Architectural design influences the diversity and structure of the built environment microbiome

Buildings are complex ecosystems that house trillions of microorganisms interacting with each other, with humans and with their environment. Understanding the ecological and evolutionary processes that determine the diversity and composition of the built environment microbiome—the community of microorganisms that live indoors—is important for understanding the relationship between building design, biodiversity and human health. In this study, we used high-throughput sequencing of the bacterial 16S rRNA gene to quantify relationships between building attributes and airborne bacterial communities at a health-care facility. We quantified airborne bacterial community structure and environmental conditions in patient rooms exposed to mechanical or window ventilation and in outdoor air. The phylogenetic diversity of airborne bacterial communities was lower indoors than outdoors, and mechanically ventilated rooms contained less diverse microbial communities than did window-ventilated rooms. Bacterial communities in indoor environments contained many taxa that are absent or rare outdoors, including taxa closely related to potential human pathogens. Building attributes, specifically the source of ventilation air, airflow rates, relative humidity and temperature, were correlated with the diversity and composition of indoor bacterial communities. The relative abundance of bacteria closely related to human pathogens was higher indoors than outdoors, and higher in rooms with lower airflow rates and lower relative humidity. The observed relationship between building design and airborne bacterial diversity suggests that we can manage indoor environments, altering through building design and operation the community of microbial species that potentially colonize the human microbiome during our time indoors.     

Indoor climate and air quality

 In industrialized countries about 90% of the time is spent indoors. The ambient parameters affecting indoor thermal comfort are air temperature and humidity, air velocity, and radiant heat exchange within an enclosure. In assessing the thermal environment, one needs to consider all ambient parameters, the insulating properties of the occupants’ clothing, and the activity level of the occupants by means of heat balance models of the human body. Apart from thermal parameters, air quality (measured and perceived) is also of importance for well-being and health in indoor environments. Pollutant levels are influenced by both outdoor concentrations and by indoor emissions. Indoor levels can thus be lower (e.g. in the case of ozone and SO₂) or higher (e.g. for CO₂ and formaldehyde) than outdoor levels. Emissions from cooking play an important role, especially in developing countries. The humidity of the ambient air has a wide range of effects on the energy and water balance of the body as well as on elasticity, air quality perception, build-up of electrostatic charge and the formation or mould. However, its effect on the indoor climate is often overestimated. While air-handling systems are commonly used for achieving comfortable indoor climates, their use has also been linked to a variety of problems, some of which have received attention within the context of ”sick building syndrome”. Received: 27 October 1997 / Accepted 26 November 1997     

Microbiologic air contamination and building-associated illness

Summary Microbiologic air contamination plays, among other factors, a role in building associated illnesses i.e., hypersensitivity diseases, bacterial and fungal infections, sick building syndrome. Airborne microorganisms are separated into obligate parasites, such as the viruses and a few bacteria, that must find a suitable host within a brief period, and facultative saprophytes that are usually found in living hosts an/or in the environment (primary and opportunistic pathogens). The etiology of hypersensitivity diseases is biological allergens such as those from fungi (moulds), bacteria,Amoebae and other protozoa. Humidifiers, cold air coils and porous material belonging to mechanical ventilation system can all be reservoirs/amplifiers/disseminators for living organisms, allergens or other microbial products. Legionella is an ubiquitous bacterium in the environment. Bioaerosols from potable water and air conditioning components appear to be the source of most human infections with this organism (Legionnaire's disease and Pontiac fever).Aspergillus fumigatus has a risk of penetration indoor but affects only people with seriously impaired immunity. Responsibility of airborne moulds, bacterial endotoxins or mycotoxins in sick building syndrome complaints is unclear. Design, operation and maintenance of ventilation systems are fundamental to assure well-being to building occupants.     

Relationship between energy conservation in buildings and indoor air quality

1. 1. Problems with regard to the relationship between energy conservation and indoor air quality in buildings are discussed with a brief history of legislation and practices in Japan since the oil crisis in 1973.

