Airtightness: Resistance to inward or outward air leakage through unintentional leakage in the building envelope. This air leakage is driven by differential pressures across the building envelope due to the combined effects of indoor–outdoor temperature differences, external wind, and mechanical system operation (adapted from Guyot et al., 2010).
Bacteria: Microscopic, single-celled organisms that have some biochemical and structural features different from those of animal and plant cells (IOM, 2014).
Biofilm: A thin, normally resistant, layer of microorganisms such as bacteria that forms on and coats various surfaces.1
Birth cohort study: An observational study that begins at or before birth of the subjects and continues to study the same individuals at later time points, typically on more than one occasion (Wadsworth, 2005).
Building envelope: The collective name given to the physical separators between the interior and exterior of a building, comprising such components as walls, floors, roofs, windows, skylights, and doors (adapted from Sherman, 2009).
1 See https://www.merriam-webster.com/dictionary/biofilm (accessed July 26, 2017).
Commensal organism: An organism that derives benefits from its association with humans without causing harm.
Commensalism: Two (or more) species coexist, one deriving benefit from the relationship without harm or obvious benefit to the other (IOM, 2014).
Commissioning: The process of ensuring that systems are designed, installed, functionally tested, and capable of being operated and maintained according to the owner’s operational needs (DOE, 1999, p. 9).
DNA sequencing: Determining the order of nucleotides in DNA (IOM, 2014).
Dose-response study: In the context of this report, a study that would use controlled delivery of known doses of stressors (pathogens or microbial products) to test organisms (likely animals) in order to deduce the relationship between exposed dose and the likelihood and severity of responses.
Ecology: The scientific study of the relationship between living things and their environments (IOM, 2014).
Endotoxin: A class of lipopolysaccharide-protein complexes that are an integral part of the outer membrane of Gram-negative bacteria (NRC, 2002).
Epidemiology/epidemiologic study: The study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems.2
Eukaryotic: One of the three domains of life. The two other domains, bacteria and archaea, are prokaryotes and lack several features characteristic of eukaryotes (e.g., cells containing a nucleus surrounded by a membrane and with DNA bound together by proteins [histones] into chromosomes). Animals, plants, and fungi are all eukaryotic organisms (IOM, 2014).
Fomite: A surface or other inanimate object onto which a microorganism can deposit and from which it can be transferred to a host.
Genome: The complete set of genetic information in an organism. In bacteria, this includes the chromosome(s) and plasmids (extra-chromosomal DNA molecules that can replicate autonomously within a bacterial cell) (IOM, 2014).
Genomics: The study of genes and their associated functions (IOM, 2014).
Hybrid ventilation: A ventilation approach that employs both natural and mechanical ventilation systems, potentially using different subsystems at different times of day or seasons of the year (adapted from IEA, 2006).
Infection: The invasion of the body or a part of the body by a pathogenic agent, such as a microorganism or virus. Under favorable conditions, the agent develops or multiplies, with results that may produce injurious effects (adapted from IOM, 2014).
Infiltration: The uncontrolled entry of outdoor air through unintentional openings in the building envelope, which can be driven by indoor–outdoor air pressure differences due to weather and the operation of the building (Persily, 2016).
Mechanical ventilation: The process of moving air into and within a building using ducts and powered fans or blowers, which may include means to filter, cool, heat, humidify, dehumidify, or otherwise condition the air.
Messenger RNA (mRNA): A nucleic acid molecule that is transcribed from DNA and provides instructions to the cell’s translational machinery to produce specific proteins (NASEM, 2016).
Metabolome: The census of all metabolites present in any given tissue, space, or sample (adapted from Marchesi and Ravel, 2015).
Metabolomics: Systematic global analysis of nonpeptide small molecules, such as vitamins, sugars, hormones, fatty acids, and other metabolites. It is distinct from traditional analyses that target only individual metabolites or pathways (NASEM, 2016).
Metagenome: The collection of genomes and genes from the members of a microbiota/microbial community (Marchesi and Ravel, 2015).
Metagenomics: A culture-independent method used for functional and sequence-based analysis of total environmental (community) DNA (partial from IOM, 2014).
Metaproteomics: The large-scale characterization of the entire protein complement of environmental or clinical samples at a given point in time (Marchesi and Ravel, 2015).
Metatranscriptomics: The analysis of the suite of expressed RNAs (meta-RNAs) by high-throughput sequencing of the corresponding meta-cDNAs (Marchesi and Ravel, 2015).
Microbe: A microscopic living organism, such as a bacterium, fungus, protozoan, or virus (IOM, 2014).
Microbial community/microbiota: A collection of microorganisms existing in the same place at the same time (adapted from IOM, 2014).
Microbial volatile organic compound (MVOC): A volatile organic compound produced by microorganisms.
Microbiome: Refers to the entire habitat, including the microorganisms (bacteria, archaea, lower and higher eurkaryotes, and viruses), their genomes (i.e., genes), and the surrounding environmental conditions. The microbiome is characterized by the application of one or a combination of metagenomics, metatranscriptomics, and metaproteomics together with clinical or environmental metadata (adapted from Marchesi and Ravel, 2015).
Natural ventilation: The entry of outdoor air through intentional openings in the building envelope, such as windows, doors, and vents, driven by indoor–outdoor air pressure differences due to weather and the operation of the building.
Nonpathogenic: Refers to an organism or other agent that does not cause disease (adapted from Alberts et al., 2002).
