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[[File:Airborne Precautions poster.pdf|alt=A red poster with illustrations and the text: "AIRBORNE PRECAUTIONS. EVERYONE MUST: Clean their hands, including before entering and when leaving the room. Put on a fit-tested N-95 or higher level respirator before room entry. Remove respirator after exiting the room and closing the door. Door to room must remain closed."|thumb|upright=1.3|A poster outlining precautions for airborne transmission in healthcare settings. It is intended to be posted outside rooms of patients with an infection that can spread through airborne transmission.<ref name=":5">{{Cite web|url=https://www.cdc.gov/infectioncontrol/basics/transmission-based-precautions.html|title=Transmission-Based Precautions|date=2016-01-07|website=U.S. [[Centers for Disease Control and Prevention]]|language=en-us|access-date=2020-03-31}}</ref>]]
[[File:Airborne Precautions poster.pdf|alt=A red poster with illustrations and the text: "AIRBORNE PRECAUTIONS. EVERYONE MUST: Clean their hands, including before entering and when leaving the room. Put on a fit-tested N-95 or higher level respirator before room entry. Remove respirator after exiting the room and closing the door. Door to room must remain closed."|thumb|upright=1.3|A poster outlining precautions for airborne transmission in healthcare settings. It is intended to be posted outside rooms of patients with an infection that can spread through airborne transmission.<ref name=":5">{{Cite web|url=https://www.cdc.gov/infectioncontrol/basics/transmission-based-precautions.html|title=Transmission-Based Precautions|date=2016-01-07|website=U.S. [[Centers for Disease Control and Prevention]]|language=en-us|access-date=2020-03-31}}</ref>]]
[[File:Safe Spaces - how to reduce virus transmission indoors - 9hP41EaypD4.webm|thumb|thumbtime=0:41|290px|Video explainer on reducing airborne pathogen transmission indoors]]
[[File:Safe Spaces - how to reduce virus transmission indoors - 9hP41EaypD4.webm|thumb|thumbtime=0:41|290px|Video explainer on reducing airborne [[pathogen]] transmission indoors]]
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'''Airborne or aerosol transmission''' is [[Transmission (medicine)|transmission of an infectious disease]] through small [[particulates|particles]] suspended in the air.<ref>{{Cite web|url=https://www.cdc.gov/infectioncontrol/pdf/guidelines/isolation-guidelines-H.pdf|title=2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings|website=CDC|access-date=2019-02-07|page=19|vauthors=Siegel JD, Rhinehart E, Jackson M, Chiarello L, ((Healthcare Infection Control Practices Advisory Committee))|quote=Airborne transmission occurs by dissemination of either airborne droplet nuclei or small particles in the respirable size range containing infectious agents that remain infective over time and distance}}</ref> Infectious diseases capable of airborne transmission include many of considerable importance both in [[Human medicine|human]] and [[veterinary medicine]]. The relevant [[pathogen|infectious agent]] may be [[virus]]es, [[bacteria]], or [[Fungus|fungi]], and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, [[Toilet plume|flushing toilets]], or any activities which generate [[aerosol]] particles or [[Drop (liquid)|droplets]].


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'''Airborne transmission''' or '''aerosol transmission''' is [[Transmission (medicine)|transmission of an infectious disease]] through small [[particulates|particles]] suspended in the air.<ref>{{Cite web|url=https://www.cdc.gov/infectioncontrol/pdf/guidelines/isolation-guidelines-H.pdf|title=2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings|website=CDC|access-date=2019-02-07|page=19|vauthors=Siegel JD, Rhinehart E, Jackson M, Chiarello L, ((Healthcare Infection Control Practices Advisory Committee))|quote=Airborne transmission occurs by dissemination of either airborne droplet nuclei or small particles in the respirable size range containing infectious agents that remain infective over time and distance}}</ref> Infectious diseases capable of airborne transmission include many of considerable importance both in [[Human medicine|human]] and [[veterinary medicine]]. The relevant [[pathogen|infectious agent]] may be [[virus]]es, [[bacteria]], or [[Fungus|fungi]], and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, [[Toilet plume|flushing toilets]], or any activities which generate [[aerosol]] particles or [[Drop (liquid)|droplets]].
This is the transmission of diseases via transmission of an infectious agent, and does not include diseases caused by [[air pollution]].


==Infectious aerosols: physical terminology==
Aerosol transmission has traditionally been considered distinct from transmission by [[respiratory droplet|droplet]]s, but this distinction is no longer used.<ref name=":1">{{Cite journal|last1=Tang|first1=Julian W.|last2=Marr|first2=Linsey C.|last3=Li|first3=Yuguo|last4=Dancer|first4=Stephanie J.|date=2021-04-14|title=Covid-19 has redefined airborne transmission|url=https://www.bmj.com/content/373/bmj.n913|journal=BMJ|language=en|volume=373|pages=n913|doi=10.1136/bmj.n913|issn=1756-1833|pmid=33853842|s2cid=233235666}}</ref><ref name="McNeill">{{cite journal |last1=McNeill |first1=VF |title=Airborne Transmission of SARS-CoV-2: Evidence and Implications for Engineering Controls |journal=Annual Review of Chemical and Biomolecular Engineering |date=10 June 2022 |volume=13 |issue=1 |pages=123–140 |doi=10.1146/annurev-chembioeng-092220-111631 |pmid=35300517 |s2cid=247520571 |url=https://doi.org/10.1146/annurev-chembioeng-092220-111631 |access-date=13 June 2022 |issn=1947-5438}}</ref> Respiratory droplets were thought to rapidly fall to the ground after emission:<ref name="ZhangChen20202">{{cite journal | vauthors = Zhang N, Chen W, Chan PT, Yen HL, Tang JW, Li Y | title = Close contact behavior in indoor environment and transmission of respiratory infection | journal = Indoor Air | volume = 30 | issue = 4 | pages = 645–661 | date = July 2020 | pmid = 32259319 | doi = 10.1111/ina.12673 | s2cid = 215408351 }}</ref> but smaller droplets and aerosols also contain live infectious agents, and can remain in the air longer and travel farther.<ref name="McNeill"/>
Individuals generate aerosols and droplets across a wide range of sizes and concentrations, and the amount produced varies widely by person and activity.<ref name=":0">{{cite book | veditors = Shelton-Davenport M, Pavlin J, Saunders J, Staudt A | collaboration = Environmental Health Matters Initiative, National Academies of Sciences, Engineering, and Medicine |url=https://www.nap.edu/catalog/25958|title=Airborne Transmission of SARS-CoV-2: Proceedings of a Workshop in Brief|date=2020-10-22|publisher=National Academies Press|isbn=978-0-309-68408-8 |location=Washington, D.C.|doi=10.17226/25958 | pmid = 33119244 | vauthors = Staudt A, Saunders J, Pavlin J, Shelton-Davenport M | s2cid = 236828761 }}</ref> Larger droplets greater than 100 [[Micrometre|μm]] usually settle within 2 m.<ref name=":0" /><ref name="ZhangChen20202"/> Smaller particles can carry airborne pathogens for extended periods of time. While the concentration of airborne pathogens is greater within 2m, they can travel farther and concentrate in a room.<ref name="McNeill"/>
Aerosol transmission has traditionally been considered distinct from transmission by [[respiratory droplet|droplet]]s, but this distinction is no longer used.<ref name=":1">{{cite journal | vauthors = Tang JW, Marr LC, Li Y, Dancer SJ | title = Covid-19 has redefined airborne transmission | journal = BMJ | volume = 373 | pages = n913 | date = April 2021 | pmid = 33853842 | doi = 10.1136/bmj.n913 | s2cid = 233235666 | doi-access = free }}</ref><ref name="McNeill">{{cite journal | vauthors = McNeill VF | title = Airborne Transmission of SARS-CoV-2: Evidence and Implications for Engineering Controls | journal = Annual Review of Chemical and Biomolecular Engineering | volume = 13 | issue = 1 | pages = 123–140 | date = June 2022 | pmid = 35300517 | doi = 10.1146/annurev-chembioeng-092220-111631 | s2cid = 247520571 }}</ref> Respiratory droplets were thought to rapidly fall to the ground after emission:<ref name="ZhangChen20202">{{cite journal | vauthors = Zhang N, Chen W, Chan PT, Yen HL, Tang JW, Li Y | title = Close contact behavior in indoor environment and transmission of respiratory infection | journal = Indoor Air | volume = 30 | issue = 4 | pages = 645–661 | date = July 2020 | pmid = 32259319 | doi = 10.1111/ina.12673 | bibcode = 2020InAir..30..645Z | s2cid = 215408351 | doi-access = free }}</ref> but smaller droplets and aerosols also contain live infectious agents, and can remain in the air longer and travel farther.<ref name="McNeill"/><ref>{{Cite journal | vauthors = Pal A, Biswas R, Pal R, Sarkar S, Mukhopadhyay A |date=2023-01-01 |title=A novel approach to preventing SARS-CoV-2 transmission in classrooms: A numerical study |url=https://aip.scitation.org/doi/10.1063/5.0131672 |journal=Physics of Fluids |volume=35 |issue=1 |pages=013308 |doi=10.1063/5.0131672 |s2cid=254779734 |issn=1070-6631}}</ref><ref>{{cite journal | vauthors = Biswas R, Pal A, Pal R, Sarkar S, Mukhopadhyay A | title = Risk assessment of COVID infection by respiratory droplets from cough for various ventilation scenarios inside an elevator: An OpenFOAM-based computational fluid dynamics analysis | journal = Physics of Fluids | volume = 34 | issue = 1 | pages = 013318 | date = January 2022 | pmid = 35340680 | pmc = 8939552 | doi = 10.1063/5.0073694 | arxiv = 2109.12841 | bibcode = 2022PhFl...34a3318B }}</ref> Individuals generate aerosols and droplets across a wide range of sizes and concentrations, and the amount produced varies widely by person and activity.<ref name=":0">{{cite book | veditors = Shelton-Davenport M, Pavlin J, Saunders J, Staudt A | collaboration = Environmental Health Matters Initiative, National Academies of Sciences, Engineering, and Medicine |url=https://www.nap.edu/catalog/25958|title=Airborne Transmission of SARS-CoV-2: Proceedings of a Workshop in Brief|date=2020-10-22|publisher=National Academies Press|isbn=978-0-309-68408-8 |location=Washington, D.C.|doi=10.17226/25958 | pmid = 33119244 | vauthors = Staudt A, Saunders J, Pavlin J, Shelton-Davenport M | s2cid = 236828761 }}</ref> Larger droplets greater than 100 [[Micrometre|μm]] usually settle within 2 m.<ref name=":0" /><ref name="ZhangChen20202"/> Smaller particles can carry airborne pathogens for extended periods of time. While the concentration of airborne pathogens is greater within 2m, they can travel farther and concentrate in a room.<ref name="McNeill"/>


