In July, 239 scientists signed an open letter “appealing to the medical community and relevant national and international bodies to recognise the potential for airborne spread of covid-19.”1 Although the World Health Organization conceded that “airborne transmission cannot be ruled out,” the response was reserved and arguably mistaken in continuing to suggest that airborne and droplet transmission are discrete categories and that airborne transmission occurs only during medical “aerosol generating procedures.”
WHO defines droplets as ≥5-10 μm diameter and aerosols as <5 μm. However, both can be generated as a continuum of particle sizes during numerous respiratory activities and their behaviours are not distinct. This has important practical implications for infection control, the prevention of outbreaks and superspreading events, and for the new social behaviours that are being implemented in an effort to control the pandemic.
Strong signals
Since the 2003 SARS outbreak, research in aerobiology, physics, and computational fluid dynamics has advanced our understanding of aerosol generation and the carriage and fate of respiratory particles. Airborne transmission of covid-19 is now the plausible cause of superspreading events in a call centre in Korea, a choir practice in Skagit County, US, and a restaurant in Guangzhou, China.The pandemic is at a critical juncture, and these strong signals should not be ignored by politicians and public health leaders.
Urgent research is needed to better understand airborne transmission and measure viral aerosol outputs during respiratory activity and medical procedures. In the meantime, international guidance must acknowledge the weight of evidence supporting airborne transmission of covid-19 and include recommendations to promote effective preventive measures. How should infection control practice be changed if we provisionally accept that aerosols have an important role in viral transmission?
Inhalational risk may be reduced by social distancing, limiting interaction indoors, avoiding air recirculation, improved natural and artificial ventilation, and innovative engineering solutions which collect and neutralise aerosols to provide clean air in personal and community spaces.The infection risk associated with deep breathing, talking, and singing indoors is underappreciated and urgently needs attention.
Aerosol generating procedure is a misleading term, and its use probably leads to overestimation of risk in stable patients while proved aerosol generating activities such as coughing and talking are neglected.
The risk associated with individual procedures should instead be classified by measuring aerosol emissions, comparing them with those from other respiratory activities, and placing them in clinical context. In the interim, healthcare workers require access to respirator masks for all high risk encounters, not just during selected clinical procedures.
Controlling this pandemic is difficult when the fundamental science determining the response is misunderstood. Accepting the importance of airborne transmission may prove a crucial breakthrough and should not be delayed further.
Reference & source information: https://www.bmj.com/
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