Many health care facilities follow infection control policies that are based on outdated models of how respiratory viruses spread and should be revised, according to a team of leading experts that includes Dr. Donald K. Milton in the University of Maryland School of Public Health. A narrative review of current best practices and suggestions for needed policy updates is published today in Annals of Internal Medicine.
Traditional medical teaching suggests that most respiratory viruses are spread through droplets. These are larger particles that are heavy enough that they will rapidly fall to the ground within one to two meters of an infected person. Public health agencies have traditionally advised health care workers to wear surgical masks to protect themselves from droplet organisms. The one exception has been for patients undergoing so-called “aerosol-generating procedures”(e.g., during intubation) in which case higher levels of respiratory protection, such as N95 respirators, are recommended.
Researchers from Harvard Medical School, Harvard Pilgrim Healthcare Institute, the University of Maryland School of Public Health (College Park) and the University of Maryland School of Medicine (Baltimore) reviewed published studies looking at SARS-CoV-2 transmission and infection control policies. They found that the traditional model of how respiratory viruses are spread may be incorrect. Most studies now suggest that respiratory viruses are primarily transmitted by aerosols. These are smaller respiratory particles that can remain suspended in the air for long periods of time, can travel beyond two meters from the source patient, and most importantly, can bypass surgical masks. People routinely generate aerosols whenever they exhale, particularly when speaking loudly, breathing heavily, or coughing. Most so-called “aerosol-generating procedures” by contrast do not meaningfully increase aerosol generation relative to talking and heavy breathing. The risk of inhaling infectious aerosols is greatest close to an infected person and in poorly ventilated spaces and prevention is made more difficult because people can be infectious without having symptoms.
These insights suggest that researchers and public health specialists should reexamine recommended transmission prevention methods. The authors urge a uniform set of respiratory precautions for all respiratory pathogens and high-risk interactions rather than differentiating between different kinds of viruses and procedures and focusing on preventing transmission among people regardless of symptoms and known infection status. The publication offers guidance on the creation of graded, risk-based approaches to prevent transmission in health care facilities that take into consideration the amount of disease in the community, patient factors, and care factors that better predict transmission risk.
The paper Current Insights Into Respiratory Virus Transmission and Potential Implications for Infection Control Programs: A Narrative Review was written by Michael Klompas, MD, MPH, Donald K. Milton, MD, DrPH, Chanu Rhee, MD, MPH, Meghan A. Baker, MD, ScD and Surbhi Leekha, MBBS, MPH and published in the Annals of Internal Medicine.
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