The traditional size cutoff of 5 [[Micrometre|μm]] between airborne and respiratory droplets has been discarded, as exhaled particles form a continuum of sizes whose fates depend on environmental conditions in addition to their initial sizes. This error has informed hospital based transmission based precautions for decades.<ref name=":0"/> Indoor respiratory secretion transfer data suggest that droplets/aerosols in the 20 [[Micrometre|μm]] size range initially travel with the air flow from cough jets and air conditioning like aerosols,<ref name=":2">{{Cite journal|last=Hunziker|first=Patrick|date=2021-10-01|title=Minimising exposure to respiratory droplets, 'jet riders' and aerosols in air-conditioned hospital rooms by a 'Shield-and-Sink' strategy|url=https://bmjopen.bmj.com/content/11/10/e047772|journal=BMJ Open|language=en|volume=11|issue=10|pages=e047772|pmid=34642190| doi=10.1136/bmjopen-2020-047772|s2cid=229291099 |issn=2044-6055}}</ref> but fall out gravitationally at a greater distance as "jet riders".<ref>{{Cite journal| vauthors = Hunziker P |date=2020-12-16|title=Minimizing exposure to respiratory droplets, 'jet riders' and aerosols in air-conditioned hospital rooms by a 'Shield-and-Sink' strategy |doi=10.1101/2020.12.08.20233056|s2cid=229291099}}</ref> As this size range is most efficiently filtered out in the [[nasal mucosa]],<ref>{{Cite journal| vauthors = Kesavanathan J, Swift DL |date=January 1998|title=Human Nasal Passage Particle Deposition: The Effect of Particle Size, Flow Rate, and Anatomical Factors |journal=Aerosol Science and Technology|volume=28|issue=5|pages=457–463|doi=10.1080/02786829808965537|bibcode=1998AerST..28..457K|issn=0278-6826}}</ref> the primordial infection site in [[COVID-19]], aerosols/droplets<ref>{{Cite journal|last1=Adlish|first1=John I.|last2=Neuhold|first2=Piero|last3=Surrente|first3=Riccardo|last4=Tagliapietra|first4=Luca J.|date=18 June 2021|title=RNA Identification and Detection of Nucleic Acids as Aerosols in Air Samples by Means of Photon and Electron Interactions|journal=Instruments|language=en|volume=5|issue=2|pages=23|doi=10.3390/instruments5020023|arxiv=2105.00340|doi-access=free}}</ref> in this size range may contribute to driving the [[COVID-19 pandemic]].
The traditional size cutoff of 5 [[Micrometre|μm]] between airborne and respiratory droplets has been discarded, as exhaled particles form a continuum of sizes whose fates depend on environmental conditions in addition to their initial sizes. This error has informed hospital based transmission based precautions for decades.<ref name=":0"/> Indoor respiratory secretion transfer data suggest that droplets/aerosols in the 20 [[Micrometre|μm]] size range initially travel with the air flow from cough jets and air conditioning like aerosols,<ref name=":2">{{cite journal | vauthors = Hunziker P | title = Minimising exposure to respiratory droplets, 'jet riders' and aerosols in air-conditioned hospital rooms by a 'Shield-and-Sink' strategy | journal = BMJ Open | volume = 11 | issue = 10 | pages = e047772 | date = October 2021 | pmid = 34642190 | pmc = 8520596 | doi = 10.1136/bmjopen-2020-047772 |medrxiv=10.1101/2020.12.08.20233056| s2cid = 229291099 }}</ref> but fall out gravitationally at a greater distance as "jet riders".<ref name=":2" /> As this size range is most efficiently filtered out in the [[nasal mucosa]],<ref>{{Cite journal| vauthors = Kesavanathan J, Swift DL |date=January 1998|title=Human Nasal Passage Particle Deposition: The Effect of Particle Size, Flow Rate, and Anatomical Factors |journal=Aerosol Science and Technology|volume=28|issue=5|pages=457–463|doi=10.1080/02786829808965537|bibcode=1998AerST..28..457K|issn=0278-6826}}</ref> the primordial infection site in [[COVID-19]], aerosols/droplets<ref>{{Cite journal| vauthors = Adlish JI, Neuhold P, Surrente R, Tagliapietra LJ |date=18 June 2021|title=RNA Identification and Detection of Nucleic Acids as Aerosols in Air Samples by Means of Photon and Electron Interactions|journal=Instruments|language=en|volume=5|issue=2|pages=23|doi=10.3390/instruments5020023|arxiv=2105.00340|doi-access=free}}</ref> in this size range may contribute to driving the [[COVID-19 pandemic]].


==Overview==
==Overview==
Airborne diseases can be transmitted from one individual to another through the air. The pathogens transmitted may be any kind of [[Microorganism|microbe]], and they may be spread in aerosols, dust or droplets. The aerosols might be generated from sources of [[infection]] such as the bodily secretions of an infected individual, or biological wastes. Infectious aerosols may stay suspended in air currents long enough to travel for considerable distances; [[sneeze]]s, for example, can easily project infectious droplets for dozens of feet (ten or more meters).<ref>{{Cite web|url=https://www.chicagotribune.com/opinion/ct-xpm-2014-04-19-ct-sneeze-germs-edit-20140419-story.html|title = Ack! Sneeze germs carry farther than you think| website=[[Chicago Tribune]] }}</ref>
Airborne diseases can be transmitted from one individual to another through the air. The pathogens transmitted may be any kind of [[Microorganism|microbe]], and they may be spread in aerosols, dust or droplets. The aerosols might be generated from sources of [[infection]] such as the bodily secretions of an infected individual, or biological wastes. Infectious aerosols may stay suspended in air currents long enough to travel for considerable distances; [[sneeze]]s, for example, can easily project infectious droplets for dozens of feet (ten or more meters).<ref>{{Cite web|url=https://www.chicagotribune.com/opinion/ct-xpm-2014-04-19-ct-sneeze-germs-edit-20140419-story.html|title = Ack! Sneeze germs carry farther than you think| website=[[Chicago Tribune]] | date=19 April 2014 }}</ref>


Airborne pathogens or [[allergens]] typically enter the body via the [[nose]], [[throat]], [[Paranasal sinuses|sinuses]] and [[lung]]s. Inhalation of these pathogens affects the respiratory system and can then spread to the rest of the body. Sinus congestion, coughing and sore throats are examples of inflammation of the upper respiratory airway. Air pollution plays a significant role in airborne diseases. [[Pollutants]] can influence lung function by increasing air way inflammation.<ref>{{cite web|url=http://www.nutramed.com/Air/airborne_diseases.htm |title=Airborne diseases |url-status=dead |access-date=21 May 2013 |archive-url=https://web.archive.org/web/20120628073116/http://www.nutramed.com/Air/airborne_diseases.htm |archive-date=28 June 2012 }}</ref>
Airborne pathogens or [[allergens]] typically enter the body via the [[nose]], [[throat]], [[Paranasal sinuses|sinuses]] and [[lung]]s. Inhalation of these pathogens affects the respiratory system and can then spread to the rest of the body. Sinus congestion, coughing and sore throats are examples of inflammation of the upper respiratory airway. Air pollution plays a significant role in airborne diseases. [[Pollutants]] can influence lung function by increasing air way inflammation.<ref>{{cite web|url=http://www.nutramed.com/Air/airborne_diseases.htm |title=Airborne diseases |url-status=dead |access-date=21 May 2013 |archive-url=https://web.archive.org/web/20120628073116/http://www.nutramed.com/Air/airborne_diseases.htm |archive-date=28 June 2012 }}</ref>


