CDC Revising Isolation Guidelines; Revisiting Airborne, Droplet Spread
Dropping ponderous document for condensed approach
Infection prevention leaders welcomed the Centers for Disease Control and Prevention’s (CDC) plan to revise its 2007 patient isolation guideline, which will include dropping the current 206-page “textbook” approach for a leaner, more user-friendly document that healthcare workers can easily access and understand.1
The plan was announced at a March 24, 2022, meeting of the CDC’s Healthcare Infection Control Practices Advisory Committee (HICPAC). Attending the virtual event was Linda Dickey, RN, MPH, CIC, FAPIC, president of the Association for Professionals in Infection Control and Epidemiology (APIC).
“Based on what was described, a more condensed structure for the guidance will be helpful,” she tells Hospital Infection Control & Prevention (HIC). “Anything to make it easier for users of the information to more effectively find what they’re looking for and provide clarity in the intent is useful and, I believe, would be welcomed by infection preventionists.”
With that in mind, the first part of the revised guidelines, which will include the gamut of isolation precautions, will be a 10- to 15-page document that can be accessed in PDF form on a mobile device.
“This will provide an updated scientific foundation for how pathogens spread in the healthcare setting,” said Michael Lin, MD, MPH, co-chair of the HICPAC isolation work group. The goal is to have the concise “new part one” document in draft form for the committee’s meeting this November.
Sections of established science and specific issues, such as needle reuse, from the 2007 document will not be discarded, but may be repackaged into other documents or included to some degree in the next iteration of the isolation revision process (i.e., “new part two”), said Michael Bell, MD, deputy director of the CDC Division of Healthcare Quality Promotion.
“We will not throw any of that away,” he said at the HICPAC meeting. “But we are deliberately trying to make this a much leaner and cleaner document. This is intended to provide the framework for a lot of subsequent products. This first piece of work is a hard intellectual lift to get us to the point as a nation where we can agree on a new framework. Then we will move forward with how we implement it.”
Connie Steed, RN, a former APIC president who is now an infection prevention consultant in Greenville, SC, is a member of the HICPAC workgroup on the isolation revision.
“There will be places where there will be the detail that some people desire, but the key is to simplify it so that it is easier to understand and digest,” she says.
Droplet vs. Airborne
A major focus of the revision of the isolation guidelines will be on delineating the blurred line between droplet and airborne precautions, which has been the subject of some confusion and controversy during the pandemic. The conventional wisdom has been that most respiratory infections spread primarily by larger droplets at short-range, but there is a new appreciation of a wide variation in particle sizes and the importance of good ventilation and air exchange.
“Since the publication of the [2007] isolation guideline, new evidence has emerged regarding the size of pathogen [particle] transmission in the healthcare setting,” said Lin, associate professor of infectious diseases at Rush University Medical Center in Chicago. “For example, and probably most importantly, the distinction between droplet and airborne routes of respiratory transmission needs to be reevaluated.”
Traditionally, under respiratory droplet precautions, masks should be worn by healthcare workers and, if possible, by the patient for source control to prevent spread within a three- to six-foot range. Established airborne pathogens, such as measles and tuberculosis, call for N95 respirators and a negative pressure isolation rooms to prevent spread throughout a facility via air currents.
“There is much that needs to be analyzed regarding droplet and airborne transmission with COVID-19,” Dickey says. “HICPAC’s work to carefully look at evidence and provide updated guidance will be tremendously beneficial. For example, we may see the emergence of more nuanced precautions [for] COVID-19 regarding the wearing of N-95 respirators and targeted use of airborne infection isolation rooms.”
The issue of airborne spread of COVID-19, with the exception of aerosol-producing procedures, has been somewhat contentious, recalling similar debates when SARS-CoV-1 struck in 2002-2003. The CDC reported last year that emerging science shows transmission of SARS-CoV-2 airborne viral particles can occur beyond six feet, particularly in enclosed, poorly ventilated spaces. This risk increases in “enclosed spaces with inadequate ventilation or air handling within which the concentration of exhaled respiratory fluids, especially very fine droplets and aerosol particles, can build up in the air space,” the CDC emphasized.2
“This is probably one of the most important things that will be discussed as the workgroup goes through this process,” Steed says. “Because of COVID-19, there is now a lot of gray between droplet and airborne transmission. There will be a lot of discussion on the modes of transmission to bring some clarity to this.”
Linsey Marr, PhD, professor of civil and environmental engineering at Virginia Tech in Blacksburg, VA, researches viral particle movement in the air.
“I think there is bias in favor of droplet precautions because they’re easier and cheaper, and because airborne transmission has been defined to occur at long range, which you don’t see much in a well-ventilated hospital,” she tells HIC. “In fact, inhalation of the virus at short range, in close proximity to an infected person, is probably the most frequent route of transmission.”
The first task of the HICPAC workgroup will be a review of the literature, and there is no dearth of studies on this issue since the pandemic began. In its aforementioned 2021 scientific brief, the CDC cited many of them in concluding, “Although infections through inhalation at distances greater than six feet from an infectious source are less likely than at closer distances, the phenomenon has been repeatedly documented under certain preventable circumstances.”3-6
The Biden administration cited the CDC brief in pushing for new initiatives to improve indoor air quality at schools and workplaces at a March 29, 2022, meeting led by Alondra Nelson, PhD, director of the White House Office of Science and Technology Policy.
“I want to be very clear, COVID-19 is transmitted through the air,” she said. “Bringing more clean air into a room reduces airborne disease transmission and reduces COVID-19 transmission. For example, having five air changes per hour can reduce transmission risk by 50% or more.”
Marr also spoke at the White House meeting, emphasizing that improving air ventilation and using high-efficiency particulate air filter (HEPA) machines can greatly reduce risk of transmission.
