Source control (respiratory disease)

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Certified respirators, without exhalation valves, are the recommended form of source control. 200318-H-NI589-069 (49679050543).jpg
Certified respirators, without exhalation valves, are the recommended form of source control.
In hospitals, proper source control protocols are essential. 200401-N-PH222-1033 (49743455427).jpg
In hospitals, proper source control protocols are essential.

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.

Contents

Mechanisms

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. Droplet transmission ranges for speaking, intubation, and coughing or sneezing.jpg
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.

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. [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

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

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

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

Before 42 CFR 84 N95s, powered air-purifying respirators were the recommended form of PPE for healthcare. However, they provide poor source control should the worker be infected. (Read on Wikisource) Halfmask PAPR drawing page 45.png
Before 42 CFR 84 N95s, powered air-purifying respirators were the recommended form of PPE for healthcare. However, they provide poor source control should the worker be infected.
(Read 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]

Comparison of face masks by function
TypeSource controlInhaled air filtrationRef
Cloth face mask Dark Red x.svg Worse than surgicalDark Red x.svg Bad [12] [11] [15]
Surgical mask or procedure maskAvoid if possibleDark Red x.svg Bad [16] [17] [10] [7]
Respirator without exhalation valveGreen check.svg GoodGreen check.svg Good [16]
Respirator with unfiltered exhalation valveBrown check.svg Depends on respiratorGreen check.svg Good [16] [10]
Respirator with filtered exhalation valveGreen check.svg GoodGreen check.svg Good [16]

Source Control during TB Outbreaks

US HIV/AIDS epidemic

1997 proposed OSHA administrative rule: No Admittance Without Wearing a Type N95 or More Protective Respirator N95 stop.svg
1997 proposed OSHA administrative rule: No Admittance Without Wearing a Type N95 or More Protective Respirator
Similar to NIOSH's Hierarchy of Hazard Controls, multiple controls are used for source control of TB NIOSH's "Hierarchy of Controls infographic" as SVG.svg
Similar to NIOSH's Hierarchy of Hazard Controls, multiple controls are used for source control of TB
NIOSH guidelines for TB, with focus on respirators under the old 30 CFR 11, replaced in 1995 (On Wikisource) Niosh tb guidelines.pdf
NIOSH guidelines for TB, with focus on respirators under the old 30 CFR 11, replaced in 1995 (On Wikisource)

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 a 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

United States

HICPAC 2007 Guideline for Isolation Precautions. A more general guideline for hospital PPE procedures. (PDF, 225 pages) 2007 Guidelines for Isolation Precautions.pdf
HICPAC 2007 Guideline for Isolation Precautions. A more general guideline for hospital PPE procedures. (PDF, 225 pages)

Pre-COVID

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]

However, separate from "barrier precautions" and "standard precautions" are "airborne precautions", a specific 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 should be used whenever someone is suspected of harboring an "infectious agent". [36] [37]

Early measures

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

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. [lower-alpha 1] 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

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 a 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

Notes

Related Research Articles

<span class="mw-page-title-main">Personal protective equipment</span> Equipment designed to help protect an individual from hazards

Personal protective equipment (PPE) is protective clothing, helmets, goggles, or other garments or equipment designed to protect the wearer's body from injury or infection. The hazards addressed by protective equipment include physical, electrical, heat, chemical, biohazards, and airborne particulate matter. Protective equipment may be worn for job-related occupational safety and health purposes, as well as for sports and other recreational activities. Protective clothing is applied to traditional categories of clothing, and protective gear applies to items such as pads, guards, shields, or masks, and others. PPE suits can be similar in appearance to a cleanroom suit.

<span class="mw-page-title-main">Surgical mask</span> Mouth and nose cover against bacterial aerosols

A surgical mask, also known by other names such as a medical face mask or procedure mask, is a personal protective equipment used by healthcare professionals that serves as a mechanical barrier that interferes with direct airflow in and out of respiratory orifices. This helps reduce airborne transmission of pathogens and other aerosolized contaminants between the wearer and nearby people via respiratory droplets ejected when sneezing, coughing, forceful expiration or unintentionally spitting when talking, etc. Surgical masks may be labeled as surgical, isolation, dental or medical procedure masks.