Common infections that spread by airborne transmission include COVID-19;<ref>{{Cite web|title=COVID-19: epidemiology, virology and clinical features|url=https://www.gov.uk/government/publications/wuhan-novel-coronavirus-background-information/wuhan-novel-coronavirus-epidemiology-virology-and-clinical-features|access-date=2020-10-24|website=GOV.UK|language=en}}</ref> [[measles morbillivirus]],<ref>{{cite journal | vauthors = Riley EC, Murphy G, Riley RL | title = Airborne spread of measles in a suburban elementary school | journal = American Journal of Epidemiology | volume = 107 | issue = 5 | pages = 421–32 | date = May 1978 | pmid = 665658 | doi = 10.1093/oxfordjournals.aje.a112560 }}</ref> [[chickenpox virus]];<ref name=":4">{{Cite web|url=https://eportal.mountsinai.ca/Microbiology/faq/transmission.shtml|title=FAQ: Methods of Disease Transmission|website=[[Mount Sinai Hospital (Toronto)]]|access-date=2020-03-31}}</ref> ''[[Mycobacterium tuberculosis]]'', [[influenza virus]], [[enterovirus]], [[norovirus]] and less commonly [[coronavirus]], [[Adenoviridae|adenovirus]], and possibly [[respiratory syncytial virus]].<ref name=":3">{{cite journal | vauthors = La Rosa G, Fratini M, Della Libera S, Iaconelli M, Muscillo M | title = Viral infections acquired indoors through airborne, droplet or contact transmission | journal = Annali dell'Istituto Superiore di Sanità | volume = 49 | issue = 2 | pages = 124–32 | date = 2013-06-01 | pmid = 23771256 | doi = 10.4415/ANN_13_02_03 }}</ref>
Common infections that spread by airborne transmission include [[SARS-CoV-2]];<ref>{{Cite web|title=COVID-19: epidemiology, virology and clinical features|url=https://www.gov.uk/government/publications/wuhan-novel-coronavirus-background-information/wuhan-novel-coronavirus-epidemiology-virology-and-clinical-features|access-date=2020-10-24|website=GOV.UK|language=en}}</ref> [[measles morbillivirus]],<ref>{{cite journal | vauthors = Riley EC, Murphy G, Riley RL | title = Airborne spread of measles in a suburban elementary school | journal = American Journal of Epidemiology | volume = 107 | issue = 5 | pages = 421–432 | date = May 1978 | pmid = 665658 | doi = 10.1093/oxfordjournals.aje.a112560 }}</ref> [[chickenpox virus]];<ref name=":4">{{Cite web|url=https://eportal.mountsinai.ca/Microbiology/faq/transmission.shtml|title=FAQ: Methods of Disease Transmission|website=[[Mount Sinai Hospital (Toronto)]]|access-date=2020-03-31}}</ref> ''[[Mycobacterium tuberculosis]]'', [[influenza virus]], [[enterovirus]], [[norovirus]] and less commonly other species of [[coronavirus]], [[Adenoviridae|adenovirus]], and possibly [[respiratory syncytial virus]].<ref name=":3">{{cite journal | vauthors = La Rosa G, Fratini M, Della Libera S, Iaconelli M, Muscillo M | title = Viral infections acquired indoors through airborne, droplet or contact transmission | journal = Annali dell'Istituto Superiore di Sanità | volume = 49 | issue = 2 | pages = 124–132 | date = 2013-06-01 | pmid = 23771256 | doi = 10.4415/ANN_13_02_03 }}</ref> Some pathogens which have more than one mode of transmission are also [[Anisotropy|anisotropic]], meaning that their different modes of transmission can cause different kinds of diseases, with different levels of severity. Two examples are the bacterias [[Yersinia pestis]] (which causes [[Plague (disease)|plague]]) and [[Francisella tularensis]] (which causes [[Tularemia|tularaemia]]), which both can cause severe pneumonia, if transmitted via the airborne route through inhalation.<ref>{{cite journal | vauthors = Tellier R, Li Y, Cowling BJ, Tang JW | title = Recognition of aerosol transmission of infectious agents: a commentary | journal = BMC Infectious Diseases | volume = 19 | issue = 1 | pages = 101 | date = January 2019 | pmid = 30704406 | pmc = 6357359 | doi = 10.1186/s12879-019-3707-y | doi-access = free }}</ref>


Poor ventilation enhances transmission by allowing aerosols to spread undisturbed in an indoor space.<ref>{{cite journal | vauthors = Noakes CJ, Beggs CB, Sleigh PA, Kerr KG | title = Modelling the transmission of airborne infections in enclosed spaces | journal = Epidemiology and Infection | volume = 134 | issue = 5 | pages = 1082–91 | date = October 2006 | pmid = 16476170 | pmc = 2870476 | doi = 10.1017/S0950268806005875 }}</ref> Crowded rooms are more likely to contain an infected person. The longer a susceptible person stays in such a space, the greater chance of transmission. Airborne transmission is complex, and hard to demonstrate unequivocally<ref>{{cite journal | vauthors = Tang JW, Bahnfleth WP, Bluyssen PM, Buonanno G, Jimenez JL, Kurnitski J, Li Y, Miller S, Sekhar C, Morawska L, Marr LC, Melikov AK, Nazaroff WW, Nielsen PV, Tellier R, Wargocki P, Dancer SJ | display-authors = 6 | title = Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) | journal = The Journal of Hospital Infection | volume = 110 | pages = 89–96 | date = April 2021 | pmid = 33453351 | pmc = 7805396 | doi = 10.1016/j.jhin.2020.12.022 }}</ref> but the [[Wells-Riley model]] can be used to make simple estimates of infection probability.<ref>{{cite journal | vauthors = Sze To GN, Chao CY | title = Review and comparison between the Wells-Riley and dose-response approaches to risk assessment of infectious respiratory diseases | journal = Indoor Air | volume = 20 | issue = 1 | pages = 2–16 | date = February 2010 | pmid = 19874402 | pmc = 7202094 | doi = 10.1111/j.1600-0668.2009.00621.x }}</ref>
Poor ventilation enhances transmission by allowing aerosols to spread undisturbed in an indoor space.<ref>{{cite journal | vauthors = Noakes CJ, Beggs CB, Sleigh PA, Kerr KG | title = Modelling the transmission of airborne infections in enclosed spaces | journal = Epidemiology and Infection | volume = 134 | issue = 5 | pages = 1082–1091 | date = October 2006 | pmid = 16476170 | pmc = 2870476 | doi = 10.1017/S0950268806005875 }}</ref> Crowded rooms are more likely to contain an infected person. The longer a susceptible person stays in such a space, the greater chance of transmission. Airborne transmission is complex, and hard to demonstrate unequivocally<ref>{{cite journal | vauthors = Tang JW, Bahnfleth WP, Bluyssen PM, Buonanno G, Jimenez JL, Kurnitski J, Li Y, Miller S, Sekhar C, Morawska L, Marr LC, Melikov AK, Nazaroff WW, Nielsen PV, Tellier R, Wargocki P, Dancer SJ | display-authors = 6 | title = Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) | journal = The Journal of Hospital Infection | volume = 110 | pages = 89–96 | date = April 2021 | pmid = 33453351 | pmc = 7805396 | doi = 10.1016/j.jhin.2020.12.022 }}</ref> but the [[Wells-Riley model]] can be used to make simple estimates of infection probability.<ref>{{cite journal | vauthors = Sze To GN, Chao CY | title = Review and comparison between the Wells-Riley and dose-response approaches to risk assessment of infectious respiratory diseases | journal = Indoor Air | volume = 20 | issue = 1 | pages = 2–16 | date = February 2010 | pmid = 19874402 | pmc = 7202094 | doi = 10.1111/j.1600-0668.2009.00621.x }}</ref>


Some airborne diseases can affect non-humans. For example, [[Newcastle disease]] is an avian disease that affects many types of domestic poultry worldwide that is airborne.<ref>{{cite journal | vauthors = Mitchell BW, King DJ | title = Effect of negative air ionization on airborne transmission of Newcastle disease virus | journal = Avian Diseases | volume = 38 | issue = 4 | pages = 725–32 | date = October–December 1994 | pmid = 7702504 | doi = 10.2307/1592107 | jstor = 1592107 }}</ref>
Some airborne diseases can affect non-humans. For example, [[Newcastle disease]] is an avian disease that affects many types of domestic poultry worldwide that is airborne. [[Bird|Poultry animals]] are often also airborne.<ref>{{cite journal | vauthors = Mitchell BW, King DJ | title = Effect of negative air ionization on airborne transmission of Newcastle disease virus | journal = Avian Diseases | volume = 38 | issue = 4 | pages = 725–732 | date = October–December 1994 | pmid = 7702504 | doi = 10.2307/1592107 | jstor = 1592107 }}</ref>


Airborne transmission can be classified as obligate, preferential, or opportunistic. Obligate airborne infections spread only through aerosols; the most common example of this category is tuberculosis. Preferential airborne infections, such as chicken pox, can be obtained through different routes, but mainly by aerosols. Opportunistic airborne infections such as influenza typically transmit through other routes; however, under favourable conditions, aerosol transmission can occur.<ref>{{cite journal | vauthors = Seto WH | title = Airborne transmission and precautions: facts and myths | language = English | journal = The Journal of Hospital Infection | volume = 89 | issue = 4 | pages = 225–8 | date = April 2015 | pmid = 25578684 | doi = 10.1016/j.jhin.2014.11.005 | pmc = 7132528 }}</ref> Because the drying process can damage the pathogens, the number of airborne diseases is limited.<ref name=":4" />
It has been suggested that airborne transmission should be classified as being either obligate, preferential, or opportunistic, although there is limited research that show the importance of each of these categories.<ref>{{cite journal | vauthors = Kutter JS, Spronken MI, Fraaij PL, Fouchier RA, Herfst S | title = Transmission routes of respiratory viruses among humans | journal = Current Opinion in Virology | volume = 28 | pages = 142–151 | date = February 2018 | pmid = 29452994 | pmc = 7102683 | doi = 10.1016/j.coviro.2018.01.001 }}</ref> Obligate airborne infections spread only through aerosols; the most common example of this category is tuberculosis. Preferential airborne infections, such as chicken pox, can be obtained through different routes, but mainly by aerosols. Opportunistic airborne infections such as influenza typically transmit through other routes; however, under favourable conditions, aerosol transmission can occur.<ref>{{cite journal | vauthors = Seto WH | title = Airborne transmission and precautions: facts and myths | language = English | journal = The Journal of Hospital Infection | volume = 89 | issue = 4 | pages = 225–228 | date = April 2015 | pmid = 25578684 | pmc = 7132528 | doi = 10.1016/j.jhin.2014.11.005 }}</ref>