2. 2. In spite of energy conservation as widely advocated the sick building syndrome has hardly been manifested in most of the office spaces in Japan owing to the Law on the Assurance of Healthy Conditions in Buildings which enforced CO₂ concentration to be kept lower than 1000 ppm.

Evaporative Cooler Use Influences Temporal Indoor Relative Humidity but Not Dust Mite Allergen Levels in Homes in a Semi-Arid Climate

Concerns about energy consumption and climate change make residential evaporative coolers a popular alternative to central air conditioning in arid and semi-arid climates. However, evaporative coolers have been shown to significantly increase indoor relative humidity and dust mite allergen levels in some studies, while showing no association in other studies. Improved measurement of temporal fluctuations in indoor relative humidity may help identify factors that promote mite growth in homes in dry climates. Dust samples and continuous indoor relative humidity measurements were collected from homes with central air conditioning and homes with evaporative coolers in Utah. Samples were collected over two seasons, winter/spring (Jan–Apr) and summer (July–Sept), 2014. Dust samples were analyzed for Der p 1 and Der f 1 using a two-site monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) analysis. Housing characteristics including age of home, occupant density, and age of mattresses, furniture, and carpeting were also measured. Positive Der p 1 or Der f 1 samples were found in 25.0% of the homes and there was no difference in mean allergen levels by type of air conditioning. Indoor relative humidity was significantly higher in homes with evaporative coolers compared to those with central air conditioning during the summer. Homes with evaporative coolers also spent significantly more time during summer above 55.0% and 65.0% relative humidity compared to central air homes, but not above 75.0%. Findings from this study suggest that increased humidity from evaporative coolers may not be sufficient to exceed the critical equilibrium humidity or maintain humidity excursions for sufficient duration in relatively larger single-family homes in semi-arid climates to support mite growth and reproduction.     

Conventional vs CO2 demand-controlled ventilation systems

1. 1. The feasibility of controlling the ventilation system using the occupant-generated carbon dioxide as an indicator of ventilation rate and indoor air quality has been investigated in an eleven storey office building.

2. 2. The study compares the indoor environment created by two different types of ventilation control systems.

3. 3. The two ventilation systems tested consisted of: a conventional system controlled by outdoor temperatures, and a demand-controlled system regulated by indoor carbon dioxide concentration.

4. 4. The results show that the CO₂-based demand-controlled ventilation system does not worsen indoor air quality and thermal comfort. It was also noticed that an energy saving of 12% was achieved using the CO₂ control system.

5. 5. The occupants perceived that their productivity is proportional to their perception of the indoor environment; indicating that higher productivity rates can be achieved by better controlling the working environment above satisfactory levels.

Airborne bacteria and fungal spores in the indoor environment. A case study in Singapore

The concentration of airborne fungal spores and bacteria as related to room temperature, humidity and occupancy levels within a library building in Singapore was determined. Measurement of indoor air quality with respect to microorganisms is of particular importance in tropical environments due to the extensive use of air‐conditioning systems and the potential implications for human health. This study has revealed a number of interesting relationships between the concentrations of fungal spores and bacteria in relation to both environmental and human factors. The levels of fungal spores measured in the indoor environment were approximately fifty times lower than those measured outside, probably because of the lowered humidity caused by air‐conditioning in the indoor environment. The variation in fungal spore concentration in the outdoor environment is likely to be due to the diurnal periodicity of spore release and the response to environmental factors such as light temperature and humidity. The indoor concentration of fungal spores in air was not clearly correlated to concentrations measured in air outside of the library building and remained relatively constant, unaffected by the difference in the numbers of occupants in the library. In contrast, the indoor concentrations of bacteria in air were approximately ten times higher than those measured outdoors, indicating a signficant internal source of bacteria. The elevated levels of indoor bacteria were primarily attributed to the number of library occupants. Increased human shedding of skin cells, ejection of microorganisms and particulates from the respiratory tract, and the transport of bacteria on suspended dust particles from floor surfaces probably accounts for the strong positive correlation between occupancy levels and the concentration of bacteria in internal air.     

Do indoor plants contribute to the aeromycota in city buildings?

