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Source control is a strategy for reducing disease transmission by blocking respiratory secretions produced through breathing, speaking, coughing, sneezing or singing.[1] Multiple source control techniques can be used in hospitals, but for the general public wearing personal protective equipment during epidemics or pandemics, respirators provide the greatest source control, followed by surgical masks, with cloth face masks recommended for use by the public only when there are shortages of both respirators and surgical masks.
Mechanisms
[edit]
Infections in general may spread by direct contact (for example, shaking hands or kissing), by inhaling infectious droplets in the air (droplet transmission), by inhaling long-lasting aerosols with tiny particles (airborne transmission), and by touching objects with infectious material on their surfaces (fomites). Different diseases spread in different ways; some spread by only some of these routes. For instance, fomite transmission of COVID-19 is thought to be rare while aerosol, droplet and contact transmission appear to be the primary transmission modes, as of April 2021[update].[3]
Coughs and sneezes can spread airborne droplets up to ~8 meters (26 ft). Speaking can spread droplets up to ~2 meters (6.6 ft).[2]
Masking any person who may be a source of infectious droplets (or aerosols) thus reduces the unsafe range of physical distances. If a person can be infectious before they are symptomatic and diagnosed, then people who do not yet know if they are infectious may also be a source of infection.
For pathogens transmitted through the air, strategies to block cough air jets and to capture aerosols, e.g. the "Shield & Sink" approach, can be highly effective in minimizing exposure to respiratory secretions.[4]
Outside of respiratory source control, handwashing helps to protect people against contact transmission, and against indirect droplet transmission. Handwashing removes infectious droplets that their mask caught (from either side) and which transferred to their hands when they touched their mask.[2]
Potentially ineffective methods of source control
[edit]In the past, suggestions have been made that covering the mouth and nose, like with an elbow, tissue, or hand, would be a viable measure towards reducing the transmissions of airborne diseases. This method of source control was suggested, but not empirically tested, in the "Control of Airborne Infection" section of a 1974 publication of Riley's Airborne Infection.[5] NIOSH also noted that the use of a tissue as source control, in their guidelines for TB, had not been tested as of 1992.[6]
In 2013, Gustavo et al. looked into the effectiveness of various methods of source control, including via the arm, via a tissue, via bare hands, and via a surgical mask. They concluded that simply covering a cough was not an effective method of stopping transmission, and a surgical mask was not effective at reducing the amount of displaced droplets detected compared to the other rudimentary forms of source control.[7] Another paper noted that the fit of a face mask matters in its source control performance.[8] (However, note that OSHA 29 CFR 1910.134 does not cover the fit of face masks other than NIOSH-approved respirators.[9])
Contrast with personal protective equipment
[edit]
While source control protects others from transmission arising from the wearer, personal protective equipment protects the wearer themselves.[11] Cloth face masks can be used for source control (as a last resort) but are not considered personal protective equipment[12][11] as they have low filter efficiency (generally varying between 2–60%), although they are easy to obtain and reusable after washing.[13] There are no standards or regulation for self-made cloth face masks,[14] and source control on a well-fitted cloth mask is worse than a surgical mask.[15]
Surgical masks are designed to protect against splashes and sprays,[16] but do not provide complete respiratory protection from germs and other contaminants because of the loose fit between the surface of the face mask and the face.[17] Surgical masks are regulated by various national standards to have high bacterial filtration efficiency (BFE).[18][19][20] N95/N99/N100 masks and other filtering facepiece respirators can provide source control in addition to respiratory protection, but respirators with an unfiltered exhalation valve may not provide source control and require additional measures to filter exhalation air when source control is required.[16][10]
Exhalation source control with respirators
[edit](Script on Wikisource)
Some masks have exhalation valve that let the exhaled air go out unfiltered. The certification grade of the mask (such as N95) is about the mask itself and it does not warrant any safety about the air that is expelled by the wearer through the valve. A mask with valve mainly increases the comfort of the wearer.[21]
