CDC Draft Revamps Airborne Precautions, Calls for N95s
A new ‘continuum’ to stop transmission by air
New draft patient isolation guidelines recently approved by advisors to the Centers for Disease Control and Prevention (CDC) call for scrapping the “outdated dichotomy” of droplet/airborne precautions in favor of a “continuum” approach to stop transmission through the air.
“The draft 2024 guideline updates the conceptual framework, including the recognition of a continuum of pathogen transmission by air rather than an outdated dichotomy of droplet vs. airborne transmission.1 It proposes new categories for transmission-based precautions,” said Michael Lin, MD, MPH, co-chair of the isolation workgroup for the CDC’s Healthcare Infection Control Practices Advisory Committee (HICPAC).
The draft guidelines now go to the CDC for review and, if approved, they will be published in the Federal Register for a two-month comment period.
“Those comments will be taken into consideration for incorporation into the draft after further discussion by HICPAC and the final draft will come back for a vote in full,” said Michael Bell, MD, a CDC medical epidemiologist and liaison to the panel.
When the full document is completed — HICPAC approved one major section — it will replace the 2007 CDC isolation precautions.2 HICPAC voted to approve a draft of the new guidelines, which outline the general principles and recommendations to prevent transmission but does not list measures for individual pathogens. That is a work in progress, and at a previous meeting, Bell said it may take two years. In the interim, the committee recommended infection preventionists (IPs) refer to appendix A of the 2007 isolation precuations.3
When the COVID-19 pandemic began in 2020, the conventional wisdom was that most respiratory infections were spread primarily by larger droplets at short range, approximately three to six feet. However, it became increasingly clear in outbreak investigations that SARS-CoV-2 was spreading beyond that range and poor ventilation was a major contributing factor.4-6 The CDC reported in 2021 that emerging science shows transmission of SARS-CoV-2 airborne viral particles can occur beyond six feet, particularly in enclosed, poorly ventilated spaces.7
Moreover, the CDC held a “listening session” with experts a few weeks before the Nov. 6-7, 2023, HICPAC meeting, when the new draft guidelines were approved.
At the listening session, Donald Milton, MD, DrPH, professor of environmental health at the University of Maryland, said, according to the minutes of the meeting, “[It is] now widely recognized that the traditional notion that close proximity equals transmission via sprays of ballistic drops called ‘droplet transmission’ was wrong. Poor ventilation compounds the problem and extends it over larger distances.”8
Accordingly, the HICPAC draft guidelines reflect a new appreciation of the wide variation in particle sizes and airborne transmission over distances. In addition to calling for selective use of airborne infection isolation rooms (AIIRs) — which have negative air pressure relative to the outside hall and a higher rate of air exchanges — the HICPAC draft guidelines state, “[We] recognize the importance of interventions such as general ventilation with sufficient delivery rates of clean air to dilute pathogens in air, local exhaust ventilation to capture pathogens at their source, and removal of infective pathogens from air such as by filtration through portable HEPA [high-efficiency particulate air] filters or by inactivation via ultraviolet germicidal irradiation. An advantage of these interventions is that they do not require individual compliance to be effective.”
Three Tiers of Air Precautions
The draft guidelines have three tiers of air transmission precautions, two of which call for the use of N95 respirators.
“There is a new category for transmission through the air called Special Air Precautions, which is expected to increase the use of NIOSH [National Institute for Occupational Safety and Health]-approved, fit-tested N95 or higher level respirators during responses to pandemic or emerging respiratory [pathogens],” Lin said at the HICPAC meeting.
The approved draft air precautions are outlined as follows:
Routine Air Precautions: “[These] are focused on reducing transmission of common, often endemic, respiratory pathogens that spread predominantly over short distances based on observed patterns of transmission, and for which individuals and their communities are likely to have some degree of immunity,” the draft guidelines state.
• Healthcare personnel (HCP) should use a mask on room entry, and use eye protection based on standard precautions.
• Place the patient in a private room; if not available, then cohort.
• Rooms should be appropriately ventilated, but an AIIR is not routinely needed.
