Asymptomatic transmission of covid-19
BMJ 2020; 371 doi: https://doi.org/10.1136/bmj.m4851 (Published 21 December 2020) Cite this as: BMJ 2020;371:m4851Read our latest coverage of the coronavirus outbreak
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Dear Editor
This matters so much now because our ability as GPs in maintaining trust [1] with patients in our ‘Deep End’ [2] areas, is in jeopardy. Already in north east London, worst affected by Covid-19, we have a legacy of patients consulting more [3], feeling less enabled after consultations and doctors more stressed [4]. Race(ism) and place determine the health outcomes in our communities. The opportunity to support us, as clinicians, with informed evidence so that we can, with trust, coproduce decisions with patients is being missed by the delay in accepting the wider definition of symptom inclusion.
And again, the overlooked evidence of the accumulation of multi-morbidity in areas of deprivation [5] compounded by race(ism) where the biological age of 65-year olds the equivalent of 80-year olds in areas of affluence. The current JCVI categories for vaccination, without the flexibility of tailoring for local conditions further erodes our ability to maintain trust, with a knock-on effect in a reticence to embrace vaccination.
Compassionate informed clinical leadership is urgently needed to help us in numerous ways to restore the trust that our patients and communities need, to be enabled to do the best for their health.
[1] Watt G, Brown G, Budd J, et al. General Practitioners at the Deep End: The experience and views of general practitioners working in the most severely deprived areas of Scotland. Occas Pap R Coll Gen Pract. 2012;(89):i-40.
[2] GMC Maintaining Trust https://www.gmc-uk.org/ethical-guidance/ethical-guidance-for-doctors/goo...
[3] GP funding formula masks major inequalities for practices in deprived areas BMJ 2014;349:g7648
[4] The Inverse Care Law: Clinical Primary Care Encounters in Deprived and Affluent Areas of Scotland DOI: https://doi.org/10.1370/afm.778
[5] Epidemiology of multimorbidity and implications for health care, research, and medical education: a cross-sectional study https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60240-2/fulltext
Competing interests: No competing interests
Dear Editor,
I am writing to echo Alex Sohal's response that the UK should adopt the broader WHO criteria for covid. It is imperative that everyone in the population has appropriate access to testing, but more importantly that everyone self-isolates and changes their behaviour appropriately, and all are informed of the limitations of testing. Case rates in Newham have been consistently high so any resident can test even without symptoms, however, I have spoken to so many patients who have typical viral symptoms (not necessarily the publicised triad) and are surprised when I say I think their result is a false negative. My understanding of the sensitivity of covid swabs is that 3/10 negative results are false negatives - I may not be entirely up to speed with the latest data but the general public definitely need to know the limitations of testing. We urgently need a public health campaign that includes all recognised symptoms and focuses on clinical definition rather than test results.
I became unwell just before the March lockdown and was able to input my symptoms into the brand new Zoe Covid symptom app from about Day 4. My temperature remained below 37.8 so I never reached the case definition at the time but all my abdominal and skin symptoms were listed in the app. 16 weeks later my antibody test was negative. I had similar symptoms again very mildly in November and self-isolated despite a negative throat swab. Have I had covid once or even twice? Very probably. So many of us under 50 get such mild symptoms that it's tempting to dismiss the possibility of covid; it's unsurprising that those with less information and financial security than I have make a call that they don't need to self-isolate - and the government is colluding with this.
Too many people have paid with their lives for this laissez faire strategy. In the past 5 weeks in east London this includes a GP, a dentist, and a headteacher (in his 40s), all of whom had a much higher risk of covid exposure through their work. Unless we change to a broader case definition, with adequate support for households to self-isolate and wider access to testing we will face further overwhelming spikes of infection and lose more of the individuals we so badly need to rebuild our public services.
Competing interests: No competing interests
Dear Editor
My experience as a general practitioner is of regularly reviewing patients with mild symptoms—for example, a runny/blocked nose, sore throat, hoarseness, myalgia, fatigue, and headache—who subsequently turn out to be covid positive. These symptoms are often inadvertently picked up while dealing with patients’ other more pressing health issues. These patients have frequently not even considered that they may have covid-19 and have not self-isolated in the crucial early days when they were most infectious. The national publicity campaign highlights cough, high temperature, and loss of smell/taste as symptoms to be aware of; with only these allowing patients to access a covid-19 test online via the NHS test booking site. General practitioners have to advise patients to be dishonest to get a covid test. In my view, this is unacceptable.
