The COVID-19 pandemic has forever changed the approach we take in healthcare settings to protect healthcare personnel, patients, and others from transmission of respiratory infections. Experimental and observational data show that an important pathway for transmission of severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is via inhalation of small particles in the air generated by infected individuals. There is widespread recognition that inhalation of infectious particles is a primary pathway of disease transmission occurring over short distances in addition to large droplets and sprays landing on the mucous membranes when infectious people cough or sneeze. The observation that infections have characteristic distances over which they can be transmitted reflects factors including greater concentrations of infectious respiratory particles closer to infected individuals and differences in pathogen-specific factors such as the inhaled dose required to cause infection and the amount of time that a specific pathogen is able to remain infective.
The need to update the CDC guideline on isolation precautions to reflect this more up-to-date scientific view of how respiratory infections are transmitted was one of the important motivations for CDC to ask the Healthcare Infection Control Practices Advisory Committee (HICPAC) to undertake an update. HICPAC is a federal advisory committee appointed to provide advice and guidance to the Department of Health and Human Services and CDC regarding the practice of infection control in clinical settings. CDC plans for updates to the guideline to be accomplished in stages over a period of several years. The first step is to complete a framework document that will be part one of the updated Guideline to Prevent Transmission of Pathogens in Healthcare Settings. The framework provides the scientific foundations that will be used when prevention recommendations are developed for specific pathogens and clinical situations that will be subsequently developed through HICPAC as part two of the guideline.
A draft set of framework recommendations was reviewed by HICPAC in November 2023 and approved by the HICPAC committee for sending to CDC for review. The draft recommendations document is posted on the CDC website at https://blogs.cdc.gov/safehealthcare/november-hicpac-public-meeting-recap/.
Based on the significant interest in the draft recommendations, CDC is taking a proactive step of communicating back to HICPAC some initial questions and comments on which we would like additional consideration before submitting the guideline into the Federal Register for public comment. In addition, CDC is working to expand the scope of technical backgrounds of participants on the HICPAC Isolation Guideline Workgroup and eventually among the committee members through established processes in accordance with the Federal Advisory Committee Act (FACA) regulations and guidance. The expanded workgroup and the HICPAC with the newly appointed members will review and discuss these additional considerations and guideline at the next HICPAC meeting, which is open to the public.
A comprehensive CDC review has identified many positive aspects of the draft recommendations. The draft categorizes transmission pathways into two broad categories, air and touch, each with various subcategories. Within the broad category of transmission via air, the past dichotomy between transmission via large droplets versus airborne transmission via small particles has been eliminated, recognizing that there is a continuum of particle sizes that can transmit infection via deposition on mucosal surfaces and inhalation. The importance of the hierarchy of controls in preventing transmission of infection is clearly described. Although the document does not address engineering controls such as ventilation controls in detail, their importance is acknowledged and a separate, subsequent guideline will address the issue. The importance of anticipating transmission through air and using respiratory protection when caring for those with new and emerging pathogens represents another lesson learned from the COVID-19 pandemic.
The CDC review has also generated questions and comments for HICPAC’s consideration. More detailed explanations are provided below.
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We will describe two of them in more detail here, both related to preventing transmission of infection through air.
- The first issue is the approach to determining how pathogens that are transmitted via air, but not typically transmitted over long distances (such as through ventilation systems), should be managed. The draft document provides two options for this type of pathogen, “routine air precautions” and “special air precautions.” The main difference between them is that “routine air precautions” are directed toward infections that are common and for most people not severe, for which the precautions specify that healthcare personnel should wear a mask (i.e., surgical mask, face mask [sometimes called a procedure mask] or enhanced barrier face covering) while “special air precautions” are indicated to prevent transmission of infections that have greater or unknown potential to cause severe illness, for which the precautions specify that healthcare personnel should wear a NIOSH Approved N95 (or higher-level) respirator. This aspect of the draft has attracted much public comment because many have interpreted current text as limiting “special air precautions” only to new and emerging pathogens that cause severe, life-threatening disease. There is concern that, based on that perception, SARS-CoV-2 would revert to routine air precautions because, at this time, it is no longer new and emerging. There is also concern that adverse outcomes associated with substantial morbidity, such as long COVID, would not be considered in determining whether to apply routine or special air precautions because they might not be considered as representing severe disease.
- CDC believes that it would be helpful for HICPAC to clarify that special air precautions will be applied based on an assessment of risk of transmission and associated adverse outcomes. Important considerations for risk of transmission include: (1) that the pathogen is suspected or known to be transmitted via inhalation but not observed or anticipated to spread efficiently over long distances, such as through ventilation systems. New and emerging pathogens in which the major mode of transmission has yet to be determined but do not exhibit the ability to transmit over long distances can be assumed to be transmitted via inhalation until shown otherwise; (2) transmissibility (i.e., ease of spread as determined by factors related to pathogen, infected individuals, at-risk exposed individuals, contact patterns, and environmental conditions); and (3) burden of morbidity and mortality associated with infection among healthcare personnel, patients, visitors and others. Morbidity and mortality are affected by factors such as level of protective immunity in the population from vaccination or previous infection, the availability of effective treatment, and prevalence of personal risk factors that increase the risk of infection.
Another issue relevant to preventing transmission through air is to make sure that a draft set of recommendations cannot be misread to suggest equivalency between facemasks and NIOSH Approved respirators, which is not scientifically correct nor the intent of the draft language. Although masks can provide some level of filtration, the level of filtration is not comparable to NIOSH Approved respirators. Respiratory protection remains an important part of personal protective equipment to keep healthcare personnel safe.
We thank HICPAC for taking on the challenging task of updating our nation’s infection control isolation guidelines. The COVID-19 pandemic will not be the last one we face. We must be better prepared for the next pandemic and use what we have learned to improve approaches to preventing transmission of any pathogen spread through air in healthcare settings. The multi-year effort to update the isolation precautions guideline is a critical part of achieving that goal.
CDC letter to HICPAC
Attribution Statement: N95 and NIOSH Approved are certification marks of the U.S. Department of Health and Human Services (HHS) registered in the United States and several international jurisdictions.
Aut/about/leadership/leaders/niosh.htmlhors:
Daniel Jernigan, MD, MPH and John Howard, MD, MPH, JD, LLM, MBA