• Source control masking should be used by the patient when they leave their room (e.g., for transport to a procedure).
Special Air Precautions: “[These] are applied to patients with a respiratory pathogen, typically new or emerging, that is not observed or anticipated to spread efficiently over long distances (such as through ventilation systems), for which infection generally leads to more than mild illness, and where immunity (or vaccine) and effective treatment are not available,” the guidelines note.
• HCP should use a NIOSH-approved fit-tested N95 (or higher-level) respirator and eye protection on room entry.
• Place the patient in a private room. If not available, then cohort.
• Rooms should be appropriately ventilated, but an AIIR is not routinely needed.
• Source control masking is indicated for the patient when they leave their room (e.g., for transport to a procedure).
Extended Air Precautions: “[These] are used when providing care to patients with pathogens that are observed to spread efficiently across long distances and over extended times, such that room air needs to be contained (e.g., prevented from moving into the hallway where individuals are not appropriately protected),” the draft guidelines state.
• A NIOSH-approved fit-tested N95 (or higher-level) respirator is worn by HCP on room entry, and eye protection is used based on Standard Precautions.
• A private room is indicated.
• An AIIR is required.
• Source control masking is indicated for the patient when they leave their room.
• Travel outside the room should be limited (e.g., for necessary procedures and treatments).
In Sync with OSHA
In explanatory text in the guidelines, HICPAC clarifies that healthcare workers may go beyond the recommendations and wear an N95 respirator for routine air isolation.
“While not required for Routine Air Precautions, HCP may choose voluntarily to wear a NIOSH-approved N95 (or higher-level) respirator, per existing federal regulations,” the draft states.
This is apparently in accordance with Occupational Safety and Health Administration (OSHA) requirements for a respiratory protection program, but several HICPAC members said it was confusing to put it in a CDC guideline.
“I think when people are using N95s in a voluntary way when only isolation masks are recommended, it’s not for source control as much as for their own protection,” said Erica Shenoy, MD, PhD, medical director of infection control at Mass General Brigham. “They’re feeling that an isolation mask is not perhaps sufficient for their protection.”
OSHA requirements or no, allowing personal protective equipment (PPE) beyond the recommended level of protection could be problematic for a CDC guideline, sending a mixed message about what level actually is safe, she added.
In any case, many hospitals are not likely to allow a healthcare worker to voluntarily wear an N95 respirator if a surgical mask is indicated by the CDC, said Megan Hayden, RN, MS, CNS, CIC, CPH, an ex-officio member of HICPAC representing the Centers for Medicare and Medicaid Services (CMS).
However, the statement allowing a voluntary upgrade per OSHA regs remained in the approved draft guidelines. Similarly, although an AIIR is not recommended for Special Air Precautions, IPs may consider using such rooms for pathogens with uncertain transmission characteristics. Aerosol-generating transmission remains something of a gray area, but IPs can err on the side of caution if they suspect a procedure may create aerosols containing pathogen particles.
“There is neither expert consensus, nor sufficient supporting data, to create a definitive and comprehensive list of these procedures,” the HICPAC draft states. “Certain procedures that involve manipulation of the patient’s airway and close proximity between the patient and the HCP may increase [the] risk of pathogen transmission by air. Facilities may perform an infection control risk assessment to implement Special Air or Extended Air precautions for patients with certain target pathogens, or for all patients regardless of symptoms or confirmed infection, during certain higher risk procedures.”
A call for tight-fitting masks prompted several committee members to point out that this is not always the case, and altering the mask to tighten it typically is not recommended either.
Bell acknowledged such issues but said the CDC worded the guidelines in anticipation of a new mask that may soon be approved for medical use. “We were trying to make a place for these in this guidance as this comes forward,” he said. “You can purchase them now, but they’re not approved for medical use yet. There is still the FDA [Food and Drug Administration] hurdle to get medical device approval, but they are made of better filtration material, they fit better in general, and are less burdensome than formal respiratory protection. There might be an opportunity down the road to replace surgical masks with something that’s better.”