The World Health Organization’s case definition of covid includes coryza, sore throat, myalgia, fatigue, headache, loss of appetite/nausea/vomiting and diarrhoea.(1) NHS guidance states that patients should keep self-isolating for more than ten days if they have a runny nose or sneezing.(2) The Royal College of Paediatrics and Child Health guidance for schools states that a cold does not require covid testing.(3) Yet children with laboratory confirmed SARS-CoV-2 have presented with nausea/vomiting, sore throat, and runny noses.(4)
I see no justification for not including coryza/cold or the WHO symptoms of covid in the UK covid case definition immediately. To date, in the UK, people with mild symptoms have not self-isolated, and instead have continued to go to work and attend school. During the current lockdown, there are an estimated eight million people in the UK who cannot work from home, many in public facing jobs, and with their children still attending school, as part of key worker provision. Their employers, managers, and teachers are mostly unaware of the significance of mild symptoms that could be covid-19.
National public health guidance needs to be clearer on what the symptoms of covid can be and tell the public that even those with mild symptoms (not only a cough, high temperature, and a loss of smell/taste) should not go out, self-isolating most importantly for the first five days, the time that they are most likely to be infectious,(5) or until they have a negative covid test. The media focus mostly on severe cases means that the public imagine covid as only a killer virus that makes it difficult to convince patients that their mild illness could be covid.
Data from the COVID Symptom Study shows a relatively low number of truly asymptomatic cases.(6) Studies that have reported high numbers of asymptomatic cases focus on persistent cough, high temperature, and loss of smell, missing many other symptoms. There is a data gap as much of our existing data on covid-19 comes from hospital settings,(7) not the cases I see in the community. One third of the population with covid-19 who are said to be asymptomatic may well have other symptoms, just not a cough or high temperature – this is not the same as being asymptomatic. Furthermore, Professor Pollock’s Editorial highlights that there is no robust evidence that the asymptomatic drive COVID transmission.(8) Thomas Drosten, Germany’s leading virologist, has written that as the new variant (B.1.1.7) is missing a gene that worsens the severity of the disease, therefore it could be more harmless, spreading faster, by causing milder disease, resulting in people with mild symptoms not self-isolating, instead increasingly infecting others.(9) This may partially account for the new variant being 70% more transmissible.(10, 11)
By changing the covid case definition, and informing the public, we could allow testing for more symptoms, identify more infectious cases, and reduce spread. The UK is currently in a third national lockdown, with schools closed. We need to consider the best strategy for easing and coming out of this present indefinite lockdown and making sure that we do not return to lockdown again, as covid-19 may well globally become endemic. Reconsidering the guidance on when patients should not go out and instead test for covid-19 may be a crucial step towards this. As important, as making sure that all workers and families have the support and means necessary to self-isolate, when they have symptoms or a positive covid-19 test.
Alex Sohal is a GP at Chrisp Street Health Centre, Health Equity Tower Hamlets Lead and Honorary Clinical Senior Lecturer in primary care, QMUL.
Competing interests: None
1. https://www.who.int/publications/i/item/WHO-2019-nCoV Surveillance_Case_Definition-2020.2
2. https://www.nhs.uk/conditions/coronavirus-covid-19/self-isolation-and-tr...
3. https://www.rcpch.ac.uk/sites/default/files/generated-pdf/document/COVID...
