transfers that occur by (1)
From page 129...
... BUILDING CODES AND STANDARDS THAT MAY AFFECT THE MICROBIOME Regulations and Guidance The regulatory environment for indoor environmental conditions in the United States is defined by several different federal agencies, as well as by state and local authorities. The Occupational Safety and Health Administration has purview over worker health and safety in all workplaces, but it has no specific requirements related to indoor air quality in nonindustrial workplaces such as offices and schools.
From page 130...
... Table 3-5 lists some of the green design standards, guidelines, and certifications used in the United States that are aimed at improving site, energy, water, materials, and indoor environmental quality and address microbial communities. These standards and guidelines promote building features that reduce adverse exposures to microbes, including increased ventilation rates with better filtration of outside air to remove particulate matter, commissioning and continuous commissioning of building mechanical systems, design for cleanability and quality cleaning practices, walk-off mats for reducing particulate matter and pest intrusion, cooling coil and cooling tower management, and increased access to the outdoors for occupants.
From page 131...
... THE INFLUENCE OF CLIMATE AND CLIMATE CHANGE ON THE BUILT ENVIRONMENT AND MICROBIAL COMMUNITIES The indoor microbiome depends strongly on climate, and a better understanding of how buildings are designed and used in different climates is essential for improving understanding of the relevant issues. Different 22  "Grey water" and "black water" are both forms of wastewater generated from human activities.
From page 132...
... In cold winter climates, for example, the cold outdoor air contains relatively little water vapor. When this air infiltrates a heated building, the relative humidity declines, and the indoor air is perceived to be very dry.
From page 133...
... . Changes in outdoor air temperature and humidity over time impact the ability of the system to maintain desirable indoor air temperatures and to control indoor humidity, and if these changes are large enough, the system may not be able to provide the desired indoor conditions.
From page 134...
... SUMMARY OBSERVATIONS AND KNOWLEDGE GAPS Summary Observations The composition and viability of indoor microbial communities are dependent on the physical attributes and environmental conditions of the buildings in which they are located. Understanding the conditions in which microbial communities form and are maintained requires consideration of
From page 135...
... To take one simple example, limiting outdoor air sources by tightening the building envelope without otherwise providing adequate ventilation could increase indoor moisture and airborne microbial levels, resulting in enhanced microbial growth on damp interior surfaces. Little is known about what constitutes a "good" indoor microbiome and even less about which building characteristics might foster one.
From page 136...
... Improve understanding of how building attributes are associated with microbial communities, and establish a common set of build ing and environmental data for collection in future research efforts. The building attributes that are associated with various microbial communities need to be gathered for the full range of building types in different climates to foster a better understanding of the differences between how buildings are designed and how they actu ally function -- an important element of determining how to achieve healthy indoor microbiomes.
From page 137...
... The committee's literature review identified a number of knowledge gaps associated with indoor microbial sources and reservoirs. For air sources, the implications of the shift to more completely sealed buildings for indoor air quality, occupant satisfaction and performance, and in door microbiomes have yet to be thoroughly researched.
From page 138...
... 2015. Chamber bioaerosol study: Outdoor air and human occupants as sources of indoor airborne microbes.
From page 139...
... 2016b. ANSI/ASHRAE Standard 62.2: Ventilation and acceptable indoor air qual ity in low-rise residential buildings.
From page 140...
... 2017a. Commercial Buildings Energy Consumption Survey (CBES)
From page 141...
... 2017b. Location of outdoor air intakes and exhaust.
From page 142...
... 2012. Human occupancy as a source of indoor airborne bacteria.
From page 143...
... 2014a. Indoor airborne bacterial communities are influenced by ventilation, occupancy, and outdoor air source.
From page 144...
... Indoor Air 22(4)
From page 145...
... Indoor Air 14(S7)
From page 146...
... 2014. A review of indoor microbial growth across building materials and sampling and analysis methods.


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