Operational taxonomic unit (OTU): The taxonomic level of sampling selected by the user to be used in a study, such as individuals, populations, species, genera, or bacterial strains (IOM, 2014).
Outdoor ventilation rate: The flow rate of outside air supplied to an indoor environment (adapted from Persily, 2016).
Outside air: Air that is brought into a building from a source outside the building.
Pathogen/pathogenic: An organism or other agent that causes disease (Alberts et al., 2002).
Penetration factor: The fraction of an outdoor, airborne contaminant that reaches the interior air volume upon passing through the building envelope.
Permissive environment: An environment having suitable conditions such that microorganisms can grow or persist.
PM2.5: Particulate matter less than 2.5 microns in diameter (NRC, 2002).
Proteomics: Analysis of the complete complements of proteins. Proteomics includes not only the identification and quantification of proteins but also the determination of their localization, modifications, interactions, and activities (NASEM, 2016).
Relative humidity: The amount of moisture in air compared with the maximal amount the air could contain at the same temperature; expressed as a percentage (NRC, 2002).
Resilience: The rate at which a community recovers to its native structure following a perturbation (IOM, 2014).
Restrictive environment: An environment that lacks suitable conditions or that contains inhibitory substances such that microbial growth does not occur and persistence is reduced.
Semivolatile organic compound (SVOC): An organic compound with a saturation vapor pressure between 10−2 and 10−8 kPa at 25°C.3 Such compounds are less volatile and tend to have a higher molecular weight than VOCs.
Shotgun sequencing: Sequencing of a genome that has been fragmented into small pieces (IOM, 2014).
Taxa: A term used to refer to all of the organisms that fall under a particular taxonomic criterion (such as kingdom, phyla, class, order, family, genera, species, or subspecies).
Taxonomic/taxonomy: The systematic classification, identification, and nomenclature of organisms (adapted from Baron, 1996).
Transcriptomics: The study of transcripts, including the number, type, and modification, many of which can impact phenotype (NASEM, 2016).
Transmissibility: The ease with which a microorganism(s) can spread from a source to a host.
3 ASTM D1356, Standard Terminology Relating to Sampling and Analysis of Atmospheres.
Transmission: The transfer of a microorganism(s) from a source to a host (adapted from Baron, 1996).
Ventilation: The process of supplying air to or removing air from a space for the purpose of controlling air contaminant levels, humidity, or temperature within the space (ASHRAE Standard 62.1).4
Virulence: A quantitative measure of pathogenicity or disease.
Virus: A small infectious agent that can replicate only inside the cells of another organism. Viruses are too small to be seen directly with a light microscope. They infect all types of organisms, from animals and plants to bacteria and archaea (IOM, 2014).
Volatile organic compound (VOC): A compound with a low molecular weight enabling its rapid evaporation into the air, where it can be inhaled. It has been defined as an organic compound with saturation vapor pressure greater than 10−2 kPa at 25°C (ASTM D1356).5
Alberts, B., A. Johnson, J. Lewis, M. Raff, K. Roberts, and P. Walter. 2002. Molecular biology of the cell, 4th ed. New York: Garland Science.
Baron, S., editor. 1996. Medical microbiology, 4th ed. Galveston, TX: University of Texas Medical Branch at Galveston.
DOE (U.S. Department of Energy). 1999. Building commissioning. The key to quality assurance. https://www.michigan.gov/documents/CIS_EO_commissioningguide_75698_7.pdf (accessed March 18, 2017).
Guyot, G., R. Carrié, and P. Schild. 2010. Stimulation of good building and ductwork airtightness through EPBD. In The final recommendations of the ASIEPI project: How to make EPB-regulations more effective? Summary report. Brussels, Belgium: European Commission. Pp. 63-82. https://ec.europa.eu/energy/intelligent/projects/sites/iee-projects/files/projects/documents/asiepi_access_the_results._en.pdf (accessed May 1, 2017).
IEA (International Energy Agency). 2006. Technical synthesis report Annex 35. Control strategies for Hybrid ventilation in new and retrofitted office and educational buildings (HYBVENT). http://www.iea-ebc.org/fileadmin/user_upload/docs/EBC_Annex_35_tsr.pdf (accessed April 18, 2017).
IOM (Institute of Medicine). 2014. Microbial ecology in states of health and disease: Workshop summary. Washington, DC: The National Academies Press.
Marchesi, J. R., and J. Ravel. 2015. The vocabulary of microbiome research: A proposal. Microbiome 3(1):31.
NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Genetically engineered crops: Experiences and prospects. Washington, DC: The National Academies Press.
4 ASHRAE 62.1-2016, Ventilation for Acceptable Indoor Air Quality.
5 ASTM D1356, Standard Terminology Relating to Sampling and Analysis of Atmospheres.
NRC (National Research Council). 2002. The airliner cabin environment and the health of passengers and crew. Washington, DC: National Academy Press.
Persily, A. K. 2016. Field measurement of ventilation rates. Indoor Air 26(1):97-111.
Sherman, M. H. 2009. Infiltration in ASHRAE’s residential ventilation standard. ASHRAE Transactions 115:887-896.
Wadsworth, M. E. J. 2005. Birth cohort studies. In Encyclopedia of biostatistics, 2nd ed., edited by P. Armitage and T. Colton. Hoboken, NJ: John Wiley & Sons, Ltd.