IHEEM DIGITAL WEEK – INFECTION CONTROL
A detailed look at COVID-19 and reducing transmission
Speaking in an IHEEM Digital Week webinar on 6 October, Professor Cath Noakes FIMechE, FIHEEM, of the School of Civil Engineering at the University of Leeds, took an in-depth look at how the COVID-19 virus is transmitted, the virus’s key characteristics, and at some of the key measures via which both individuals – through their own actions – and healthcare engineers working in healthcare facilities, can mitigate its spread.
Professor Noakes was introduced by session chair, Richard Harris, a director at Rolevale Services, and a member of the IHEEM Ventilation Technical Platform. Professor of Environmental Engineering for Buildings within the School of Civil Engineering at the University of Leeds, and a Chartered Mechanical Engineer, Cath Noakes has a background in fluid dynamics, and significant expertise in ventilation and indoor air quality. Her research group conducts experimental and modelling-based studies with a strong focus on ventilation – including exploring the transport of airborne pathogens, and the effectiveness of engineering approaches to controlling infectious disease transmission. An investigator on multiple projects, having worked with researchers across numerous disciplines, she has written over 100 peer-reviewed papers, and co-authored design guidance for CIBSE and the Department of Health. Also Deputy Director of the Leeds Institute of Fluid Dynamics, since April this year she has been led a UK SAGE sub-group focusing on the science underpinning the transmission of COVID-19.
What we already know
Beginning her presentation, ‘Hands, Face, Space, Ventilate – Engineering the Environment to mitigate COVID-19’, Prof. Noakes said she would be discussing ‘some of what we already know about transmission’, with a particular focus on droplets and aerosols and their role, and some of the engineering aspects of
Aerosol:
suspension of fine solid or liquid droplets in gas
Droplet:
very small drop of liquid
100 μm 1 μm
Human hair ~60 μm
Comparative size of aerosols and droplets. 10 μm
Professor Cath Noakes.
controlling transmission. It was now known that the virus – about which almost nothing had been known just nine months before – survives both in air and on surfaces, ‘with considerable laboratory data backing this up’. Showing her first slide, she said that in aerosol form the virus had a half-life of around an hour. However, to date there was very little real-world information available on the virus’s survival, necessitating reliance on laboratory test data. She said: “We know most of the transmission occurs inside, when people are close to eachother, with the droplets in exhaled breath.” There was also evidence of airborne transmission, albeit ‘not routinely’, and concerns over aerosol-generating procedures in medical and dental settings. In community settings,
airborne transmission tended to occur mainly in poorly ventilated spaces. Professor Noakes said: “While contact surface transmission also matters, we believe it may be a little less important than originally thought, perhaps only accounting for some 20 per cent of transmission. Certainly, good handwashing can reduce risk for this and other respiratory illnesses by 16-20 per cent.” Among the ‘most challenging’ aspects of SARS-CoV-2 was that people are most infectious in the early stages, often before they show any or many symptoms. The Professor said: “Essentially we have some very hard-to-identify silent transmitters among the population; some of them may be ‘superspreaders’. We believe this is a highly dispersed disease, i.e. about 10 per cent of the people are responsible for about 80 per cent of the transmission.”
Modes of transmission
Prof. Noakes explained that the primary source of the pathogen was respiratory aerosols and droplets containing the virus when somebody exhales. She explained: “The other source is anybody infectious, since they are likely to be quite contaminated, and may touch surfaces or people.” To be exposed to the virus, individuals could inhale the smaller
November 2020 Health Estate Journal 35
©Leeds Institute for Fluid Dynamics
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