==Transmission==
==Transmission efficiency==
Environmental factors influence the efficacy of airborne disease transmission; the most evident environmental conditions are [[temperature]] and [[relative humidity]].<ref name="Ma">{{cite journal |last1=Ma |first1=Y |last2=Pei |first2=S |last3=Shaman |first3=J |last4=Dubrow |first4=R |last5=Chen |first5=K |title=Role of meteorological factors in the transmission of SARS-CoV-2 in the United States |journal=Nature Communications |date=14 June 2021 |volume=12 |issue=1 |pages=3602 |doi=10.1038/s41467-021-23866-7 |pmid=34127665 |pmc=8203661 |language=en |issn=2041-1723}}</ref><ref name="Božič">{{cite journal |last1=Božič |first1=A |last2=Kanduč |first2=M |title=Relative humidity in droplet and airborne transmission of disease |journal=Journal of Biological Physics |date=1 March 2021 |volume=47 |issue=1 |pages=1–29 |doi=10.1007/s10867-020-09562-5 |pmid=33564965 |pmc=7872882 |language=en |issn=1573-0689}}</ref>
Environmental factors influence the efficacy of airborne disease transmission; the most evident environmental conditions are [[temperature]] and [[relative humidity]].<ref name="Ma">{{cite journal | vauthors = Ma Y, Pei S, Shaman J, Dubrow R, Chen K | title = Role of meteorological factors in the transmission of SARS-CoV-2 in the United States | journal = Nature Communications | volume = 12 | issue = 1 | pages = 3602 | date = June 2021 | pmid = 34127665 | pmc = 8203661 | doi = 10.1038/s41467-021-23866-7 | bibcode = 2021NatCo..12.3602M }}</ref><ref name="Božič">{{cite journal | vauthors = Božič A, Kanduč M | title = Relative humidity in droplet and airborne transmission of disease | journal = Journal of Biological Physics | volume = 47 | issue = 1 | pages = 1–29 | date = March 2021 | pmid = 33564965 | pmc = 7872882 | doi = 10.1007/s10867-020-09562-5 }}</ref>
The transmission of airborne diseases is affected by all the factors that influence temperature and humidity, in both meteorological (outdoor) and human (indoor) environments. Circumstances influencing the spread of droplets containing infectious particles can include pH, salinity, wind, air pollution, and solar radiation as well as human behavior.<ref name="Sooryanarain"/>
The transmission of airborne diseases is affected by all the factors that influence temperature and humidity, in both meteorological (outdoor) and human (indoor) environments. Circumstances influencing the spread of droplets containing infectious particles can include pH, salinity, wind, air pollution, and solar radiation as well as human behavior.<ref name="Sooryanarain"/>


