Asymptomatic and pre-symptomatic transmission in UK care homes – and infection, prevention and control (IPC) guidance – an update

Dr Sarah House and Eric Fewster

This Post is an update from the one posted here: Mapping of UK Government Guidance for Infection Prevention and Control (IPC) for COVID-19 in Care Homes.

A range of studies have been available from January 2020 onwards, from a cruise ship, from individual households and from care homes and residential contexts, that had identified the issue of pre- and asymptomatic presence and viability of the virus and its transmission – for example from: USA, Singapore, Germany, China etc.

A document listing some of the references (although there are many more) is available here:

Studies in the USA indicated in a skilled nursing facility that 57% of all positive cases in residential settings were asymptomatic or pre-symptomatic and in one homeless facility 87% of positive cases were asymptomatic. A range of other cases studies from China and Singapore, have identified specific cases where the transmission has been from an asymptomatic or pre-symptomatic person; and analysis of larger data sets has estimated that between 6.4 – 12% of positive cases had come from asymptomatic or pre-symptomatic transmission. The ONS in the UK is even stated in the media on 5 June 2020 that 70% of the COVID positive cases in the community in the UK have been found to be asymptomatic.

Increasing numbers of bodies responsible for strategic guidance to respond to the COVID-19 outbreak, are recognising the importance of the risk of asymptomatic and pre-symptomatic transmission. Yet it seems that very little if any emphasis has been put on asymptomatic or pre-symptomatic transmission in UK government strategies and IPC guidance for the pandemic response and in particular for care homes, even to date.

What is advised on this issue in other countries and globally?

USA Centres for Disease Control (CDC):

The CDC states on its webpage (23 May 2020): Key Strategies to Prepare for COVID-19 in Long-Term Care Facilities (LTCFs)

  • “If COVID-19 is identified in the facility, restrict all residents to their rooms and have HCP wear all recommended PPE for care of all residents (regardless of symptoms) on the affected unit (or facility-wide depending on the situation). This includes: an N95 or higher-level respirator (or facemask if a respirator is not available), eye protection, gloves, and gown. HCP should be trained on PPE use including putting it on and taking it off”. “This approach is recommended because of the high risk of unrecognized infection among residents. Recent experience suggests that a substantial proportion of residents could have COVID-19 without reporting symptoms or before symptoms develop”.

Hong Kong:

Professor Terry Lum, Head of Social Work and Social Administration, Hong Kong University during the Parliamentary expert consultation by the Health and Social Care Committee on 19 May ( talked about how the authorities in Hong Kong used what they learnt from SARS to have huge successes in their response – with the result that they have had zero deaths of health staff and zero infections and deaths in care homes. He stated that it is important to understand that the virus load peaks 2 days before the onset of symptoms and from January 2020, all workers in care homes had to wear face masks.  

World Health Organisation:

The World Health Organisation in its latest guidance on the use of face masks has referred to a wide range of evidence on the high proportion of positive cases that are asymptomatic or pre-symptomatic and acknowledged that transmission is happening from these groups – see the reference list in this document:

It has also acknowledged the same issue in its updated guidance for care homes in Europe:

How has asymptomatic and pre-symptomatic transmission been considered in the UK and its IPC guidance for care homes?

SAGE – 28 January 2020:

UK scientists, Public Health England and the UK Government have been aware of the issue of asymptomatic and pre-symptomatic transmission since January 2020. The UK SAGE group (the scientific advisory group who advise the UK government) raised the issue of asymptomatic transmission back in January 2020. In the parts of the SAGE meeting notes #2 – 28 January 2020 – that were released: ( – it notes:

  • “There is limited evidence of asymptomatic transmission, but early indications imply some is occurring. PHE developing a paper on this”.
  • “ACTION: PHE to share paper on asymptomatic transmission with SAGE”.

We have not yet been able to establish if this report was prepared or released to the public.

SAGE – May 2020:

Scientists advising the UK Government have continued to flag this issue with the government as being a gap in the current guidance. In an interview on BBC on the 18th May, Professor Susan Michie, Professor of Health Psychology, Director of the Centre for Behaviour Change at UCL, who is on the SAGE Behavioural Science group, said that “no-one is talking about the fact that a person is most infectious 2-days before the symptoms start” and that “this is an important issue to communicate”.

UK Government Science and Technology Committee – May 2020:

On the 18th May, the UK Government Science and Technology Committee wrote to the Prime Minister identifying the lack of attention on asymptomatic transmission as being a major gap in the UK Government’s strategies and have recommended that the government needs to explicitly set out its strategies to managing asymptomatic transmission: They stated that (pp.13-14):

  • Finding 6: Strategies to deal with carriers of COVID-19 who were asymptomatic have not been clear.
  • Recommendation 6: The Government should explicitly set out its approach to managing the risk of asymptomatic transmission of the disease.