<span class="mw-page-title-main">Respirator</span> Device worn to protect the user from inhaling contaminants

A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including lead fumes, vapors, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories of respirators: the air-purifying respirator, in which respirable air is obtained by filtering a contaminated atmosphere, and the air-supplied respirator, in which an alternate supply of breathable air is delivered. Within each category, different techniques are employed to reduce or eliminate noxious airborne contaminants.

<span class="mw-page-title-main">Isolation (health care)</span> Measure taken to prevent contagious diseases from being spread

In health care facilities, isolation represents one of several measures that can be taken to implement in infection control: the prevention of communicable diseases from being transmitted from a patient to other patients, health care workers, and visitors, or from outsiders to a particular patient. Various forms of isolation exist, in some of which contact procedures are modified, and others in which the patient is kept away from all other people. In a system devised, and periodically revised, by the U.S. Centers for Disease Control and Prevention (CDC), various levels of patient isolation comprise application of one or more formally described "precaution".

<span class="mw-page-title-main">Airborne transmission</span> Disease transmission by airborne particles

Airborne transmission or aerosol transmission is transmission of an infectious disease through small particles suspended in the air. 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.

Transmission-based precautions are infection-control precautions in health care, in addition to the so-called "standard precautions". They are the latest routine infection prevention and control practices applied for patients who are known or suspected to be infected or colonized with infectious agents, including certain epidemiologically important pathogens, which require additional control measures to effectively prevent transmission. Universal precautions are also important to address as far as transmission-based precautions. Universal precautions is the practice of treating all bodily fluids as if it is infected with HIV, HBV, or other blood borne pathogens.

<span class="mw-page-title-main">Wells curve</span> Science of medicine

The Wells curve is a diagram, developed by W. F. Wells in 1934, which describes what is expected to happen to small droplets once they have been exhaled into air. Coughing, sneezing, and other violent exhalations produce high numbers of respiratory droplets derived from saliva and/or respiratory mucus, with sizes ranging from about 1 μm to 2 mm. Wells' insight was that such droplets would have two distinct fates, depending on their sizes. The interplay of gravity and evaporation means that droplets larger than a humidity-determined threshold size would fall to the ground due to gravity, while droplets smaller than this size would quickly evaporate, leaving a dry residue that drifts in the air. Since droplets from an infected person may contain infectious bacteria or viruses, these processes influence transmission of respiratory diseases.

<span class="mw-page-title-main">Respiratory droplet</span> Type of particle formed by breathing

A respiratory droplet is a small aqueous droplet produced by exhalation, consisting of saliva or mucus and other matter derived from respiratory tract surfaces. Respiratory droplets are produced naturally as a result of breathing, speaking, sneezing, coughing, or vomiting, so they are always present in our breath, but speaking and coughing increase their number.

<span class="mw-page-title-main">NIOSH air filtration rating</span> U.S. rating of respirators

The NIOSH air filtration rating is the U.S. National Institute for Occupational Safety and Health (NIOSH)'s classification of filtering respirators. The ratings describe the ability of the device to protect the wearer from solid and liquid particulates in the air. The certification and approval process for respiratory protective devices is governed by Part 84 of Title 42 of the Code of Federal Regulations. Respiratory protective devices so classified include air-purifying respirators (APR) such as filtering facepiece respirators and chemical protective cartridges that have incorporated particulate filter elements.

<span class="mw-page-title-main">Powered air-purifying respirator</span> Full-face respirator that provides filtered air to the wearer using an electric fan

A powered air-purifying respirator (PAPR) is a type of respirator used to safeguard workers against contaminated air. PAPRs consist of a headgear-and-fan assembly that takes ambient air contaminated with one or more type of pollutant or pathogen, actively removes (filters) a sufficient proportion of these hazards, and then delivers the clean air to the user's face or mouth and nose. They have a higher assigned protection factor than filtering facepiece respirators such as N95 masks. PAPRs are sometimes called positive-pressure masks, blower units, or just blowers.