Many studies have focused on the sources of fungal contamination in indoor spaces. Pathogenic fungi have been detected in the potting mix of indoor plants; however, it is unclear if plants in indoor work spaces make qualitative or quantitative contributions to the aeromycota within buildings. The current work represents a field study to determine, under realistic office conditions, whether indoor plants make a contribution to the airborne aeromycota. Fifty-five offices, within two buildings in Sydney’s central business district, were studied over two seasonal periods: autumn and spring. We found that indoor plant presence made no significant difference to either indoor mould spore counts or their species composition. No seasonal differences occurred between autumn and spring samples. Indoor spore loads were significantly lower than outdoor levels, demonstrating the efficiency of the heating, ventilation and air conditioning systems in the buildings sampled. Neither the number of plants nor the species of plant used had an influence on spore loads; however, variations of those two variables offer potential for further studies. We conclude that conservative numbers of indoor plants make no substantial contribution to building occupants exposure to fungi.     

In China, students in crowded dormitories with a low ventilation rate have more common colds: evidence for airborne transmission

Objective

To test whether the incidence of common colds among college students in China is associated with ventilation rates and crowdedness in dormitories.

Methods

In Phase I of the study, a cross-sectional study, 3712 students living in 1569 dorm rooms in 13 buildings responded to a questionnaire about incidence and duration of common colds in the previous 12 months. In Phase II, air temperature, relative humidity and CO₂ concentration were measured for 24 hours in 238 dorm rooms in 13 buildings, during both summer and winter. Out-to indoor air flow rates at night were calculated based on measured CO₂ concentrations.

Results

In Phase I, 10% of college students reported an incidence of more than 6 common colds in the previous 12 months, and 15% reported that each infection usually lasted for more than 2 weeks. Students in 6-person dorm rooms were about 2 times as likely to have an incidence of common colds ≥6 times per year and a duration ≥2 weeks, compared to students in 3-person rooms. In Phase II, 90% of the measured dorm rooms had an out-to indoor air flow rate less than the Chinese standard of 8.3 L/s per person during the heating season. There was a dose-response relationship between out-to indoor air flow rate per person in dorm rooms and the proportion of occupants with annual common cold infections ≥6 times. A mean ventilation rate of 5 L/(s•person) in dorm buildings was associated with 5% of self reported common cold ≥6 times, compared to 35% at 1 L/(s•person).

Conclusion

Crowded dormitories with low out-to indoor airflow rates are associated with more respiratory infections among college students.     

Indoor versus outdoor climate

Investigations in this field have been carried out before. Some of them will be mentioned in conjunction with this investigation. The previous investigations were about pollutants that infiltrate a building or come in with the ventilation air. This was one of the reasons that so-called natural ventilation began to be abandoned in the 1950s. Prior to that, ventilation air was taken directly from the street. In fact, the conditions that will be investigated here received attention long ago. One of the reasons that the outdoor conditions have been considered is because of the transition from older ventilation systems to current ones, where air may be taken from roof level and subjected to some treatment and cleaning. Although the subject is understood at least qualitatively, it can be interesting to look at it again. Modern calculation methods make it easier to study the problem quantitively, i.e., to calculate the indoor concentrations that can arise as a result of pollutants in the outdoor air. Such calculations can also give an idea of how long high levels of pollutants can be maintained under various circumstances.     

Dispersal in microbes: fungi in indoor air are dominated by outdoor air and show dispersal limitation at short distances

The indoor microbiome is a complex system that is thought to depend on dispersal from the outdoor biome and the occupants'' microbiome combined with selective pressures imposed by the occupants'' behaviors and the building itself. We set out to determine the pattern of fungal diversity and composition in indoor air on a local scale and to identify processes behind that pattern. We surveyed airborne fungal assemblages within 1-month time periods at two seasons, with high replication, indoors and outdoors, within and across standardized residences at a university housing facility. Fungal assemblages indoors were diverse and strongly determined by dispersal from outdoors, and no fungal taxa were found as indicators of indoor air. There was a seasonal effect on the fungi found in both indoor and outdoor air, and quantitatively more fungal biomass was detected outdoors than indoors. A strong signal of isolation by distance existed in both outdoor and indoor airborne fungal assemblages, despite the small geographic scale in which this study was undertaken (<500 m). Moreover, room and occupant behavior had no detectable effect on the fungi found in indoor air. These results show that at the local level, outdoor air fungi dominate the patterning of indoor air. More broadly, they provide additional support for the growing evidence that dispersal limitation, even on small geographic scales, is a key process in structuring the often-observed distance–decay biogeographic pattern in microbial communities.     