“If you have great ventilation, you can reduce the amount of virus that is in the air by a factor of five — maybe even a factor of 10,” Marr said at the meeting. “And that is going to reduce everyone’s individual risk. We are all breathing all the time. We can’t avoid it. We are all sharing the air. This is why ventilation has such great potential to help us with reducing the risk of transmission of COVID and other respiratory diseases.”
In a related development, the Occupational Safety and Health Administration (OSHA) now is in the process of finalizing its Emergency Temporary Standard (ETS) to protect healthcare workers from COVID-19. (See “OSHA Finalizing COVID-19 Rule in Healthcare Settings.”)
The OSHA ETS included technical requirements on ventilation, calling for heating, ventilation, and air conditioning (HVAC) systems to be used in accordance with the manufacturer’s instructions and design specifications for the systems. Air filters must be rated Minimum Efficiency Reporting Value (MERV) 13 or higher if the system allows it. “If MERV-13 or higher filters are not compatible with the HVAC system(s), employers must use filters with the highest compatible filtering efficiency for the HVAC system(s),” the OSHA ETS noted. This section also requires that “all air filters are maintained and replaced as necessary to ensure the proper function and performance of the HVAC system(s); and all intake ports that provide outside air to the HVAC system(s) are cleaned, maintained, and cleared of any debris that may affect the function.”7
WHO Finally Goes Airborne
Public health officials, including the World Health Organization (WHO), were reluctant to describe SARS-CoV-2 as an airborne virus when the pandemic began. Much was unknown — much is still unknown — about the pandemic virus, and the WHO wanted definitive evidence before it spurred public fear at a time when there was no vaccine or defined treatment. The changes to WHO guidance were incremental after that, as the organization gathered the information that would be needed to undo its strong initial stance against airborne transmission. Finally, the WHO conceded “airborne” spread was among the modes of transmission when it updated its website on Dec. 23, 2021.8
By then, studies on the pandemic virus showed spread in singing choirs and poorly ventilated restaurants. Air engineering scientists warned of this possibility early on, but it conflicted with accepted medical “dogma,” says Gabor Lantos, PEng, MBA, MD, president of Occupational Health Management Services in Toronto. “Infectious diseases literature only very rarely intersects with the physical science literature.”
One historically underappreciated element is the varying particle sizes that can carry virus, he adds. Larger droplets come from the mouth and nasopharynx, intermediate sizes from the bronchi or bronchioles, and tiny aerosol particles from the alveoli, he explains.
“Cut-off sizes are purely arbitrary,” Lantos says. “The distances [particles] can travel and the time they can remain airborne — suspended — depends on size and velocity. [Other factors] include normal exhalation, singing, coughing, sneezing, and on ambient conditions, such as temperature, humidity, airflow, air turbulence, and barometric pressure.”
A veteran infection preventionist and former member of HICPAC confirmed that established assumptions about particle sizes led to some errors in thinking about COVID-19. “[For] droplet and airborne, we thought particles are one size. Well, no, they’re not,” said Ruth Carrico, PhD, FSHEA, RN, CIC, a professor of infectious disease at the University of Louisville. “Airborne is not only small [particles], and droplet is not only large. When someone coughs, they project a variety of particle sizes. This really hit home with this coronavirus — that we could have many different sizes of particles.”
As a result of this realization, infectious disease experts are moving away from “compartmentalizing” isolation and thinking more broadly about how disease is transmitted, she said at a recent APIC webinar.
“Some [larger particles] will fall out of circulation and contaminate the environment — that’s why we need to be thinking about environmental disinfection,” Carrico said. “Some will be smaller in size and may actually follow air current.”
Healthcare workers must use personal protective equipment, including eye protection, to avoid contact with these various particle sizes, along with respiratory protection to avoid inhaling the very small particles that may be aerosolized, she concluded.
REFERENCES
- Siegel JD, Rhinehart E, Jackson M, et al. 2007 guideline for isolation precautions: Preventing transmission of infectious agents in healthcare settings. Centers for Disease Control and Prevention. https://www.cdc.gov/niosh/docket/archive/pdfs/niosh-219/0219-010107-siegel.pdf
- Centers for Disease Control and Prevention. Scientific brief: SARS-CoV-2 transmission. Updated May 7, 2021. https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/sars-cov-2-transmission.html
- Groves LM, Usagawa L, Elm J, et al. Community transmission of SARS-CoV-2 at three fitness facilities — Hawaii, June-July 2020. MMWR Morb Mortal Wkly Rep 2021;70:316-320.
- Hamner L, Dubbel P, Capron I, et al. High SARS-CoV-2 attack rate following exposure at a choir practice – Skagit County, Washington, March 2020. MMWR Morb Mortal Wkly Rep 2020;69:606-610.
- Li Y, Qian H, Hang J, et al. Probable airborne transmission of SARS-CoV-2 in a poorly ventilated restaurant. Build Environ 2021;196:107788.
- Katelaris AL, Wells J, Clark P, et al. Epidemiologic evidence for airborne transmission of SARS-CoV-2 during church singing, Australia, 2020. Emerg Infect Dis 2021;27:1677-1680.
- Occupational Safety and Health Administration. Subpart U — COVID-19 Emergency Temporary Standard. https://www.osha.gov/sites/default/files/covid-19-healthcare-ets-reg-text.pdf
- Lewis D. Why the WHO took two years to say COVID is airborne. Nature 2022;604:26-31.
Infection prevention leaders welcomed the CDC's plan to revise its 2007 patient isolation guideline, which will include dropping the current 206-page “textbook” approach for a leaner, more user-friendly document that healthcare workers can easily access and understand.
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