Unfiltered exhalation of air is found on both filtering facepiece and elastomeric respirators with exhalation valves.[21] Unfiltered air is also found on powered air-purifying respirators, which cannot ever filter exhaled air.[22] During the COVID-19 pandemic, masks with unfiltered-exhalation valves ran counter to the requirements of some mandatory mask orders.[23][24] Despite the aforementioned belief, a 2020 research by the NIOSH and CDC shows that an uncovered exhalation valve already provides source control on a level similar to, or even better than, surgical masks.[25][10]
It is possible to seal some unfiltered exhalation valves[26] or to cover it with an additional surgical mask; this might be done where mask shortages make it necessary.[27][28] However, so long as there are no shortages, respirators without exhalation valves should still be preferred in situations where source control is necessary.[10]
| Type | Source control | Inhaled air filtration | Ref |
|---|---|---|---|
| Cloth face mask |  Worse than surgical |
Bad
|
[12][11][15] |
| Surgical mask or procedure mask | Avoid if possible | Bad
|
[16][17][10][7] |
| Respirator without exhalation valve |  Good |
Good
|
[16] |
| Respirator with unfiltered exhalation valve |  Depends on respirator |
Good
|
[16][10] |
| Respirator with filtered exhalation valve | Good |
Good
|
[16] |
Source Control during TB Outbreaks
[edit] | The examples and perspective in this section may not represent a worldwide view of the subject. (June 2024) |
US HIV/AIDS epidemic
[edit]
HIV was a noted co-infection in around 35% of those affected by TB in some regions of the US,[31] despite extended close contact being a requisite factor for infection. Respirable particles are noted to be created by handling TB-infected tissue, or by coughing by those actively infected. Once in the air, droplet nuclei can persist in unventilated spaces. Most people infected with TB are asymptomatic, unless the immune system is weakened by some other factor, like HIV/AIDS, which can turn an infected person's latent TB into active TB source.[32]
1994 CDC guidelines brought three methods of source control for the prevention of TB: administrative controls, engineering controls, and personal protective equipment, particularly with the use of fit-checked respirators.[33]
Administrative controls mainly involve people and areas in hospital responsible for TB controls, including training, skin-testing, and regulatory compliance, as well as those responsible for quantifying the amount of TB present in the hospital's community and in-hospital, like staff. To assist with this, OSHA proposed TB guidelines in 1997,[33] but withdrew them in 2003 following the decline of TB.[34]
Engineering controls mainly involve ventilation and planning isolation rooms,[33] but can also involve environmental controls, like negative pressure, ultraviolet germicidal radiation, and the use of HEPA filters.[35]
The use of personal protective equipment, in this system of TB controls, requires the use of respirators whenever personnel are in contact with someone suspected of having TB, including during transport. This includes anyone near the infected person, all of whom must be provided with some sort of personal protective equipment, to avoid contracting TB. If PPE cannot be provided in time, the infected patient should be delayed from being moved through an area not controlled by PPE until the controls are in place, unless the care of the infected patient is compromised by an administrative delay.[33]
During TB outbreaks in the 1990s, multiple hospitals upgraded their controls and policies to attenuate the spread of TB.[30]
COVID-19 pandemic
[edit]United States
[edit]
Pre-COVID
[edit]In 2007, the CDC HICPAC published a set of guidelines, called the 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings, suggesting that use of "barrier precautions", defined as "masks, gowns, [and] gloves", would not be required, so long as it was limited to "routine entry", patients were not confirmed to be infected, and no aerosol-generating procedures were being done. "Standard precautions" requiring the use of masks, face shields, and/or eye protection, would be needed if there was potential for the spraying of bodily fluids, like during intubation.[36][37]
The guidelines are the same regardless of the type of pathogen, but the guidelines also note that, based on the experience of SARS-CoV in Toronto, that "N95 or higher respirators may offer additional protection to those exposed to aerosol-generating procedures and high risk activities".[36]
Separate from "barrier precautions" and "standard precautions" are "airborne precautions", a protocol for "infectious agents transmitted by the airborne route", like with SARS-CoV and tuberculosis, requiring 12 air changes per hour for new facilities, and use of fitted N95 respirators. These measures are used whenever someone is suspected of harboring an "infectious agent".[36][37]
Early measures