The Diversity and Distribution of Fungi on Residential Surfaces

The predominant hypothesis regarding the composition of microbial assemblages in indoor environments is that fungal assemblages are structured by outdoor air with a moderate contribution by surface growth, whereas indoor bacterial assemblages represent a mixture of bacteria entered from outdoor air, shed by building inhabitants, and grown on surfaces. To test the fungal aspect of this hypothesis, we sampled fungi from three surface types likely to support growth and therefore possible contributors of fungi to indoor air: drains in kitchens and bathrooms, sills beneath condensation-prone windows, and skin of human inhabitants. Sampling was done in replicated units of a university-housing complex without reported mold problems, and sequences were analyzed using both QIIME and the new UPARSE approach to OTU-binning, to the same result. Surfaces demonstrated a mycological profile similar to that of outdoor air from the same locality, and assemblages clustered by surface type. “Weedy” genera typical of indoor air, such as Cladosporium and Cryptococcus, were abundant on sills, as were a diverse set of fungi of likely outdoor origin. Drains supported more depauperate assemblages than the other surfaces and contained thermotolerant genera such as Exophiala, Candida, and Fusarium. Most surprising was the composition detected on residents’ foreheads. In addition to harboring Malassezia, a known human commensal, skin also possessed a surprising richness of non-resident fungi, including plant pathogens such as ergot (Claviceps purperea). Overall, fungal richness across indoor surfaces was high, but based on known autecologies, most of these fungi were unlikely to be growing on surfaces. We conclude that while some endogenous fungal growth on typical household surfaces does occur, particularly on drains and skin, all residential surfaces appear – to varying degrees – to be passive collectors of airborne fungi of putative outdoor origin, a view of the origins of the indoor microbiome quite different from bacteria.     

Fungal production of volatiles during growth on fiberglass.

Acoustic and thermal fiberglass insulation materials used in heating, ventilation, and air-conditioning systems were colonized with fungi in laboratory chambers. The mixed fungal population, principally Aspergillus versicolor, Acremonium obclavatum, and Cladosporium herbarum, produced odoriferous volatiles, including 2-ethyl hexanol, cyclohexane, and benzene. These volatiles may be related to poor indoor air quality and the sick building syndrome.     

Fungal colonization of fiberglass insulation in the air distribution system of a multi-story office building: VOC production and possible relationship to a sick building syndrome

Complaints characteristic of those for sick building syndrome prompted mycological investigations of a modern multi-story office building on the Gulf coast in the Southeastern United States (Houston-Galveston area). The air handling units and fiberglass duct liner of the heating, ventilating and air conditioning system of the building, without a history of catastrophic or chronic water damage, demonstrated extensive colonization withPenicillium spp andCladosporium herbarum. Although dense fungal growth was observed on surfaces within the heating-cooling system, most air samples yielded fewer than 200 CFU m^–3. Several volatile compounds found in the building air were released also from colonized fiberglass. Removal of colonized insulation from the floor receiving the majority of complaints of mouldy air and continuous operation of the units supplying this floor resulted in a reduction in the number of complaints.     

