Questions remain about airborne transmission of COVID-19
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Although there is not yet solid evidence of airborne transmission of SARS-CoV-2, the coronavirus that causes COVID-19, a “reasonable assumption” can be made that it may occur, said Anthony S. Fauci, MD.
Fauci, the director of the National Institute of Allergy and Infectious Diseases, made his remarks during a press conference for the virtual AIDS 2020 meeting, after the publication of a commentary in Clinical Infectious Diseases urged the medical community “to recognize the potential for airborne spread of COVID-19.” The commentary, which was supported by 239 scientists, explained that several retrospective studies performed after the SARS epidemic in the early 2000s showed airborne transmission was the “most likely mechanism” to explain the spatial pattern of infections. According to the authors, a retrospective analysis demonstrated the same to be true for SARS-CoV-2.
The authors noted that studies conducted on the spread of other viruses, including RSV, MERS and influenza, also demonstrated that viable airborne viruses can be exhaled and/or detected in indoor environments where infected patients are present. This creates a risk for infection among people sharing these environments and, according to the authors, “there is every reason to expect that SARS-CoV-2 behaves similarly and that transmission via airborne microdroplets is an important pathway.”
The authors acknowledged that there is not yet widespread acceptance regarding airborne transmission of SARS-CoV-2 but argued that enough supporting evidence exists to warrant caution. They also expressed concern that the current measures put in place to control the virus, including hand washing and social distancing, are not enough to combat potential airborne transmission.
WHO ‘evaluating’ airborne transmission
WHO addressed the commentary in a press briefing and in a scientific brief published on July 9.
During the press briefing, Benedetta Allegranzi, MD, DTM&H, coordinator of WHO’s infection prevention and control global unit, and Maria D. Van Kerkhove, PhD, head of WHO’s emerging diseases unit, acknowledged that — because new evidence regarding COVID-19 is constantly emerging — it is necessary to be open to evidence regarding modes of transmission.
The scientific brief also acknowledged the “many unanswered questions” surrounding types of COVID-19 transmission and included a section on airborne transmission.
The brief stated that WHO, and the broader scientific community, are “actively discussing and evaluating” whether the virus can spread through aerosols outside of aerosol-generating procedures in the medical setting, especially in indoor settings with poor ventilation.
‘Something of a debate’
Airborne transmission of COVID-19 remains “something of a debate” among experts, according to Amesh A. Adalja, MD, senior scholar at Johns Hopkins Center for Health Security.
“Many of us in the infectious disease, infection control and epidemiology communities don’t really see the epidemiological spread that’s consistent with an airborne disease when you compare this coronavirus with, for example, measles, tuberculosis or chickenpox. Those are the classic airborne-transmitted organisms,” Adalja told Infectious Disease News. “COVID-19 does not have the same type of spread.”
Adalja acknowledged the role of aerosol-generating procedures, such as bronchoscopy or intubation, in COVID-19 transmission.
“The question for me is whether or not some aerosolization that occurs during normal activity is responsible for a lot of spread,” he said. “Should that change the way we approach protecting ourselves against this virus? That’s something that hasn’t been answered, I don’t think.”
John Lynch, MD, MPH, associate professor of allergy and infectious diseases at University of Washington School of Medicine and associate medical director of Harborview Medical Center, said the take-home message of the commentary in Clinical Infectious Diseases is that better ventilation is needed in closed settings.
“Recommendations around ventilation have always been part of infection control, but they may have been passed over and not focused on,” he told Infectious Disease News. “Those of us in infection control, or those of us who are focused on COVID-19 transmission, are really focused on personal protective equipment, but we do, in disease prevention, think about things like ventilation and air changes and filters very early on.”
Lynch said ventilation “is an often-overlooked component of buildings, especially outside of health care.
“As people reenter buildings — and we think about increasing the number of people in buildings, including schools — readdressing ventilation in those settings is going to be a very important part of it,” he said. “Even if it decreases a small percentage of transmissions, that is going to be worthwhile.”
- References:
- Morwaska L, Milton DK. Clin Infect Dis. 2020;doi:10.1093/cid/ciaa939.
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