[edit]During the COVID-19 pandemic, cloth face masks for source control had been recommended by the U.S. Centers for Disease Control and Prevention (CDC) for members of the public who left their homes, and health care facilities were recommended to consider requiring face masks for all people who enter a facility. Health care personnel and patients with COVID-19 symptoms were recommended to use surgical masks if available, as they are more protective.[38] Masking patients reduces the personal protective equipment recommended by CDC for health care personnel under crisis shortage conditions.[39]
Post-2023
[edit]By 2023, The New York Times noted that the CDC had dropped mandates for masks in hospitals during COVID, limiting the COVID policies to an advisory role. Use of masks for source control is still recommended in times of high viral activity, but the CDC did not provide numbers for benchmarks. The new policies are thought, according to the New York Times, based on various citations to medical literature, to increase mortality among vulnerable patients, especially those with cancer.[40]
The New York Times article cites a paper published in 2023, that suggests the high mortality of cancer patients following the Omicron wave may have been due to relaxing of policies preventing COVID-19 transmission[41] (like source control policies). The 2023 paper also cites a research letter published in 2022, that suggests that the surge of COVID-19 cases in hospitals may have been due to the high contagiousness of Omicron,[42] an article which suggested a high secondary attack rate relative to Delta,[43] and papers finding increased mortality of cancer patients due to higher rates of breakthrough infections.[44][45]
Also in 2023, new draft guidelines were proposed by the CDC HICPAC, to update the pre-COVID 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings.[a] The proposed updates were met with disapproval by the National Nurses United union, as they felt the changes did not go far enough.[40] Changes included clarifying by adding "source control" as a qualification for the use of "barrier precautions".[46]
United Kingdom
[edit]A paper in the Journal of Hospital Infection, published in 2024, focusing on hospitals in the UK, found that the removal of mandates, based around surgical masks, in hospitals was not associated with an increase in SARS-CoV-2 infections from weeks between December 4, 2021 to December 10, 2022. However, the authors noted that the end of mask mandates also coincided with an increase in Omicron infections, and that more data would be needed despite evidence for removal of mask mandates from 2022-2023.[47]
See also
[edit]- Face masks during the COVID-19 pandemic
- N95 respirator
- Respirator assigned protection factors
- Workplace hazard controls for COVID-19
Notes
[edit]References
[edit]- ^ Naunheim MR, Bock J, Doucette PA, Hoch M, Howell I, Johns MM, et al. (September 2021). "Safer Singing During the SARS-CoV-2 Pandemic: What We Know and What We Don't". Journal of Voice. 35 (5): 765–771. doi:10.1016/j.jvoice.2020.06.028. PMC 7330568. PMID 32753296.
- ^ a b c Sommerstein R, Fux CA, Vuichard-Gysin D, Abbas M, Marschall J, Balmelli C, et al. (July 2020). "Risk of SARS-CoV-2 transmission by aerosols, the rational use of masks, and protection of healthcare workers from COVID-19". Antimicrobial Resistance and Infection Control. 9 (1): 100. doi:10.1186/s13756-020-00763-0. PMC 7336106. PMID 32631450.
- ^ Carbone M, Lednicky J, Xiao SY, Venditti M, Bucci E (April 2021). "Coronavirus 2019 Infectious Disease Epidemic: Where We Are, What Can Be Done and Hope For". Journal of Thoracic Oncology. 16 (4): 546–571. doi:10.1016/j.jtho.2020.12.014. PMC 7832772. PMID 33422679.
- ^ Hunziker P (2025-08-06). "Minimizing exposure to respiratory droplets, 'jet riders' and aerosols in air-conditioned hospital rooms by a 'Shield-and-Sink' strategy". medRxiv 10.1101/2020.12.08.20233056v1.
- ^ Riley RL (1974). "Airborne infection". The American Journal of Medicine. 57 (3): 466–475. doi:10.1016/0002-9343(74)90140-5. PMID 4212915.
- ^ NIOSH Recommended Guidelines for Personal Respiratory Protection of Workers in Health-care Facilities Potentially Exposed to Tuberculosis. U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health. 1992. p. 12.
- ^ a b Zayas G, Chiang MC, Wong E, MacDonald F, Lange CF, Senthilselvan A, et al. (2013). "Effectiveness of cough etiquette maneuvers in disrupting the chain of transmission of infectious respiratory diseases". BMC Public Health. 13: 811. doi:10.1186/1471-2025-08-061. PMC 3846148. PMID 24010919.
- ^ Lindsley WG, Blachere FM, Beezhold DH, Law BF, Derk RC, Hettick JM, et al. (2021). "A comparison of performance metrics for cloth masks as source control devices for simulated cough and exhalation aerosols". Aerosol Science and Technology. 55 (10): 1125–1142. Bibcode:2021AerST..55.1125L. doi:10.1080/02786826.2021.1933377. PMC 9345405. PMID 35923216.
- ^ "1910.134 - Respiratory Protection". OSHA. Retrieved 2025-08-06.
- ^ a b c d e f Hazard JM, Cappa CD (June 2022). "Performance of Valved Respirators to Reduce Emission of Respiratory Particles Generated by Speaking". Environmental Science & Technology Letters. 9 (6): 557–560. Bibcode:2022EnSTL...9..557H. doi:10.1021/acs.estlett.2c00210. PMID 37552726.
