The role contaminated surfaces in COVID-19 transmission: a HIS audience-led webinar

The next instalment of the HIS audience-led webinar series is on the role of contaminated surfaces in COVID-19 transmission. I was delighted to be part of the panel for this one:

  • Dr Lena Ciric – Associate Professor in Environmental Engineering, University College London
  • Dr Stephanie Dancer – Consultant Microbiologist, NHS Lanarkshire and Professor of Microbiology, Edinburgh Napier University, Scotland
  • Dr Manjula Meda – Consultant Clinical Microbiologist and Infection Control Doctor, Frimley Park Hospital
  • Dr Jon Otter – Infection prevention and control Epidemiologist, Imperial College London
  • Chair: Dr Surabhi Taori, Consultant microbiologist and infection control doctor, Kings College Hospital NHS Foundation Trust

Here’s the recording:

And here’s my take on the Q&A:

How long does the virus survive in different surfaces in the environment? Are there any factors which affect survival? The short answer is between <1 day and >7 days, depending on the substrate (porous/non-porous; copper), suspending medium (how gooy it is), concentration, and probably viral strain variation (although there isn’t a great deal of that in SARS-CoV-2 yet). The lab data also shows us that SARS-CoV-2 is susceptible to common disinfectants, as you’d expect for an enveloped virus. How does this translate to clinical settings? There is emerging evidence that the ‘usual’ drivers of shedding and contamination in hospitals apply to SARS-CoV-2, like the amount shed and presence of body fluids (symptoms, no symptoms), the physical environment (surfaces, airflows), and cleaning/disinfection protocols. Quite a few studies in clinical settings evaluating SARS-CoV-2 contamination of surfaces have identified widespread contamination with viral RNA but no culturable virus. What does this mean? It’s tricky to interpret, but this seems to highlight the potential risk from surface contamination but, since no culturable virus has been detected on surfaces in clinical settings, suggests that it’s not time to press the panic button and make a wholesale revision to cleaning and disinfection guidance and protocols!

Is there any evidence that more frequent environmental cleaning reduces transmission of COVID-19? What would be the most optimal cleaning regimen in the community and in hospitals? An audience poll showed that 95% of the audience had increased the frequency of cleaning during the pandemic, whereas only 25% had changed cleaning/disinfection product. The evidence-base for enhanced cleaning or a product switch to tackle SARS-CoV-2 is emerging, to say the least! We don’t understand the infective dose, the dynamic between hand and surface contamination, and the relative important of respiratory vs. contact routes. However, emerging evidence from SARS-CoV-2 and more established evidence from other respiratory viruses (e.g. SARS-CoV-1 and influenza) allows us to build an argument that surface contamination is likely to be important at least some of the time, and that enhanced cleaning frequency makes sense. The panellist (Dr Dancer) recommended either detergent or chlorine-based disinfectants, and I would add to this the option of using a non-chlorine based disinfectant provided it has efficacy against enveloped viruses (in line with current PHE guidelines). The approach outside of hospital may be different – but enhanced cleaning frequency and disinfection may be justified sometimes (especially in bathrooms and kitchens).

Which (other) measures are most effective in preventing environment to person transmission? I was surprised to see that half of the audience thought that hands/surfaces and droplets/aerosols are equally important in the transmission of COVID-19, and a third thought that droplets/aerosols are the most important route. There is uncertainty about which transmission route is the most important. We have strong evidence from other respiratory viruses that both contact (including fomites) and droplet/aerosol routes are involved in transmission – and that the relative importance of each route varies by the circumstances. We can learn from laboratory studies, environmental sampling, epidemiological studies, and animal/mathematical models to understanding what are likely to be the most effective and impactful interventions to prevent the spread of COVID-19.

What, if any, is the role of environmental sampling in managing the risk of transmission? I was surprised to see from the audience poll that environmental sampling is performed in about 25% of participants’ hospitals (although it wasn’t clear whether this was sampling for SARS-CoV-2)! Whilst the panel didn’t advocate routine surface sampling for SARS-CoV-2, environmental sampling can help us to understand transmission routes and, during outbreaks, to identify whether there are deficiencies in cleaning or a point-source fomite. Related to this, the use of DNA markers can help us to model the spread of viruses in clinical settings.

There are increasing reports of outbreaks of COVID-19 associated with abattoirs and meat processing plants. Do you think that surface contamination is relevant here as cleaning will be minimal, or is transmission more likely to be airborne/aerosol mediated? Or is it impossible to say? Abattoirs and meat processing plants offer a number of important challenges and transmission risk including low temperature, high concentrations of organic matter, frequent use of high-pressure washing devices (which may generate aerosols), and a workforce that often live and work together in close quarters. This makes it almost impossible to disentangle transmission routes. Therefore, surface hygiene must be addresses carefully along with other potential transmission routes.

The latest recovery guidance recommends creating red and green zones for patient pathways. What are the advantages and pitfalls of such segregation? Effective isolation of infective individuals is one of the key tenets of infection prevention and control. If we can effectively physically segregate (or should I say physically distance) infective from susceptible individuals then this will reduce the need for enhanced precautions to address surface contamination during the management of COVID-19. And the best way to do this is through the creation of “COVID-protected” pathways, which shouldn’t require enhanced precautions to address surface contamination. Outside of COVID-protected pathways, a risk-based decisions will need to be made as to whether enhanced precautions to address surface contamination are required.

How much longer does the virus survive on gloves than on bear hands and could the overuse of gloves be contributing to transmission? The panel were unaware of specific evidence on the survival of SARS-CoV-2 on gloves vs. bare hands but suspected that it would survive for longer on gloves than on bare hands (which have microbiocidal properties). However, this extended survival time is largely immaterial, because the virus will survive for long enough on surfaces and bare hands to be involved in transmission. Therefore, the focus should be on the careful use of gloves (much less frequently and for much shorter periods than is often seen!) and hand hygiene at the moments that really matter in preventing transmission.

Is the infectious dose from fomites known for SARS-CoV-2? The infectious does for SARS-CoV-2 is not yet known in general. However, looking at other respiratory viruses like influenza, can be as low as <1 TCID50 but is usually considered to be around 103. So, it’s likely to depend on the circumstances and it will require further work to understand the infectious dose from fomites.

2 thoughts on “The role contaminated surfaces in COVID-19 transmission: a HIS audience-led webinar

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