Public Health England and HM Government / CARE documents:

A few mentions have been made in occasional documents by Public Health England and HM Government / CARE, that asymptomatic and pre-symptomatic transmission is important including in care homes. Usually this has focussed on one specific aspect of the response, such as related to transmission by staff, but it does not mention it for other aspects, such as for person to person transmission within the home. For example:

NHS Scotland and Public Health Scotland – May 2020:

NHS Scotland and Public Health Scotland have also gone a step further and started to come up with their own practical guidance in response to this issue in relation to testing of staff and residents:

  • On the 16 May the Scottish Government made their own decision on this after NERVTAG declined to give clear recommendations at the end of April – NHS Scotland and PH Scotland published this interim guidance on testing which acknowledges the risks from pre- and asymptomatic transmission in care homes: This was published after NERVTAG “declined to provide definitive recommendations on how asymptomatic test positive cases should be managed” (p.7). They have said that: “This guidance has therefore been developed using a consensus-based model and is being published as ‘interim’ guidance, to be updated in light of new evidence and lessons learned by care professionals and local HPTs from practical experience”.

What is very positive about this step and approach, is that the Scottish Government seems to have listened to the evidence that has been coming from the ground, from the people working face-to-face with this pandemic in the Scottish care homes and the HPT supporting the people working in the Scottish care homes and has triangulated this evidence with the documented academic evidence. Both are important forms of evidence. They have used the precautionary principle and have gone ahead and worked with the local HPTs and care professionals to come up with practical recommendations based on the consensus model and common sense, to start to respond to this issue now rather than later. 

UK main IPC guidance – 21 May:

But the main UK Government IPC guidance document (“COVID-19: infection prevention and control (IPC) guidance”, updated 21 May, is still not clear enough on the importance of asymptomatic or pre-symptomatic and provides contradictory statements. For example (p.11):

  • Incorrect still on 21 May: “Infection control advice is based on the reasonable assumption that the transmission characteristics of COVID-19 are similar to those of the 2003 SARS-CoV outbreak”.
    • Incorrect still on 21 May: “Assessment of the clinical and epidemiological characteristics of COVID-19 cases suggests that, similar to SARS, most patients will not be infectious until the onset of symptoms. In most cases, individuals are usually considered infectious while they have symptoms; how infectious individuals are, depends on the severity of their symptoms and stage of their illness”.

What needs to be done for the UK’s main IPC guidance including that given to care homes?

The consideration of asymptomatic and pre-symptomatic transmission, as well as pauci-symptomatic transmission (mild symptoms) and a-typical symptoms (other than the three main ones identified in the UK, but which can be more common for older people, such as delirium) are still not yet core to the IPC guidance for care homes in the UK. This leaves a significant gap for the people working in care homes to know what the key risks of transmission are, and what to practically do to prevent the spread within care homes and to keep their staff and residents safe.

And as we noted in our previous post in mid-April, the useful parts of the UK guidance on IPC for care homes also still remains scattered and not clear.

More therefore has to be done urgently to update UK IPC guidance for care homes. We have already suggested various actions that should form part of an IPC strategy (see which could be used as a basis.

We recommend that the UK agencies with responsibilities for care homes (i.e. the UK Government / Department of Health and Social Care; NHS, Public Health England/Scotland/Wales, Public Health Agency, the Clinical Commissioning Groups, Care Quality Commission) do the following:

  • Provide strategic and practical guidance for care homes on infection prevention & control that:
    • Is all in one-place and supported by all agencies together, so as to prevent more confusion. All previous guidance that is used across contexts and scattered online (and is still publicly available) therefore needs to be changed / updated / superseded.
    • Uses the precautionary principle and is much clearer about what measures are needed to respond to the risk of asymptomatic and pre-symptomatic transmission, which is needed if we are to properly manage environments to prevent transmission of this virus (especially in closed environments where there are groupings of people, especially vulnerable people). Staff movement is one aspect, but it is not the only one, and there are many others including transmission resident-to-resident and resident-to-staff.
    • Rigorously covers all aspects of IPC and for all tasks in the care homes. So this mean not just focusing on PPE or staff or testing, but also on how to zone in order to establish transmission risks across the home so that risk-mitigating plans can be made for all of the practical tasks within the home, such as laundry, meals, personal hygiene, and as the outbreak reduces, communal activities, visits etc.
    • Is practical with step-by-step actions for each task.

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