- ^ a b c "Meat and Poultry Processing Workers and Employers: Interim Guidance from CDC and the Occupational Safety and Health Administration (OSHA)". Centers for Disease Control and Prevention. 2025-08-06. At section "Cloth face coverings in meat and poultry processing facilities". Retrieved 2025-08-06.
- ^ a b "FAQs on the Emergency Use Authorization for Face Masks (Non-Surgical)". U.S. Food and Drug Administration. 2025-08-06. Retrieved 2025-08-06.
- ^ Rengasamy S, Eimer B, Shaffer RE (October 2010). "Simple respiratory protection--evaluation of the filtration performance of cloth masks and common fabric materials against 20-1000 nm size particles". The Annals of Occupational Hygiene. 54 (7). Oxford University Press: 789–798. doi:10.1093/annhyg/meq044. PMC 7314261. PMID 20584862.
The results showed that cloth masks and other fabric materials tested in the study had 40–90% instantaneous penetration levels against polydisperse NaCl aerosols employed in the National Institute for Occupational Safety and Health particulate respirator test protocol at 5.5 cm s?1.
- ^ "Community Respirators and Masks". NIOSH. 21 June 2023. Retrieved 2025-08-06.
- ^ a b Koh XQ, Sng A, Chee JY, Sadovoy A, Luo P, Daniel D (February 2022). "Outward and inward protection efficiencies of different mask designs for different respiratory activities". Journal of Aerosol Science. 160. Bibcode:2022JAerS.16005905K. doi:10.1016/j.jaerosci.2021.105905.
- ^ a b c d e f "Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19) in Healthcare Settings". U.S. Centers for Disease Control and Prevention. 2025-08-06. Retrieved 2025-08-06.
- ^ a b "N95 Respirators and Surgical Masks (Face Masks)". U.S. Food and Drug Administration. 2025-08-06. Archived from the original on March 5, 2020. Retrieved 2025-08-06.
- ^ Robertson P (15 March 2020). "Comparison of Mask Standards, Ratings, and Filtration Effectiveness". Smart Air Filters.
- ^ 中华人民共和国医药行业标准：YY 0469–2011 医用外科口罩 (Surgical mask) (in Chinese)
- ^ 中华人民共和国医药行业标准：YY/T 0969–2013 一次性使用医用口罩 (Single-use medical face mask) Archived 2025-08-06 at the Wayback Machine (in Chinese)
- ^ a b "Coronavirus Disease 2019 (COVID-19)". Centers for Disease Control and Prevention. 11 February 2020. Archived from the original on 2025-08-06.
- ^ Institute of Medicine (2015). "Defining PAPRs and Current Standards". The Use and Effectiveness of Powered Air Purifying Respirators in Health Care: Workshop Summary. Washington, D.C.: National Academies Press. doi:10.17226/18990. ISBN 978-0-309-31595-1. PMID 25996018.
- ^ Wilson M (April 28, 2020). "What is a mask valve, and why are cities banning them?". MSN.
- ^ Webeck E (22 April 2020). "Coronavirus: Bay Area mask order takes effect Wednesday. Here's what you need to know". The Mercury News.
- ^ Portnoff L, Schall J, Brannen J, Suhon N, Strickland K, Meyers J (2020). "Filtering Facepiece Respirators with an Exhalation Valve: Measurements of Filtration Efficiency to Evaluate Their Potential for Source Control". DHHS (NIOSH) Publication No. 2021-107. National Institute for Occupational Safety and Health. doi:10.26616/NIOSHPUB2021107.
- ^ Filtering Facepiece Respirators with an Exhalation Valve: Measurements of Filtration Efficiency to Evaluate Their Potential for Source Control (Technical report). 30 June 2021. doi:10.26616/NIOSHPUB2021107. S2CID 235456824.
- ^ Liu D, Koo TH, Wong J, Wong YH, Fung K, Chan Y, et al. (August 2020). "Adapting re-usable elastomeric respirators to utilise anaesthesia circuit filters using a 3D-printed adaptor - a potential alternative to address N95 shortages during the COVID-19 pandemic". Anaesthesia. 75 (8): 1022–1027. doi:10.1111/anae.15108. PMC 7267584. PMID 32348561.
- ^ "San Antonio hospital could have an answer to the PPE crisis-- elastomeric masks". kens5.com. May 1, 2020.
But she added you can easily cover the mask with a surgical mask or shield.
- ^ "DEPARTMENT OF LABOR Occupational Safety and Health Administration 29 CFR Part 1910 [Docket No. H-371] RIN 1218-AB46 Occupational Exposure to Tuberculosis".
- ^ a b "Implementation and Effects of CDC Guidelines". Tuberculosis in the Workplace. National Academies Press (US). 2001.
