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Source control (respiratory disease)

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This article is about the strategy for reducing disease transmission. For the sepsis management strategy, see Sepsis § Source control. For other uses, see Source control (disambiguation).
Source control is recommended for members of the general public during severe epidemics, especially in crowded indoor areas such as stores.
In hospitals, proper source control protocols are essential.

Source control is a strategy for reducing disease transmission by blocking respiratory secretions produced through breathing,[1] speaking, coughing, sneezing[2] or singing.[3] Multiple source control techniques can be used in hospitals,[4] but for the general public wearing personal protective equipment during epidemics or pandemics, respirators provide the greatest source control,[1] 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.[5][6][7]

Mechanisms[edit]

Droplet spread without source control: up to ~8 meters (26 ft) for sneezes and coughs, up to ~2 meters (6.6 ft) for talking. Aerosol spread is much further than this.[8]

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.[9]

Coughs and sneezes can spread airborne droplets up to ~8 meters (26 ft). Speaking can spread droplets up to ~2 meters (6.6 ft).[8]

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.[7]

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.[8]

Contrast with personal protective equipment[edit]

Masks with exhalation valves are not very effective for source control. However, some respirators with exhalation valves performed as well a surgical mask in source control. Respirators without exhalation valves should be preferred.[1]

While source control protects others from transmission arising from the wearer, personal protective equipment protects the wearer themselves.[10] Cloth face masks can be used for source control (as a last resort) but are not considered personal protective equipment[2][10] as they have low filter efficiency (generally varying between 2–60%), although they are easy to obtain and reusable after washing.[11] There are no standards or regulation for self-made cloth face masks,[12] and source control on a well-fitted cloth mask is worse than a surgical mask.[6]

Surgical masks are designed to protect against splashes and sprays,[5] 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.[13] Surgical masks are regulated by various national standards to have high bacterial filtration efficiency (BFE).[14][15][16] However, source control is less than that of a respirator without an exhalation valve.[1] 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.[5][1]

Comparison of face masks by function
Type Source control Inhaled air filtration Ref
Cloth face mask Worse than surgical Bad [2][10][6]
Surgical mask or procedure mask Some Less than respirator Bad [5][13][1]
Respirator without exhalation valve Good Good [5]
Respirator with unfiltered exhalation valve Some Depends on respirator Good [5][1]
Respirator with filtered exhalation valve Good Good [5]

Source Control during TB Outbreaks[edit]

US HIV/AIDS Epidemic[edit]

See also: N95 respirator § History, and Hierarchy of hazard controls
1997 proposed OSHA administrative rule: No Admittance Without Wearing a Type N95 or More Protective Respirator[17]
Similar to NIOSH's Hierarchy of Hazard Controls, multiple controls are used for source control of TB[18]
NIOSH guidelines for TB, with focus on respirators under the old 30 CFR 11, replaced in 1995

HIV was a noted co-infection in around 35% of those affected by TB in some regions of the US,[19] 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 a infected person's latent TB into active TB source.[4]

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.[20]

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,[20] but withdrew them in 2003 following the decline of TB.[21]

Engineering controls mainly involve ventilation and planning isolation rooms,[20] but can also involve environmental controls, like negative pressure, ultraviolet germicidal radiation, and the use of HEPA filters.[22]

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.[20]

During TB outbreaks in the 1990s, multiple hospitals upgraded their controls and policies to attenuate the spread of TB.[18]

COVID-19 pandemic[edit]

See also: Face masks during the COVID-19 pandemic

During the COVID-19 pandemic, cloth face masks for source control have been recommended by the U.S. Centers for Disease Control and Prevention (CDC) for members of the public who leave their homes, and health care facilities are commended to consider requiring face masks for all people who enter the facility. Health care personnel and patients with COVID-19 symptoms are recommended to use surgical masks if available, as they are more protective.[23] Masking patients reduces the personal protective equipment recommended by CDC for health care personnel under crisis shortage conditions.[24]

References[edit]