Airborne infections usually land in the respiratory system, with the agent present in aerosols (infectious particles < 5&nbsp;µm in diameter).<ref>{{Cite web|title=Prevention of hospital-acquired infections|url=https://www.who.int/csr/resources/publications/whocdscsreph200212.pdf|website=World Health Organization (WHO)}}</ref> This includes dry particles, often the remnant of an evaporated wet particle called nuclei, and wet particles.
Airborne infections usually land in the respiratory system, with the agent present in aerosols (infectious particles < 5&nbsp;μm in diameter).<ref>{{Cite web|title=Prevention of hospital-acquired infections|url=https://www.who.int/csr/resources/publications/whocdscsreph200212.pdf|website=World Health Organization (WHO)}}</ref> This includes dry particles, often the remnant of an evaporated wet particle called nuclei, and wet particles.
* Relative humidity (RH) plays an important role in the evaporation of droplets and the distance they travel. 30 μm droplets evaporate in seconds.<ref name="pmid32301491">{{cite journal|vauthors=Bahl P, Doolan C, de Silva C, Chughtai AA, Bourouiba L, MacIntyre CR|date=April 2020|title=Airborne or droplet precautions for health workers treating COVID-19?|journal=The Journal of Infectious Diseases|doi=10.1093/infdis/jiaa189|pmc=7184471|pmid=32301491}}</ref> The CDC recommends a minimum of 40% RH indoors<ref name="pmid23460865">{{cite journal|vauthors=Noti JD, Blachere FM, McMillen CM, Lindsley WG, Kashon ML, Slaughter DR, Beezhold DH|date=2013|title=High humidity leads to loss of infectious influenza virus from simulated coughs|journal=PLOS ONE|volume=8|issue=2|pages=e57485|bibcode=2013PLoSO...857485N|doi=10.1371/journal.pone.0057485|pmc=3583861|pmid=23460865|doi-access=free}}</ref> to significantly reduce the infectivity of aerosolized virus. An ideal humidity for preventing aerosol respiratory viral transmission at room temperature appears to be between 40% and 60% RH. If the relative humidity goes below 35% RH, infectious virus stays longer in the air.
* Relative humidity (RH) plays an important role in the evaporation of droplets and the distance they travel. 30 μm droplets evaporate in seconds.<ref name="pmid32301491">{{cite journal | vauthors = Bahl P, Doolan C, de Silva C, Chughtai AA, Bourouiba L, MacIntyre CR | title = Airborne or Droplet Precautions for Health Workers Treating Coronavirus Disease 2019? | journal = The Journal of Infectious Diseases | volume = 225 | issue = 9 | pages = 1561–1568 | date = May 2022 | pmid = 32301491 | pmc = 7184471 | doi = 10.1093/infdis/jiaa189 }}</ref> The CDC recommends a minimum of 40% RH indoors<ref name="pmid23460865">{{cite journal | vauthors = Noti JD, Blachere FM, McMillen CM, Lindsley WG, Kashon ML, Slaughter DR, Beezhold DH | title = High humidity leads to loss of infectious influenza virus from simulated coughs | journal = PLOS ONE | volume = 8 | issue = 2 | pages = e57485 | date = 2013 | pmid = 23460865 | pmc = 3583861 | doi = 10.1371/journal.pone.0057485 | doi-access = free | bibcode = 2013PLoSO...857485N }}</ref> to significantly reduce the infectivity of aerosolized virus. An ideal humidity for preventing aerosol respiratory viral transmission at room temperature appears to be between 40% and 60% RH. If the relative humidity goes below 35% RH, infectious virus stays longer in the air.
* The number of rainy days<ref name="ncbi.nlm.nih.gov">{{cite journal | vauthors = Pica N, Bouvier NM | title = Environmental factors affecting the transmission of respiratory viruses | journal = Current Opinion in Virology | volume = 2 | issue = 1 | pages = 90–5 | date = February 2012 | pmid = 22440971 | pmc = 3311988 | doi = 10.1016/j.coviro.2011.12.003 }}</ref> (more important than total precipitation);<ref name="ReferenceA">{{cite journal | vauthors = Rodríguez-Rajo FJ, Iglesias I, Jato V | title = Variation assessment of airborne Alternaria and Cladosporium spores at different bioclimatical conditions | journal = Mycological Research | volume = 109 | issue = Pt 4 | pages = 497–507 | date = April 2005 | pmid = 15912938 | doi = 10.1017/s0953756204001777 | citeseerx = 10.1.1.487.177 }}</ref><ref>{{cite journal | vauthors = Peternel R, Culig J, Hrga I | title = Atmospheric concentrations of Cladosporium spp. and Alternaria spp. spores in Zagreb (Croatia) and effects of some meteorological factors | journal = Annals of Agricultural and Environmental Medicine | volume = 11 | issue = 2 | pages = 303–7 | year = 2004 | pmid = 15627341 }}</ref> mean daily sunshine hours;<ref name="pmid10879421">{{cite journal | vauthors = Sabariego S, Díaz de la Guardia C, Alba F | title = The effect of meteorological factors on the daily variation of airborne fungal spores in Granada (southern Spain) | journal = International Journal of Biometeorology | volume = 44 | issue = 1 | pages = 1–5 | date = May 2000 | pmid = 10879421 | doi = 10.1007/s004840050131 | s2cid = 17834418 | bibcode = 2000IJBm...44....1S }}</ref> latitude and altitude<ref name="ReferenceA" /> are relevant when assessing the possibility of spread of airborne disease. Some infrequent or exceptional events influence the dissemination of airborne diseases, including tropical storms, [[Tropical cyclone|hurricanes]], [[typhoon]]s, or [[monsoon]]s.<ref name="ReferenceB">{{cite journal | vauthors = Hedlund C, Blomstedt Y, Schumann B | title = Association of climatic factors with infectious diseases in the Arctic and subarctic region--a systematic review | journal = Global Health Action | volume = 7 | pages = 24161 | year = 2014 | pmid = 24990685 | pmc = 4079933 | doi = 10.3402/gha.v7.24161 }}</ref>
* The number of rainy days<ref name="ncbi.nlm.nih.gov">{{cite journal | vauthors = Pica N, Bouvier NM | title = Environmental factors affecting the transmission of respiratory viruses | journal = Current Opinion in Virology | volume = 2 | issue = 1 | pages = 90–95 | date = February 2012 | pmid = 22440971 | pmc = 3311988 | doi = 10.1016/j.coviro.2011.12.003 }}</ref> (more important than total precipitation);<ref name="ReferenceA">{{cite journal | vauthors = Rodríguez-Rajo FJ, Iglesias I, Jato V | title = Variation assessment of airborne Alternaria and Cladosporium spores at different bioclimatical conditions | journal = Mycological Research | volume = 109 | issue = Pt 4 | pages = 497–507 | date = April 2005 | pmid = 15912938 | doi = 10.1017/s0953756204001777 | citeseerx = 10.1.1.487.177 }}</ref><ref>{{cite journal | vauthors = Peternel R, Culig J, Hrga I | title = Atmospheric concentrations of Cladosporium spp. and Alternaria spp. spores in Zagreb (Croatia) and effects of some meteorological factors | journal = Annals of Agricultural and Environmental Medicine | volume = 11 | issue = 2 | pages = 303–307 | year = 2004 | pmid = 15627341 }}</ref> mean daily sunshine hours;<ref name="pmid10879421">{{cite journal | vauthors = Sabariego S, Díaz de la Guardia C, Alba F | title = The effect of meteorological factors on the daily variation of airborne fungal spores in Granada (southern Spain) | journal = International Journal of Biometeorology | volume = 44 | issue = 1 | pages = 1–5 | date = May 2000 | pmid = 10879421 | doi = 10.1007/s004840050131 | s2cid = 17834418 | bibcode = 2000IJBm...44....1S }}</ref> latitude and altitude<ref name="ReferenceA" /> are relevant when assessing the possibility of spread of airborne disease. Some infrequent or exceptional events influence the dissemination of airborne diseases, including tropical storms, [[Tropical cyclone|hurricanes]], [[typhoon]]s, or [[monsoon]]s.<ref name="ReferenceB">{{cite journal | vauthors = Hedlund C, Blomstedt Y, Schumann B | title = Association of climatic factors with infectious diseases in the Arctic and subarctic region--a systematic review | journal = Global Health Action | volume = 7 | pages = 24161 | year = 2014 | pmid = 24990685 | pmc = 4079933 | doi = 10.3402/gha.v7.24161 }}</ref>
* Climate affects temperature, winds and relative humidity, the main factors affecting the spread, duration and infectiousness of droplets containing infectious particles.<ref name="Ma"/> The influenza virus spreads easily in the [[Northern hemisphere|Northern Hemisphere]] winter due to climate conditions that favour the infectiousness of the virus.<ref name="Sooryanarain">{{cite journal |last1=Sooryanarain |first1=H |last2=Elankumaran |first2=S |title=Environmental Role in Influenza Virus Outbreaks |journal=Annual Review of Animal Biosciences |date=16 February 2015 |volume=3 |issue=1 |pages=347–373 |doi=10.1146/annurev-animal-022114-111017 |pmid=25422855 |url=https://doi.org/10.1146/annurev-animal-022114-111017 |access-date=13 June 2022 |issn=2165-8102}}</ref>
* Climate affects temperature, winds and relative humidity, the main factors affecting the spread, duration and infectiousness of droplets containing infectious particles.<ref name="Ma"/> The influenza virus spreads easily in the [[Northern hemisphere|Northern Hemisphere]] winter due to climate conditions that favour the infectiousness of the virus.<ref name="Sooryanarain">{{cite journal | vauthors = Sooryanarain H, Elankumaran S | title = Environmental role in influenza virus outbreaks | journal = Annual Review of Animal Biosciences | volume = 3 | issue = 1 | pages = 347–373 | date = 16 February 2015 | pmid = 25422855 | doi = 10.1146/annurev-animal-022114-111017 | doi-access = free }}</ref>
* Isolated weather events decrease the concentration of airborne [[Spore|fungal spores]]; a few days later, number of spores increases exponentially.<ref>{{cite journal | vauthors = Khan NN, Wilson BL | title = An environmental assessment of mold concentrations and potential mycotoxin exposures in the greater Southeast Texas area | journal = Journal of Environmental Science and Health. Part A, Toxic/Hazardous Substances & Environmental Engineering | volume = 38 | issue = 12 | pages = 2759–72 | year = 2003 | pmid = 14672314 | doi = 10.1081/ESE-120025829 | s2cid = 6906183 }}</ref>
* Isolated weather events decrease the concentration of airborne [[Spore|fungal spores]]; a few days later, number of spores increases exponentially.<ref>{{cite journal | vauthors = Khan NN, Wilson BL | title = An environmental assessment of mold concentrations and potential mycotoxin exposures in the greater Southeast Texas area | journal = Journal of Environmental Science and Health. Part A, Toxic/Hazardous Substances & Environmental Engineering | volume = 38 | issue = 12 | pages = 2759–2772 | year = 2003 | pmid = 14672314 | doi = 10.1081/ESE-120025829 | bibcode = 2003JESHA..38.2759K | s2cid = 6906183 }}</ref>
* Socioeconomics has a minor role in airborne disease transmission. In cities, airborne disease spreads more rapidly than in rural areas and urban outskirts. Rural areas generally favor higher airborne fungal dissemination.<ref>{{cite journal | vauthors = Tang JW | title = The effect of environmental parameters on the survival of airborne infectious agents | journal = Journal of the Royal Society, Interface | volume = 6 Suppl 6 | pages = S737-46 | date = December 2009 | pmid = 19773291 | pmc = 2843949 | doi = 10.1098/rsif.2009.0227.focus }}</ref>
* Socioeconomics has a minor role in airborne disease transmission. In cities, airborne disease spreads more rapidly than in rural areas and urban outskirts. Rural areas generally favor higher airborne fungal dissemination.<ref>{{cite journal | vauthors = Tang JW | title = The effect of environmental parameters on the survival of airborne infectious agents | journal = Journal of the Royal Society, Interface | volume = 6 | issue = Suppl 6 | pages = S737–S746 | date = December 2009 | pmid = 19773291 | pmc = 2843949 | doi = 10.1098/rsif.2009.0227.focus }}</ref>
* Proximity to large bodies of water such as rivers and lakes can enhance airborne disease.<ref name="ReferenceB" />
* Proximity to large bodies of water such as rivers and lakes can enhance airborne disease.<ref name="ReferenceB" />
* A direct association between insufficient ventilation rates and increased COVID-19 transmission has been observed. Prior to COVID-19, standards for ventilation systems focused more on supplying sufficient oxygen to a room, rather than disease-related aspects of air quality.<ref name="McNeill" />
* A direct association between insufficient ventilation rates and increased COVID-19 transmission has been observed. Prior to COVID-19, standards for ventilation systems focused more on supplying sufficient oxygen to a room, rather than disease-related aspects of air quality.<ref name="McNeill" />
* Poor maintenance of air conditioning systems has led to outbreaks of ''[[Legionella pneumophila]]''.<ref>{{cite web |url=https://www.nlm.nih.gov/medlineplus/ency/article/000616.htm|title=Legionnaire disease|access-date=12 April 2015}}</ref>
* Poor maintenance of air conditioning systems has led to outbreaks of ''[[Legionella pneumophila]]''.<ref>{{cite web |url=https://www.nlm.nih.gov/medlineplus/ency/article/000616.htm|title=Legionnaire disease|access-date=12 April 2015}}</ref>
* Hospital-acquired airborne diseases are associated with poorly-resourced and maintained medical systems,<ref>{{cite web |title=Hospital infection control: reducing airborne pathogens - Maintenance and Operations |url=https://www.healthcarefacilitiestoday.com/posts/Hospital-infection-control-reducing-airborne-pathogens--5523 |website=Healthcare Facilities Today |access-date=13 June 2022 |language=en}}</ref> which make [[Isolation (health care)|isolation]] challenging.{{citation needed|date=March 2020}}
* Hospital-acquired airborne diseases are associated with poorly-resourced and maintained medical systems.<ref>{{cite web |title=Hospital infection control: reducing airborne pathogens - Maintenance and Operations |url=https://www.healthcarefacilitiestoday.com/posts/Hospital-infection-control-reducing-airborne-pathogens--5523 |website=Healthcare Facilities Today |access-date=13 June 2022 |language=en}}</ref>
* Air conditioning may reduce transmission by removing contaminated air, but may also contribute to the spread of respiratory secretions inside a room.<ref name=":2" />
* Air conditioning may reduce transmission by removing contaminated air, but may also contribute to the spread of respiratory secretions inside a room.<ref name=":2" />
* The new findings reveal that understanding airflow patterns is even more crucial than simply increasing air changes per hour. During the COVID-19 pandemic, the common advice was to maximize ventilation, but this may not always be the most effective approach. A room can be well-prepared to prevent the spread of infectious diseases even at a low ACH. This insight could lead to safer building designs and significant energy savings during future pandemics.<ref>{{cite journal |last1=Zabihi |first1=Mojtaba |last2=Li |first2=Ri |last3=Brinkerhoff |first3=Joshua |title=Influence of indoor airflow on airborne disease transmission in a classroom |journal=Building Simulation |date=1 March 2024 |volume=17 |issue=3 |pages=355–370 |doi=10.1007/s12273-023-1097-y |url=https://link.springer.com/article/10.1007/s12273-023-1097-y |language=en |issn=1996-8744}}</ref>


==Prevention==
==Prevention==
A layered risk-management approach to slowing the spread of a transmissible disease attempts to minimize risk through multiple layers of interventions. Each intervention has the potential to reduce risk. A layered approach can include interventions by individuals (e.g. mask wearing, hand hygiene), institutions (e.g. surface disinfection, ventilation, and air filtration measures to control the indoor environment), the medical system (e.g. vaccination) and public health at the population level (e.g. testing, quarantine, and contact tracing).<ref name="McNeill"/>
A layered risk-management approach to slowing the spread of a transmissible disease attempts to minimize risk through multiple layers of interventions. Each intervention has the potential to reduce risk. A layered approach can include interventions by individuals (e.g. mask wearing, hand hygiene), institutions (e.g. surface disinfection, ventilation, and air filtration measures to control the indoor environment), the medical system (e.g. vaccination) and public health at the population level (e.g. testing, quarantine, and contact tracing).<ref name="McNeill"/>