At the aforementioned listening session, former OSHA Director David Michaels, PhD, MPH, said, “Frankly, [the] CDC should be embarrassed and would be looked upon with great question if they conclude that surgical masks are equally as effective as respirators. The agency should consider this extremely seriously.”
It should be noted that the CDC only lowered its recommendation for N95s to masks after it became clear there was a national shortage of the respirators, caused in part by unchecked depletion of the national stockpile over a period of years before the pandemic.
Risk Assessment
While most of the committee review was wordsmithing, there were struggles at times to meet the goal of keeping the document compact while wanting to include more information. This came up in the discussion on the recommended infection control risk assessment under standard precautions. “I’m wondering if there’s any additional heft or context or detail that you would recommend to try and press the importance of risk assessment,” Bell said. There was a discussion of tools to do this, but the committee ultimately decided to stick to the principle of brevity.
“I think if we try to put too much into the guideline, people might start to think it’s meant to be all-inclusive,” said Elaine Dekker, RN, HICPAC member and infection prevention manager at San Francisco General Hospital. “We are trying to get people to think it through, and that’s a balancing act. We want to make sure that we emphasize preparing an IP to teach what to do at their facility based on their [policies] and their staff.”
The draft guidelines state that a risk assessment is “central” to adoption of standard precautions.
“Performing a risk assessment can be challenging, and HCP might not anticipate all potential opportunities for exposure,” the draft guidelines state. “To reduce this risk, facilities might choose to systematically apply elements of Standard Precautions to situations recognized as likely to present a risk of pathogen transmission. For example, because it can be difficult to anticipate if a patient with a respiratory infection will cough or sneeze during an encounter, facilities may choose to implement universal use of eye protection by HCP (in addition to the already indicated mask or respirator) for the care of patients with respiratory virus infections.”
The basic components of Standard Precautions are familiar, with the following tenets outlined by the committee:
• Hand hygiene;
• Environmental cleaning and disinfection;
• Injection and medication safety;
• Risk assessment with the use of appropriate PPE (e.g., gloves, gowns, masks) based on activities being performed;
• Minimizing potential exposures (e.g., having patients and visitors wear a mask when respiratory symptoms are present);
• Reprocessing of reusable medical equipment between each patient or when soiled.
HICPAC strived to write the guidelines in more understandable, straightforward language, since the CDC was widely criticized during the pandemic for issuing abstruse and sometimes contradictory recommendations. “Not a criticism but just a reality — there’s been a tremendous amount of confusion created for patients and families, and the hesitancy to enter healthcare facilities,” Lin said. “I think any kind of messaging has to be [understandable to] both healthcare workers and [patients].”
There was much discussion of PPE, with the elephant in the room the fact that there were considerable shortages at the onset of the pandemic in 2020.
“Employers in healthcare settings are required to provide readily available PPE to HCP, ideally at or near likely points of use,” the guidelines state. “Sizing and models should be chosen to accommodate the needs of the local workforce. Extended use is not considered standard practice and should be avoided unless otherwise specified in recommendations (e.g., extended use of masks for source control).”
REFERENCES
- Centers for Disease Control and Prevention. 2024 Guideline to Prevent Transmission of Pathogens in Healthcare Settings. https://www.cdc.gov/hicpac/pdf/DRAFT-2024-Guideline-to-Prevent-Transmission-of-Pathogens-2023-10-23-508.pdf
- 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. Type and duration of precautions recommended for selected infections and conditions. Appendix A updates [September 2018]. https://www.cdc.gov/infectioncontrol/guidelines/isolation/appendix/type-duration-precautions.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.
- Centers for Disease Control and Prevention. Scientific brief: SARS-CoV-2 transmission. Updated May 7, 2021. https://stacks.cdc.gov/view/cdc/105949
- Centers for Disease Control and Prevention. 2007 Isolation Guideline Update Listening Session. Oct. 10, 2023: https://www.cdc.gov/hicpac/pdf/2023-October-HICPAC-ListeningSession-508.pdf
New draft patient isolation guidelines recently approved by advisors to the Centers for Disease Control and Prevention call for scrapping the “outdated dichotomy” of droplet/airborne precautions in favor of a “continuum” approach to stop transmission through the air.
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