<span class="mw-page-title-main">N95 respirator</span> Particulate respirator meeting the N95 standard

An N95 respirator is a disposable filtering facepiece respirator or reusable elastomeric respirator filter that meets the U.S. National Institute for Occupational Safety and Health (NIOSH) N95 standard of air filtration, filtering at least 95% of airborne particles that have a mass median aerodynamic diameter of 0.3 micrometers under 42 CFR 84, effective July 10, 1995. A surgical N95 is also rated against fluids, and is regulated by the US Food and Drug Administration under 21 CFR 878.4040, in addition to NIOSH 42 CFR 84. 42 CFR 84, the federal standard which the N95 is part of, was created to address shortcomings in the prior United States Bureau of Mines respirator testing standards, as well as tuberculosis outbreaks, caused by the HIV/AIDS epidemic in the United States. Since then, N95 respirator has continued to be solidified as a source control measure in various pandemics that have been experienced in the United States and Canada, including the 2009 swine flu and the COVID-19 pandemic.

<span class="mw-page-title-main">Workplace hazard controls for COVID-19</span> Prevention measures for COVID-19

Hazard controls for COVID-19 in workplaces are the application of occupational safety and health methodologies for hazard controls to the prevention of COVID-19. Multiple layers of controls are recommended, including measures such as remote work and flextime, personal protective equipment (PPE) and face coverings, social distancing, and enhanced cleaning programs. Recently, engineering controls have been emphasized, particularly stressing the importance of HVAC systems meeting a minimum of 5 air changes per hour with ventilation or MERV-13 filters, as well as the installation of UVGI systems in public areas.

<span class="mw-page-title-main">Cloth face mask</span> Mask made of common textiles worn over the mouth and nose

A cloth face mask is a mask made of common textiles, usually cotton, worn over the mouth and nose. When more effective masks are not available, and when physical distancing is impossible, cloth face masks are recommended by public health agencies for disease "source control" in epidemic situations to protect others from virus laden droplets in infected mask wearers' breath, coughs, and sneezes. Because they are less effective than N95 masks, surgical masks, or physical distancing in protecting the wearer against viruses, they are not considered to be personal protective equipment by public health agencies.

An aerosol-generating procedure (AGP) is a medical or health-care procedure that a public health agency such as the World Health Organization or the United States Centers for Disease Control and Prevention (CDC) has designated as creating an increased risk of transmission of an aerosol borne contagious disease, such as COVID-19. The presumption is that the risk of transmission of the contagious disease from a patient having an AGP performed on them is higher than for a patient who is not having an AGP performed upon them. This then informs decisions on infection control, such as what personal protective equipment (PPE) is required by a healthcare worker performing the medical procedure, or what PPE healthcare workers are allowed to use.

<span class="mw-page-title-main">Mechanical filter (respirator)</span> Air-filtering face masks or mask attachments

Mechanical filters, a part of particulate respirators, are a class of filter for air-purifying respirators that mechanically stops particulates from reaching the wearer's nose and mouth. They come in multiple physical forms.

<span class="mw-page-title-main">Face masks during the COVID-19 pandemic</span> Health control procedure against COVID-19

During the COVID-19 pandemic, face masks or coverings, including N95, FFP2, surgical, and cloth masks, have been employed as public and personal health control measures against the spread of SARS-CoV-2, the virus that causes COVID-19.

In epidemiology, a non-pharmaceutical intervention (NPI) is any method used to reduce the spread of an epidemic disease without requiring pharmaceutical drug treatments. Examples of non-pharmaceutical interventions that reduce the spread of infectious diseases include wearing a face mask and staying away from sick people.

<span class="mw-page-title-main">Transmission of COVID-19</span> Mechanisms that spread coronavirus disease 2019

The transmission of COVID-19 is the passing of coronavirus disease 2019 from person to person. COVID-19 is mainly transmitted when people breathe in air contaminated by droplets/aerosols and small airborne particles containing the virus. Infected people exhale those particles as they breathe, talk, cough, sneeze, or sing. Transmission is more likely the closer people are. However, infection can occur over longer distances, particularly indoors.

<span class="mw-page-title-main">Elastomeric respirator</span> Respirator with a rubber face seal

Elastomeric respirators, also called reusable air-purifying respirators, seal to the face with elastomeric material, which may be a natural or synthetic rubber. They are generally reusable. Full-face versions of elastomeric respirators seal better and protect the eyes.

The European respirator standards refer to the filtering classification by EN 149, EN 14683, and EN 143, all European standards of testing and marking requirements for respirators. FFP standard masks cover the nose, mouth and chin and may have inhalation and/or exhalation valves.

References

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