  1. ^ a b c d e f g Hazard, Jessica M.; Cappa, Christopher D. (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.
  2. ^ a b c "FAQs on the Emergency Use Authorization for Face Masks (Non-Surgical)". U.S. Food and Drug Administration. 2020-04-26. Retrieved 2020-05-21.
  3. ^ Naunheim, Matthew R.; Bock, Jonathan; Doucette, Philip A.; Hoch, Matthew; Howell, Ian; Johns, Michael M.; Johnson, Aaron M.; Krishna, Priya; Meyer, David; Milstein, Claudio F.; Nix, John (2020-06-28). "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. ISSN 0892-1997. PMC 7330568. PMID 32753296.
  4. ^ a b "Basics of Tuberculosis.". Tuberculosis in the Workplace. National Academies Press (US). 2001.
  5. ^ a b c d e f g "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. 2020-05-18. Retrieved 2020-05-21.
  6. ^ a b c Koh, Xue Qi; Sng, Anqi; Chee, Jing Yee; Sadovoy, Anton; Luo, Ping; Daniel, Dan (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.
  7. ^ a b Hunziker, Patrick (2020-12-16). "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.
  8. ^ a b c Sommerstein, R; Fux, CA; Vuichard-Gysin, D; Abbas, M; Marschall, J; Balmelli, C; Troillet, N; Harbarth, S; Schlegel, M; Widmer, A; Swissnoso. (6 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. ISSN 2047-2994. PMC 7336106. PMID 32631450.
  9. ^ Carbone, Michele; Lednicky, John; Xiao, Shu-Yuan; Venditti, Mario; Bucci, Enrico (2021). "Coronavirus 2019 Infectious Disease Epidemic: Where We Are, What Can be Done and Hope for". Journal of Thoracic Oncology. 16 (Carbone M, Lednicky J, Xiao SY, Venditti M, Bucci E. Coronavirus 2019 Infectious Disease Epidemic: Where We Are, What Can Be Done and Hope For. J Thorac Oncol. 2021 Apr, 16(4):546-571. doi: 10.1016/j.jtho.2020.12.014. Epub 2021 Jan 7. PMID 33422679, PMCID: PMC7832772): 546–571. doi:10.1016/j.jtho.2020.12.014. PMC 7832772. PMID 33422679.
  10. ^ 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. 2020-05-12. At section "Cloth face coverings in meat and poultry processing facilities". Retrieved 2020-05-24.
  11. ^ Rengasamy S, Eimer B, Shaffer RE (2010). "Simple Respiratory Protection—Evaluation of the Filtration Performance of Cloth Masks and Common Fabric Materials Against 20–1000 nm Size Particles". Annals of Occupational Hygiene. 54 (7). Oxford University Press: 789–798. doi:10.1093/annhyg/meq044. ISSN 0003-4878. 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.
  12. ^ "Community Respirators and Masks". NIOSH. 21 June 2023. Retrieved 2024-06-22.
  13. ^ a b "N95 Respirators and Surgical Masks (Face Masks)". U.S. Food and Drug Administration. 2020-04-05. Retrieved 2020-05-23.
  14. ^ Robertson, Paddy (15 March 2020). "Comparison of Mask Standards, Ratings, and Filtration Effectiveness". Smart Air Filters.
  15. ^ 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)
  16. ^ 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 2021-02-25 at the Wayback Machine (in Chinese)
  17. ^ "DEPARTMENT OF LABOR Occupational Safety and Health Administration 29 CFR Part 1910 [Docket No. H-371] RIN 1218-AB46 Occupational Exposure to Tuberculosis".
  18. ^ a b "Implementation and Effects of CDC Guidelines". Tuberculosis in the Workplace. National Academies Press (US). 2001.
  19. ^ "Introduction". Tuberculosis in the Workplace. National Academies Press (US). 2001.
  20. ^ a b c d "Comparison of CDC Guidelines and Proposed OSHA Rule". Tuberculosis in the Workplace. National Academies Press (US). 2001.
  21. ^ "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".
  22. ^ Lee, Ji Yeon (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.
  23. ^ "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. 2020-05-18. Retrieved 2020-05-21.
  24. ^ "Strategies for Optimizing the Supply of N95 Respirators". U.S. Centers for Disease Control and Prevention. 2020-04-02. At section "Prioritize the use of N95 respirators and facemasks by activity type". Retrieved 2020-05-21.
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