Seasonal Variation in Schools’ Indoor Air Environments and Health Symptoms among Students in an Eastern Mediterranean Climate

The indoor air quality (IAQ) in classrooms highly affects the health and productivity of students. This article aims to clarify seasonal variation in indoor environment and sick building syndromes (SBS) symptoms in an Eastern Mediterranean climate. A series of field measurements were conducted during the fall and winter seasons from October 2011 to March 2012 in 12 naturally ventilated schools located in the Gaza Strip. Data on environmental perception and health symptoms were obtained from 724 students by using a validated questionnaire. The results showed that indoor PM₁₀ and PM_2.5 concentrations were 426.3 ± 187.6 μg/m³ and 126.6 ± 94.8 μg/m³, respectively. The CO₂ concentrations and ventilation rate widely exceeded their reference values during the winter season. The prevalence rates of general symptoms were relatively high at baseline assessment in the fall season and increased significantly during follow-up in the winter season. Significant increases in disease symptoms such as mucosal irritation and pre-existing asthma symptoms among students could be related to poor indoor air quality. Five distinct groups of SBS symptoms from factor analysis of students’ related symptoms were significantly correlated with PM₁₀ and PM_2.5, CO₂, ventilation rate, and indoor temperature. As vulnerable children, this situation negatively affects their school performance and health.     

Shared Air: A Renewed Focus on Ventilation for the Prevention of Tuberculosis Transmission

Background

Despite an improvement in the overall TB cure rate from 40–74% between 1995 and 2011, TB incidence in South Africa continues to increase. The epidemic is notably disquieting in schools because the vulnerable population is compelled to be present. Older learners (age 15–19) are at particular risk given a smear-positive rate of 427 per 100,000 per year and the significant amount of time they spend indoors. High schools are therefore important locations for potential TB infection and thus prevention efforts.

Methods and Findings

Using portable carbon dioxide monitors, we measured CO₂ in classrooms under non-steady state conditions. The threshold for tuberculosis transmission was estimated using a carbon dioxide-based risk equation. We determined a critical rebreathed fraction of carbon dioxide () of 1·6%, which correlates with an indoor CO₂ concentration of 1000 ppm. These values correspond with a ventilation rate of 8·6 l/s per person or 12 air exchanges per hour (ACH) for standard classrooms of 180 m³.

Conclusions

Given the high smear positive rate of high-school adolescents in South Africa, the proposal to achieve CO₂ levels of 1000ppm through natural ventilation (in the amount 12 ACH) will not only help achieve WHO guidelines for providing children with healthy indoor environments, it will also provide a low-cost intervention for helping control the TB epidemic in areas of high prevalence.     

Effects of Classroom Ventilation Rate and Temperature on Students’ Test Scores

Using a multilevel approach, we estimated the effects of classroom ventilation rate and temperature on academic achievement. The analysis is based on measurement data from a 70 elementary school district (140 fifth grade classrooms) from Southwestern United States, and student level data (N = 3109) on socioeconomic variables and standardized test scores. There was a statistically significant association between ventilation rates and mathematics scores, and it was stronger when the six classrooms with high ventilation rates that were indicated as outliers were filtered (> 7.1 l/s per person). The association remained significant when prior year test scores were included in the model, resulting in less unexplained variability. Students’ mean mathematics scores (average 2286 points) were increased by up to eleven points (0.5%) per each liter per second per person increase in ventilation rate within the range of 0.9–7.1 l/s per person (estimated effect size 74 points). There was an additional increase of 12–13 points per each 1°C decrease in temperature within the observed range of 20–25°C (estimated effect size 67 points). Effects of similar magnitude but higher variability were observed for reading and science scores. In conclusion, maintaining adequate ventilation and thermal comfort in classrooms could significantly improve academic achievement of students.     

Impact of indoor air pollution on health,comfort and productivity of the occupants

In this special report, the possible causes of indoor air pollution and its impact on the health, comfort and productivity of the building occupant are discussed. The causes and symptoms of sick building syndrome, allergy and environmental-illnesses and building related illnesses are discussed in the context of building environments. The remediation and prevention measures examine the solution to the problems caused by indoor air pollution in buildings     

Impact of indoor air pollution on health,comfort and productivity of the occupants

In this special report, the possible causes of indoor air pollution and its impact on the health, comfort and productivity of the building occupant are discussed. The causes and symptoms of sick building syndrome, allergy and environmental illnesses and building related illnesses are discussed in the context of building environments. The remediation and prevention measures examine the solution to the problems caused by indoor air pollution in buildings.