Preventive techniques can include disease-specific [[immunization]] as well as nonpharmaceutical interventions such as wearing a [[respirator]] and limiting time spent in the presence of infected individuals.<ref name="Bloodborne and Airborne Pathogens">{{cite book |last=American Academy of Orthopaedic Surgeons (AAOS) |year=2011 |publisher=Jones & Barlett Publishers |pages=2 |url=https://books.google.com/books?id=8hbEOpBtBJIC&q=books+airborne+disease |title=Bloodborne and Airborne Pathogens |access-date=21 May 2013|isbn=9781449668273 }}</ref> Wearing a face mask can lower the risk of airborne transmission to the extent that it limits the transfer of airborne particles between individuals.<ref>{{cite journal | vauthors = Clark RP, de Calcina-Goff ML | title = Some aspects of the airborne transmission of infection | journal = Journal of the Royal Society, Interface | volume = 6 Suppl 6 | issue = suppl_6 | pages = S767-82 | date = December 2009 | pmid = 19815574 | pmc = 2843950 | doi = 10.1098/rsif.2009.0236.focus | url = }}</ref> The type of mask that is effective against airborne transmission is dependent on the size of the particles. While fluid-resistant surgical masks prevent large droplet inhalation, smaller particles which form aerosols require a higher level of protection with filtration masks rated at [[N95 respirator|N95]] (US) or [[FFP3]] (EU) required.<ref>{{Cite web|date=2020-02-06|title=Transmission-Based Precautions {{!}} Basics {{!}} Infection Control {{!}} CDC|url=https://www.cdc.gov/infectioncontrol/basics/transmission-based-precautions.html|access-date=2021-10-14|website=www.cdc.gov|language=en-us}}</ref> Use of FFP3 masks by staff managing patients with [[COVID-19]] reduced acquisition of COVID-19 by staff members.<ref>{{Cite journal|last1=Ferris|first1=Mark|last2=Ferris|first2=Rebecca|last3=Workman|first3=Chris|last4=O'Connor|first4=Eoin|last5=Enoch|first5=David A|last6=Goldesgeyme|first6=Emma|last7=Quinnell|first7=Natalie|last8=Patel|first8=Parth|last9=Wright|first9=Jo|last10=Martell|first10=Geraldine|last11=Moody|first11=Christine|date=2021-06-24|title=FFP3 respirators protect healthcare workers against infection with SARS-CoV-2|url=https://www.authorea.com/users/421653/articles/527590-ffp3-respirators-protect-healthcare-workers-against-infection-with-sars-cov-2?commit=e567e67501cd6ee0dd1a6e8e4acdf2c4fd70e0ec|doi=10.22541/au.162454911.17263721/v1}}</ref>
Preventive techniques can include disease-specific [[immunization]] as well as nonpharmaceutical interventions such as wearing a [[respirator]] and limiting time spent in the presence of infected individuals.<ref name="Bloodborne and Airborne Pathogens">{{cite book |last=American Academy of Orthopaedic Surgeons (AAOS) |year=2011 |publisher=Jones & Barlett Publishers |pages=2 |url=https://books.google.com/books?id=8hbEOpBtBJIC&q=books+airborne+disease |title=Bloodborne and Airborne Pathogens |access-date=21 May 2013|isbn=9781449668273 }}</ref> Wearing a face mask can lower the risk of airborne transmission to the extent that it limits the transfer of airborne particles between individuals.<ref>{{cite journal | vauthors = Clark RP, de Calcina-Goff ML | title = Some aspects of the airborne transmission of infection | journal = Journal of the Royal Society, Interface | volume = 6 | issue = suppl_6 | pages = S767–S782 | date = December 2009 | pmid = 19815574 | pmc = 2843950 | doi = 10.1098/rsif.2009.0236.focus }}</ref> The type of mask that is effective against airborne transmission is dependent on the size of the particles. While fluid-resistant surgical masks prevent large droplet inhalation, smaller particles which form aerosols require a higher level of protection with filtration masks rated at [[N95 respirator|N95]] (US) or [[FFP3]] (EU) required.<ref>{{Cite web|date=2020-02-06|title=Transmission-Based Precautions {{!}} Basics {{!}} Infection Control {{!}} CDC|url=https://www.cdc.gov/infectioncontrol/basics/transmission-based-precautions.html|access-date=2021-10-14|website=www.cdc.gov|language=en-us}}</ref> Use of FFP3 masks by staff managing patients with [[COVID-19]] reduced acquisition of COVID-19 by staff members.<ref>{{Cite journal | vauthors = Ferris M, Ferris R, Workman C, O'Connor E, Enoch DA, Goldesgeyme E, Quinnell N, Patel P, Wright J, Martell G, Moody C | display-authors = 6 | title = FFP3 respirators protect healthcare workers against infection with SARS-CoV-2. | journal = Authorea Preprints | date = June 2021 | url = https://www.authorea.com/users/421653/articles/527590-ffp3-respirators-protect-healthcare-workers-against-infection-with-sars-cov-2?commit=e567e67501cd6ee0dd1a6e8e4acdf2c4fd70e0ec | doi = 10.22541/au.162454911.17263721/v1 }}</ref>


[[Engineering controls|Engineering solutions]] which aim to control or eliminate exposure to a hazard are higher on the [[Hierarchy of hazard controls|hierarchy of control]] than [[personal protective equipment]] (PPE). At the level of physically based engineering interventions, effective ventilation and high frequency air changes, or air filtration through [[HEPA|high efficiency particulate filters]], reduce detectable levels of virus and other [[bioaerosol]]s, improving conditions for everyone in an area.<ref name="McNeill"/><ref name="Conway Morris ciab933">{{Cite journal|last1=Conway Morris|first1=Andrew|last2=Sharrocks|first2=Katherine|last3=Bousfield|first3=Rachel|last4=Kermack|first4=Leanne|last5=Maes|first5=Mailis|last6=Higginson|first6=Ellen|last7=Forrest|first7=Sally|last8=Pereira-Dias|first8=Joana|last9=Cormie|first9=Claire|last10=Old|first10=Tim|last11=Brooks|first11=Sophie|date=2021-10-30|title=The removal of airborne SARS-CoV-2 and other microbial bioaerosols by air filtration on COVID-19 surge units|journal=Clinical Infectious Diseases|language=en|pages=ciab933|doi=10.1093/cid/ciab933|pmid=34718446 |pmc=8689842 |issn=1058-4838}}</ref> Portable air filters, such as those tested in Conway Morris A et al. present a readily deployable solution when existing ventilation is inadequate, for instance in repurposed COVID-19 hospital facilities.<ref name="Conway Morris ciab933"/>
[[Engineering controls|Engineering solutions]] which aim to control or eliminate exposure to a hazard are higher on the [[Hierarchy of hazard controls|hierarchy of control]] than [[personal protective equipment]] (PPE). At the level of physically based engineering interventions, effective ventilation and high frequency air changes, or air filtration through [[HEPA|high efficiency particulate filters]], reduce detectable levels of virus and other [[bioaerosol]]s, improving conditions for everyone in an area.<ref>{{cite journal |last1=Zabihi |first1=Mojtaba |last2=Li |first2=Ri |last3=Brinkerhoff |first3=Joshua |title=Influence of indoor airflow on airborne disease transmission in a classroom |journal=Building Simulation |date=1 March 2024 |volume=17 |issue=3 |pages=355–370 |doi=10.1007/s12273-023-1097-y |url=https://link.springer.com/article/10.1007/s12273-023-1097-y |language=en |issn=1996-8744}}</ref><ref name="McNeill"/><ref name="Conway Morris ciab933">{{cite journal | vauthors = Conway Morris A, Sharrocks K, Bousfield R, Kermack L, Maes M, Higginson E, Forrest S, Pereira-Dias J, Cormie C, Old T, Brooks S, Hamed I, Koenig A, Turner A, White P, Floto RA, Dougan G, Gkrania-Klotsas E, Gouliouris T, Baker S, Navapurkar V | display-authors = 6 | title = The Removal of Airborne Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Other Microbial Bioaerosols by Air Filtration on Coronavirus Disease 2019 (COVID-19) Surge Units | journal = Clinical Infectious Diseases | volume = 75 | issue = 1 | pages = e97–e101 | date = August 2022 | pmid = 34718446 | pmc = 8689842 | doi = 10.1093/cid/ciab933 }}</ref> Portable air filters, such as those tested in Conway Morris A et al. present a readily deployable solution when existing ventilation is inadequate, for instance in repurposed COVID-19 hospital facilities.<ref name="Conway Morris ciab933"/>


The [[United States Centers for Disease Control and Prevention]] (CDC) advises the public about [[vaccination]] and following careful hygiene and sanitation protocols for airborne disease prevention.<ref>{{cite web|url=https://www.cdc.gov/vaccines/vpd-vac/|title=Redirect - Vaccines: VPD-VAC/VPD menu page|date=2019-02-07}}</ref> Many public health specialists recommend physical distancing (also known as [[social distancing]]) to reduce transmission.<ref name="pmid17283616">{{cite journal | vauthors = Glass RJ, Glass LM, Beyeler WE, Min HJ | title = Targeted social distancing design for pandemic influenza | journal = Emerging Infectious Diseases | volume = 12 | issue = 11 | pages = 1671–81 | date = November 2006 | pmid = 17283616 | pmc = 3372334 | doi = 10.3201/eid1211.060255 }}</ref>
The [[United States Centers for Disease Control and Prevention]] (CDC) advises the public about [[vaccination]] and following careful hygiene and sanitation protocols for airborne disease prevention.<ref>{{cite web|url=https://www.cdc.gov/vaccines/vpd-vac/|title=Redirect - Vaccines: VPD-VAC/VPD menu page|date=2019-02-07}}</ref> Many public health specialists recommend physical distancing (also known as [[social distancing]]) to reduce transmission.<ref name="pmid17283616">{{cite journal | vauthors = Glass RJ, Glass LM, Beyeler WE, Min HJ | title = Targeted social distancing design for pandemic influenza | journal = Emerging Infectious Diseases | volume = 12 | issue = 11 | pages = 1671–1681 | date = November 2006 | pmid = 17283616 | pmc = 3372334 | doi = 10.3201/eid1211.060255 }}</ref>


