Author: Meier Jan
The field of microbiology of the built environment includes the study of microbial diversity, interactions, and microbial ecology in indoor spaces such as workspaces, homes, hospitals, and other indoor spaces. In fact, microorganisms exist in the air, on surfaces and building materials. They are usually dispersed by humans, animals, and outdoor sources. Human health and well-being can be hugely impacted by the built environment as we spent most of our time indoors. [1] Present microorganisms, for instance molds and bacteria, can lead to allergic reactions, respiratory problems, and other health issues. On the other hand, exposure to some microorganisms can boost the immune system and promote overall health. Some of the key areas of research include the impact of building design and construction on microbial diversity, the role of ventilation systems in microbial ecology, and the potential for microbial communities to influence the spread of infectious diseases. [2] This article first highlights some sources and impacts of microorganisms in the built environment on human health. Then several beneficial effects of microbes are presented. Finally, some interventions are proposed to reduce exposure to hazardous microbes.
The indoor environment can harbor potentially infectious microorganisms such as viruses, bacteria, fungi, protozoa, and algae. Those organisms can vary in their mode of transmissibility, virulence, and mode of spread, which directly affects the mode and effectiveness of infection control. Inhalation of microorganisms carried or resuspended in indoor air, as well as via fomites, are important routes of transmission. Multiple modes of transmission often occur for a particular organism and are contingent on the state of the building and the behavior of occupants. Understanding transmissibility and virulence patterns can help in infection control interventions. [2]
Air is a critical transport vehicle of microbes and their metabolites in the built environment. The communities can therefore be sourced both from outdoors as well as indoors. The crucial role of the air consists in distributing these microbes by connecting surfaces, water, and dust to what humans inhale or ingest. Four main factors in the air transport of indoor and outdoor microbes are met.
- Air leakage through unintentional openings
- Internal migration of air
- Mechanical ventilation
- Natural ventilation
Buildings are typically ventilated using a combination of envelope infiltration, mechanical, and natural ventilation. Hybrid ventilation systems become increasingly popular for achieving energy savings while maintaining a comfortable indoor environment. [2]
Microbes rely on water for their growth and survival. The presence of water can sustain their life and promote reproduction and growth. Water from public or private supply sources can contain pathogens like Legionella pneumophila and Mycobacterium avium, which pose health risks to occupants. It is intentionally brought into the building through premise plumbing. Although buildings are designed to remain dry, water is present in mainly two forms, such as liquid and vapor depending on air and surface temperatures, physical properties of materials, and water concentration. The unwanted liquid water can result from plumbing leaks, leaks in the exterior building walls, roofs, floor slabs, crawl spaces, or basement, as well as capillary action that draws groundwater through building materials. Water vapor mainly mitigates into a building due to air pressure differences or activities such as showering, cooking, and washing clothes. [2]
Moisture within a building can create an environment that is conductive to the growth of mold, bacteria, and other microorganisms. Additionally, dampness can also harbor living organisms such as dust mites, which can contribute to respiratory problems. The pollutants do not only come from biological sources but can also arise from deterioration of building materials, which can be accelerated by dampness. The list below summarizes sufficient evident and clinical evident outcomes of damp buildings on health. They were established by the three review publications IOM (Institute of Medicine) 2004, Mendell et al. 2011 [3], and WHO (World Health Organization) 2009.
- Upper respiratory (nasal and throat) tract symptoms
- Wheeze
- Cough
- Exacerbation of existing asthma
- Hypersensitivity pneumonitis
However, some health outcomes still lack sufficient evidence, such as altered lung function, airflow obstruction, skin symptoms, gastrointestinal problems, cancer, rheumatologic and immune diseases and more. Building-related water damage, indoor point sources of dampness and water, as well as poor maintenance of buildings lead to indoor moisture problems. Under these circumstances, proliferation of microbial communities is increased. Noninfectious adverse allergic and nonallergic respiratory responses are caused, particularly in susceptible populations such as children and people with preexisting asthma.
Nevertheless, beneficial effects of microbes exist. The interest in the potential protective effects of indoor environmental microbes has largely increased in the last two decades. Studies conducted in farm communities have shown that lower risk of allergic asthma is correlated with certain microbial exposures at home during early life. [10]
Another study demonstrated that dog-associated dust and its associated bacterial communities may reduce atopy symptoms in mice, indicating that young children living in homes with dogs may be less likely to develop asthma. [5] Furthermore, the microbes living on animals may shape immune responses on skin, airway mucosal surfaces, and in the gut. Alternatively, green building design could potentially impact occupant health by improving air quality. There are also attempts to link green building design to neurocognitive outcomes showing fewer self-reported lost schooldays or workdays, less disturbed sleep, sadness, nervousness, and restlessness. [2]
Microbiology of the built environment is a very complex discipline that has numerous interactions with building materials, chemistry, ventilation systems and further subjects. We must be aware that the human body is on constant touch with microorganisms. To limit microbiome-related issues, WELL Building Standard listed the following checklist that should be taken into account. [6]
Air:
- Microbe and mold control
- Healthy entrance
- Cleaning protocol
- Moisture management
- Humidity control
- Antimicrobial surfaces
- Cleanable environment
- Cleaning Equipment
Water:
- Fundamental water quality
- Public water additives
- Periodic water quality testing
- Water treatment
Nourishment:
- Hand washing
- Food contamination
Furthermore, the first and best option to fight pollutants is limiting the source. However, reducing exposure is also key to limit contact and potential infection. The main challenges are to better measure exposure to microbes as well as performing better epidemiological studies. [1]
References
[1] EPFL, CIVIL-460 Indoor Air Quality and Ventilation, Spring Semester 2023
[2] National Academic Press (US), Microbiomes of the Built Environment, 2017 August 16
[3] Mendell et al. 2011, Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence, National Library of Medicine 119 (6) 748–756
[4] Ege et al. 2011, Exposure to Environmental Microorganisms and Childhood Asthma, New England Journal of Medicine 364:701-709
[5] Fall et al. 2015, Early Exposure to Dogs and Farm Animals and the Risk of Childhood Asthma, National Library of Medicine 169 (11)
[6] Delos Living LLC, The WELL Building Standard, May 2016
Jan Meier, CIVIL-460 Indoor Air Quality and Ventilation Spring Semester 2023