- ^ "Introduction". Tuberculosis in the Workplace. National Academies Press (US). 2001.
- ^ "Basics of Tuberculosis.". Tuberculosis in the Workplace. National Academies Press (US). 2001.
- ^ a b c d "Comparison of CDC Guidelines and Proposed OSHA Rule". Tuberculosis in the Workplace. National Academies Press (US). 2001.
- ^ "Part III DEPARTMENT OF LABOR Occupational Safety and Health Administration 29 CFR Part 1910 [Docket No. H-371] RIN 1218-AB46 Occupational Exposure to Tuberculosis".
- ^ Lee JY (October 2016). "Tuberculosis Infection Control in Health-Care Facilities: Environmental Control and Personal Protection". Tuberculosis and Respiratory Diseases. 79 (4): 234–240. doi:10.4046/trd.2016.79.4.234. PMC 5077726. PMID 27790274.
- ^ a b c "2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings" (PDF).
- ^ a b "Hospital Respiratory Protection Program Toolkit" (PDF). OSHA. May 2015. Archived from the original (PDF) on 2025-08-06.
- ^ "Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19) in Healthcare Settings". U.S. Centers for Disease Control and Prevention. 2025-08-06. Retrieved 2025-08-06.
- ^ "Strategies for Optimizing the Supply of N95 Respirators". U.S. Centers for Disease Control and Prevention. 2025-08-06. At section "Prioritize the use of N95 respirators and facemasks by activity type". Retrieved 2025-08-06.
- ^ a b Mandavilli A (2025-08-06). "In Hospitals, Viruses Are Everywhere. Masks Are Not". New York Times. Retrieved 2025-08-06.
- ^ Potter AL, Vaddaraju V, Venkateswaran S, Mansur A, Bajaj SS, Kiang MV, et al. (October 2023). "Deaths Due to COVID-19 in Patients With Cancer During Different Waves of the Pandemic in the US". JAMA Oncology. 9 (10): 1417–1422. doi:10.1001/jamaoncol.2023.3066. PMID 37651113.
- ^ Klompas M, Pandolfi MC, Nisar AB, Baker MA, Rhee C (July 2022). "Association of Omicron vs Wild-type SARS-CoV-2 Variants With Hospital-Onset SARS-CoV-2 Infections in a US Regional Hospital System". Jama. 328 (3): 296–298. doi:10.1001/jama.2022.9609. PMC 9201738. PMID 35704347.
- ^ Lyngse FP, Mortensen LH, Denwood MJ, Christiansen LE, M?ller CH, Skov RL, et al. (September 2022). "Household transmission of the SARS-CoV-2 Omicron variant in Denmark". Nature Communications. 13 (1): 5573. Bibcode:2022NatCo..13.5573L. doi:10.1038/s41467-022-33328-3. PMID 36151099.
- ^ Gong IY, Vijenthira A, Powis M, Calzavara A, Patrikar A, Sutradhar R, et al. (March 2023). "Association of COVID-19 Vaccination With Breakthrough Infections and Complications in Patients With Cancer". JAMA Oncology. 9 (3): 386–394. doi:10.1001/jamaoncol.2022.6815. PMC 10020872. PMID 36580318.
- ^ Potter AL, Vaddaraju V, Venkateswaran S, Mansur A, Bajaj SS, Kiang MV, et al. (October 2023). "Deaths Due to COVID-19 in Patients With Cancer During Different Waves of the Pandemic in the US". JAMA Oncology. 9 (10): 1417–1422. doi:10.1001/jamaoncol.2023.3066. PMID 37651113.
- ^ "Proposed Update to Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings (2007), 'Protective Environment' Recommendation" (PDF). Archived from the original (PDF) on 2025-08-06.
- ^ Mehra R, Patterson B, Riley P, Planche T, Breathnach A (2024). "Impact of removing the healthcare mask mandate on hospital-acquired COVID-19 rates". Journal of Hospital Infection. 145: 59–64. doi:10.1016/j.jhin.2023.12.004. PMID 38141666.
Further reading
[edit]
- Chen CC, Willeke K (1992). "Aerosol penetration through surgical masks". American Journal of Infection Control. 20 (4): 177–184. doi:10.1016/S0196-6553(05)80143-9. PMID 1524265.
- Krishnan U, Janicak CA (1999). "Compliance with OSHA's Respiratory Protection Standard in Hospitals". American Industrial Hygiene Association Journal. 60 (2): 228–234. doi:10.1080/00028899908984440. PMID 10222573.