A 2011 study concluded that [[vuvuzela]]s (a type of air horn popular e.g. with fans at football games) presented a particularly high risk of airborne transmission, as they were spreading a much higher number of aerosol particles than e.g., the act of shouting.<ref name=":02">{{cite journal | vauthors = Lai KM, Bottomley C, McNerney R | title = Propagation of respiratory aerosols by the vuvuzela | journal = PLOS ONE | volume = 6 | issue = 5 | pages = e20086 | date = 2011-05-23 | pmid = 21629778 | pmc = 3100331 | doi = 10.1371/journal.pone.0020086 | bibcode = 2011PLoSO...620086L | doi-access = free }}</ref>
A 2011 study concluded that [[vuvuzela]]s (a type of air horn popular e.g. with fans at football games) presented a particularly high risk of airborne transmission, as they were spreading a much higher number of aerosol particles than e.g., the act of shouting.<ref name=":02">{{cite journal | vauthors = Lai KM, Bottomley C, McNerney R | title = Propagation of respiratory aerosols by the vuvuzela | journal = PLOS ONE | volume = 6 | issue = 5 | pages = e20086 | date = 2011-05-23 | pmid = 21629778 | pmc = 3100331 | doi = 10.1371/journal.pone.0020086 | doi-access = free | bibcode = 2011PLoSO...620086L }}</ref>


Exposure does not guarantee infection. The generation of aerosols, adequate transport of aerosols through the air, inhalation by a susceptible host, and deposition in the respiratory tract are all important factors contributing to the over-all risk for infection. Furthermore, the infective ability of the virus must be maintained throughout all these stages.<ref>{{Cite journal |last=Wang |first=Chia C. |last2=Prather |first2=Kimberly A. |last3=Sznitman |first3=Josué |last4=Jimenez |first4=Jose L. |last5=Lakdawala |first5=Seema S. |last6=Tufekci |first6=Zeynep |last7=Marr |first7=Linsey C. |date=2021-08-27 |title=Airborne transmission of respiratory viruses |url=https://www.science.org/doi/10.1126/science.abd9149 |journal=Science |language=en |volume=373 |issue=6558 |pages=eabd9149 |doi=10.1126/science.abd9149 |issn=0036-8075 |pmc=PMC8721651 |pmid=34446582}}</ref> In addition the risk for infection is also dependent on host [[immune system]] competency plus the quantity of infectious particles ingested.<ref name="Bloodborne and Airborne Pathogens"/>
Exposure does not guarantee infection. The generation of aerosols, adequate transport of aerosols through the air, inhalation by a susceptible host, and deposition in the respiratory tract are all important factors contributing to the over-all risk for infection. Furthermore, the infective ability of the virus must be maintained throughout all these stages.<ref>{{cite journal | vauthors = Wang CC, Prather KA, Sznitman J, Jimenez JL, Lakdawala SS, Tufekci Z, Marr LC | title = Airborne transmission of respiratory viruses | journal = Science | volume = 373 | issue = 6558 | pages = eabd9149 | date = August 2021 | pmid = 34446582 | pmc = 8721651 | doi = 10.1126/science.abd9149 }}</ref> In addition the risk for infection is also dependent on host [[immune system]] competency plus the quantity of infectious particles ingested.<ref name="Bloodborne and Airborne Pathogens"/>
[[Antibiotic]]s may be used in dealing with airborne bacterial primary infections, such as [[pneumonic plague]].<ref name="Prevent and Control Infection">{{cite book | vauthors = Ziady LE, Small N |title=Prevent and Control Infection: Application Made Easy |year=2006 |publisher=Juta and Company Ltd. |pages=119–120 |url=https://books.google.com/books?id=kSKwP3v99dYC&pg=PA119|isbn=9780702167904 }}</ref>
[[Antibiotic]]s may be used in dealing with airborne bacterial primary infections, such as [[pneumonic plague]].<ref name="Prevent and Control Infection">{{cite book | vauthors = Ziady LE, Small N |title=Prevent and Control Infection: Application Made Easy |year=2006 |publisher=Juta and Company Ltd. |pages=119–120 |url=https://books.google.com/books?id=kSKwP3v99dYC&pg=PA119|isbn=9780702167904 }}</ref>


Latest revision as of 21:54, 17 December 2024

Infected people generate larger droplets and aerosols which can infect over longer distances

A red poster with illustrations and the text: "AIRBORNE PRECAUTIONS. EVERYONE MUST: Clean their hands, including before entering and when leaving the room. Put on a fit-tested N-95 or higher level respirator before room entry. Remove respirator after exiting the room and closing the door. Door to room must remain closed."
A poster outlining precautions for airborne transmission in healthcare settings. It is intended to be posted outside rooms of patients with an infection that can spread through airborne transmission.[1]
Video explainer on reducing airborne pathogen transmission indoors

Airborne transmission or aerosol transmission is transmission of an infectious disease through small particles suspended in the air.[2] Infectious diseases capable of airborne transmission include many of considerable importance both in human and veterinary medicine. The relevant infectious agent may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, flushing toilets, or any activities which generate aerosol particles or droplets.

Infectious aerosols: physical terminology

[edit]

Aerosol transmission has traditionally been considered distinct from transmission by droplets, but this distinction is no longer used.[3][4] Respiratory droplets were thought to rapidly fall to the ground after emission:[5] but smaller droplets and aerosols also contain live infectious agents, and can remain in the air longer and travel farther.[4][6][7] Individuals generate aerosols and droplets across a wide range of sizes and concentrations, and the amount produced varies widely by person and activity.[8] Larger droplets greater than 100 μm usually settle within 2 m.[8][5] Smaller particles can carry airborne pathogens for extended periods of time. While the concentration of airborne pathogens is greater within 2m, they can travel farther and concentrate in a room.[4]

The traditional size cutoff of 5 μm between airborne and respiratory droplets has been discarded, as exhaled particles form a continuum of sizes whose fates depend on environmental conditions in addition to their initial sizes. This error has informed hospital based transmission based precautions for decades.[8] Indoor respiratory secretion transfer data suggest that droplets/aerosols in the 20 μm size range initially travel with the air flow from cough jets and air conditioning like aerosols,[9] but fall out gravitationally at a greater distance as "jet riders".[9] As this size range is most efficiently filtered out in the nasal mucosa,[10] the primordial infection site in COVID-19, aerosols/droplets[11] in this size range may contribute to driving the COVID-19 pandemic.

Overview

[edit]

Airborne diseases can be transmitted from one individual to another through the air. The pathogens transmitted may be any kind of microbe, and they may be spread in aerosols, dust or droplets. The aerosols might be generated from sources of infection such as the bodily secretions of an infected individual, or biological wastes. Infectious aerosols may stay suspended in air currents long enough to travel for considerable distances; sneezes, for example, can easily project infectious droplets for dozens of feet (ten or more meters).[12]

Airborne pathogens or allergens typically enter the body via the nose, throat, sinuses and lungs. Inhalation of these pathogens affects the respiratory system and can then spread to the rest of the body. Sinus congestion, coughing and sore throats are examples of inflammation of the upper respiratory airway. Air pollution plays a significant role in airborne diseases. Pollutants can influence lung function by increasing air way inflammation.[13]

Common infections that spread by airborne transmission include SARS-CoV-2;[14] measles morbillivirus,[15] chickenpox virus;[16] Mycobacterium tuberculosis, influenza virus, enterovirus, norovirus and less commonly other species of coronavirus, adenovirus, and possibly respiratory syncytial virus.[17] Some pathogens which have more than one mode of transmission are also anisotropic, meaning that their different modes of transmission can cause different kinds of diseases, with different levels of severity. Two examples are the bacterias Yersinia pestis (which causes plague) and Francisella tularensis (which causes tularaemia), which both can cause severe pneumonia, if transmitted via the airborne route through inhalation.[18]

Poor ventilation enhances transmission by allowing aerosols to spread undisturbed in an indoor space.[19] Crowded rooms are more likely to contain an infected person. The longer a susceptible person stays in such a space, the greater chance of transmission. Airborne transmission is complex, and hard to demonstrate unequivocally[20] but the Wells-Riley model can be used to make simple estimates of infection probability.[21]

Some airborne diseases can affect non-humans. For example, Newcastle disease is an avian disease that affects many types of domestic poultry worldwide that is airborne. Poultry animals are often also airborne.[22]

It has been suggested that airborne transmission should be classified as being either obligate, preferential, or opportunistic, although there is limited research that show the importance of each of these categories.[23] Obligate airborne infections spread only through aerosols; the most common example of this category is tuberculosis. Preferential airborne infections, such as chicken pox, can be obtained through different routes, but mainly by aerosols. Opportunistic airborne infections such as influenza typically transmit through other routes; however, under favourable conditions, aerosol transmission can occur.[24]

Transmission efficiency

[edit]

Environmental factors influence the efficacy of airborne disease transmission; the most evident environmental conditions are temperature and relative humidity.[25][26] The transmission of airborne diseases is affected by all the factors that influence temperature and humidity, in both meteorological (outdoor) and human (indoor) environments. Circumstances influencing the spread of droplets containing infectious particles can include pH, salinity, wind, air pollution, and solar radiation as well as human behavior.[27]

Airborne infections usually land in the respiratory system, with the agent present in aerosols (infectious particles < 5 μm in diameter).[28] This includes dry particles, often the remnant of an evaporated wet particle called nuclei, and wet particles.

  • Relative humidity (RH) plays an important role in the evaporation of droplets and the distance they travel. 30 μm droplets evaporate in seconds.[29] The CDC recommends a minimum of 40% RH indoors[30] to significantly reduce the infectivity of aerosolized virus. An ideal humidity for preventing aerosol respiratory viral transmission at room temperature appears to be between 40% and 60% RH. If the relative humidity goes below 35% RH, infectious virus stays longer in the air.
  • The number of rainy days[31] (more important than total precipitation);[32][33] mean daily sunshine hours;[34] latitude and altitude[32] are relevant when assessing the possibility of spread of airborne disease. Some infrequent or exceptional events influence the dissemination of airborne diseases, including tropical storms, hurricanes, typhoons, or monsoons.[35]
  • Climate affects temperature, winds and relative humidity, the main factors affecting the spread, duration and infectiousness of droplets containing infectious particles.[25] The influenza virus spreads easily in the Northern Hemisphere winter due to climate conditions that favour the infectiousness of the virus.[27]
  • Isolated weather events decrease the concentration of airborne fungal spores; a few days later, number of spores increases exponentially.[36]
  • Socioeconomics has a minor role in airborne disease transmission. In cities, airborne disease spreads more rapidly than in rural areas and urban outskirts. Rural areas generally favor higher airborne fungal dissemination.[37]
  • Proximity to large bodies of water such as rivers and lakes can enhance airborne disease.[35]
  • A direct association between insufficient ventilation rates and increased COVID-19 transmission has been observed. Prior to COVID-19, standards for ventilation systems focused more on supplying sufficient oxygen to a room, rather than disease-related aspects of air quality.[4]
  • Poor maintenance of air conditioning systems has led to outbreaks of Legionella pneumophila.[38]
  • Hospital-acquired airborne diseases are associated with poorly-resourced and maintained medical systems.[39]
  • Air conditioning may reduce transmission by removing contaminated air, but may also contribute to the spread of respiratory secretions inside a room.[9]
  • The new findings reveal that understanding airflow patterns is even more crucial than simply increasing air changes per hour. During the COVID-19 pandemic, the common advice was to maximize ventilation, but this may not always be the most effective approach. A room can be well-prepared to prevent the spread of infectious diseases even at a low ACH. This insight could lead to safer building designs and significant energy savings during future pandemics.[40]

Prevention

[edit]

A layered risk-management approach to slowing the spread of a transmissible disease attempts to minimize risk through multiple layers of interventions. Each intervention has the potential to reduce risk. A layered approach can include interventions by individuals (e.g. mask wearing, hand hygiene), institutions (e.g. surface disinfection, ventilation, and air filtration measures to control the indoor environment), the medical system (e.g. vaccination) and public health at the population level (e.g. testing, quarantine, and contact tracing).[4]

Preventive techniques can include disease-specific immunization as well as nonpharmaceutical interventions such as wearing a respirator and limiting time spent in the presence of infected individuals.[41] Wearing a face mask can lower the risk of airborne transmission to the extent that it limits the transfer of airborne particles between individuals.[42] The type of mask that is effective against airborne transmission is dependent on the size of the particles. While fluid-resistant surgical masks prevent large droplet inhalation, smaller particles which form aerosols require a higher level of protection with filtration masks rated at N95 (US) or FFP3 (EU) required.[43] Use of FFP3 masks by staff managing patients with COVID-19 reduced acquisition of COVID-19 by staff members.[44]

Engineering solutions which aim to control or eliminate exposure to a hazard are higher on the hierarchy of control than personal protective equipment (PPE). At the level of physically based engineering interventions, effective ventilation and high frequency air changes, or air filtration through high efficiency particulate filters, reduce detectable levels of virus and other bioaerosols, improving conditions for everyone in an area.[45][4][46] Portable air filters, such as those tested in Conway Morris A et al. present a readily deployable solution when existing ventilation is inadequate, for instance in repurposed COVID-19 hospital facilities.[46]

The United States Centers for Disease Control and Prevention (CDC) advises the public about vaccination and following careful hygiene and sanitation protocols for airborne disease prevention.[47] Many public health specialists recommend physical distancing (also known as social distancing) to reduce transmission.[48]

A 2011 study concluded that vuvuzelas (a type of air horn popular e.g. with fans at football games) presented a particularly high risk of airborne transmission, as they were spreading a much higher number of aerosol particles than e.g., the act of shouting.[49]

Exposure does not guarantee infection. The generation of aerosols, adequate transport of aerosols through the air, inhalation by a susceptible host, and deposition in the respiratory tract are all important factors contributing to the over-all risk for infection. Furthermore, the infective ability of the virus must be maintained throughout all these stages.[50] In addition the risk for infection is also dependent on host immune system competency plus the quantity of infectious particles ingested.[41] Antibiotics may be used in dealing with airborne bacterial primary infections, such as pneumonic plague.[51]

See also

[edit]

References

[edit]
  1. ^ "Transmission-Based Precautions". U.S. Centers for Disease Control and Prevention. 7 January 2016. Retrieved 31 March 2020.
  2. ^ Siegel JD, Rhinehart E, Jackson M, Chiarello L, Healthcare Infection Control Practices Advisory Committee. "2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings" (PDF). CDC. p. 19. Retrieved 7 February 2019. Airborne transmission occurs by dissemination of either airborne droplet nuclei or small particles in the respirable size range containing infectious agents that remain infective over time and distance
  3. ^ Tang JW, Marr LC, Li Y, Dancer SJ (April 2021). "Covid-19 has redefined airborne transmission". BMJ. 373: n913. doi:10.1136/bmj.n913. PMID 33853842. S2CID 233235666.
  4. ^ a b c d e f McNeill VF (June 2022). "Airborne Transmission of SARS-CoV-2: Evidence and Implications for Engineering Controls". Annual Review of Chemical and Biomolecular Engineering. 13 (1): 123–140. doi:10.1146/annurev-chembioeng-092220-111631. PMID 35300517. S2CID 247520571.
  5. ^ a b Zhang N, Chen W, Chan PT, Yen HL, Tang JW, Li Y (July 2020). "Close contact behavior in indoor environment and transmission of respiratory infection". Indoor Air. 30 (4): 645–661. Bibcode:2020InAir..30..645Z. doi:10.1111/ina.12673. PMID 32259319. S2CID 215408351.
  6. ^ Pal A, Biswas R, Pal R, Sarkar S, Mukhopadhyay A (1 January 2023). "A novel approach to preventing SARS-CoV-2 transmission in classrooms: A numerical study". Physics of Fluids. 35 (1): 013308. doi:10.1063/5.0131672. ISSN 1070-6631. S2CID 254779734.
  7. ^ Biswas R, Pal A, Pal R, Sarkar S, Mukhopadhyay A (January 2022). "Risk assessment of COVID infection by respiratory droplets from cough for various ventilation scenarios inside an elevator: An OpenFOAM-based computational fluid dynamics analysis". Physics of Fluids. 34 (1): 013318. arXiv:2109.12841. Bibcode:2022PhFl...34a3318B. doi:10.1063/5.0073694. PMC 8939552. PMID 35340680.
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  40. ^ Zabihi, Mojtaba; Li, Ri; Brinkerhoff, Joshua (1 March 2024). "Influence of indoor airflow on airborne disease transmission in a classroom". Building Simulation. 17 (3): 355–370. doi:10.1007/s12273-023-1097-y. ISSN 1996-8744.
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  44. ^ Ferris M, Ferris R, Workman C, O'Connor E, Enoch DA, Goldesgeyme E, et al. (June 2021). "FFP3 respirators protect healthcare workers against infection with SARS-CoV-2". Authorea Preprints. doi:10.22541/au.162454911.17263721/v1.
  45. ^ Zabihi, Mojtaba; Li, Ri; Brinkerhoff, Joshua (1 March 2024). "Influence of indoor airflow on airborne disease transmission in a classroom". Building Simulation. 17 (3): 355–370. doi:10.1007/s12273-023-1097-y. ISSN 1996-8744.
  46. ^ a b Conway Morris A, Sharrocks K, Bousfield R, Kermack L, Maes M, Higginson E, et al. (August 2022). "The Removal of Airborne Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Other Microbial Bioaerosols by Air Filtration on Coronavirus Disease 2019 (COVID-19) Surge Units". Clinical Infectious Diseases. 75 (1): e97–e101. doi:10.1093/cid/ciab933. PMC 8689842. PMID 34718446.
  47. ^ "Redirect - Vaccines: VPD-VAC/VPD menu page". 7 February 2019.
  48. ^ Glass RJ, Glass LM, Beyeler WE, Min HJ (November 2006). "Targeted social distancing design for pandemic influenza". Emerging Infectious Diseases. 12 (11): 1671–1681. doi:10.3201/eid1211.060255. PMC 3372334. PMID 17283616.
  49. ^ Lai KM, Bottomley C, McNerney R (23 May 2011). "Propagation of respiratory aerosols by the vuvuzela". PLOS ONE. 6 (5): e20086. Bibcode:2011PLoSO...620086L. doi:10.1371/journal.pone.0020086. PMC 3100331. PMID 21629778.
  50. ^ Wang CC, Prather KA, Sznitman J, Jimenez JL, Lakdawala SS, Tufekci Z, Marr LC (August 2021). "Airborne transmission of respiratory viruses". Science. 373 (6558): eabd9149. doi:10.1126/science.abd9149. PMC 8721651. PMID 34446582.
  51. ^ Ziady LE, Small N (2006). Prevent and Control Infection: Application Made Easy. Juta and Company Ltd. pp. 119–120. ISBN 9780702167904.
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