4. Swann Olivia V, Holden Karl A, Turtle Lance, Pollock Louisa, Fairfield Cameron J, Drake Thomas M et al. Clinical characteristics of children and young people admitted to hospital with covid-19 in United Kingdom: prospective multicentre observational cohort study BMJ 2020; 370 :m3249
5. Cevik M, Tate M, Lloyd O, Maraolo AE, Schafers J, Ho A. MERS-CoV Viral load dynamics, duration of viral shedding, and infectiousness: a systemtic review and meta-analysis. The Lancet Microbe. Volume 2, Issue 1, Jan 2021. DOI: https://doi.org/10.1016/S2666-5247(20)30172-5
6. https://covid.joinzoe.com/data
7. Wells PM, Doores KJ, Couvreur S, Malim MH, Spector T, Steves C. Estimates of the rate of infection and asymptomatic COVID-19 disease in a population sample from SE England. Journal of Infection. 2020 Oct. DOI: https://doi.org/10.1016/j.jinf.2020.10.011
8. Pollock A & Lancaster J. Asymptomatic transmission of covid-19. BMJ 2020;371:m4851
9. Kron T. Coronavirus variant: concern and observation yes, fear-mongering, of course not. Univadis Medical News. 2020 Dechttps://www.bmj.com/content/371/bmj.m4851
10. Volz E at al. Report 42 - Transmission of SARS-CoV-2 Lineage B.1.1.7 in England: insights from linking epidemiological and genetic data
11. https://www.youtube.com/watch?v=G3CT9N89L-c&feature=youtu.be
Competing interests: No competing interests
Dear Editor
Very recently the Chinese Centre for Disease Control and Prevention released that an antibody prevalence rate surveyed in Wuhan one month after the first wave of covid-19 pandemic was contained was 4.43%, [1] meaning that far more people might have been infected with SARS-CoV-2 than Wuhan’s officially counted cases (about 50,000) and may also be suggestive of asymptomatic transmission that cannot be easily overlooked. Actually, in the early days of the first emergence of covid-19, medics were struggling to trace its asymptomatic transmission and got some clues. [2]
Pollock and Lancaster believe that the symptomatic are more contagious than the asymptomatic, and thus symptomatic transmission has a greater role in the spread of SARS-CoV-2 requiring more attention and (limited) resources to handle symptomatic people (especially in an epidemic area), [3] which is also in compliance with common knowledge. Nevertheless, asymptomatic transmission may play a leading or bigger role in seeding SARS-CoV-2 or for the virus to gain a foothold in an immunologically naive community in a new covid-19 outbreak (below the radar).
For example, a covid-19 outbreak in September/October 2020 in Qingdao (China) in which there was no local transmission of SARS-CoV-2 for two months was probably triggered by two asymptomatic cases who were dock workers from the city’s port and had contracted the virus from ship workers or contaminated cargo. [4] Due to a new covid-19 outbreak in Beijing in late December 2020, the authorities have already locked down parts of Shunyi (a district in the northeast of the Chinese capital), and the source of this outbreak was finally tracked down to an imported Indonesian asymptomatic SARS-CoV-2 carrier. [5]
The finding from post-lockdown SARS-CoV-2 nucleic acid screening in Wuhan found no evidence of asymptomatic transmission.[6] However, first, notably the screening program was done several weeks after the city underwent two and a half months’ lockdown; then there were no new symptomatic cases found, and a small number of asymptomatic cases identified (via a positive PCR result) might already reach post-infection just with remaining viral RNA fragments and without transmissible viable virus (not truly asymptomatic cases). Second, sustained public health measures in Wuhan such as wearing masks and keeping social distancing might well effectively block covid-19 spread from (irregular and/or short-lived) viral shedding from asymptomatic cases, “silently” removing them from circulation. Perhaps it is truly challenging to find out ironclad proof for demonstrating or excluding asymptomatic transmission of covid-19.
References
1 Chinese Centre for Disease Control and Prevention. Seroprevalence of antibodies to SARS-CoV-2 across China (in Chinese). Dec 28, 2020. http://www.chinacdc.cn/yw_9324/202012/t20201228_223494.html (accessed Jan 2, 2021).
2 Bai Y, Yao L, Wei T, Tian F, Jin DY, Chen L, Wang M. Presumed Asymptomatic Carrier Transmission of COVID-19. JAMA 2020;323(14):1406-1407. doi: 10.1001/jama.2020.2565.
3 Pollock AM, Lancaster J. Asymptomatic transmission of covid-19. BMJ 2020;371:m4851. Doi: 10.1136/bmj.m4851.
4 Xing Y, Wong GWK, Ni W, Hu X, Xing Q. Rapid Response to an Outbreak in Qingdao, China. N Engl J Med 2020;383(23):e129. doi: 10.1056/NEJMc2032361.
5 The source of Cluster of COVID-19 cases in Shunyi district of Beijing was found (in Chinese). Dec 31, 2020. https://new.qq.com/rain/a/20201231a0087a00 (accessed Jan 2, 2021).
6 Cao S, Gan Y, Wang C, et al. Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China. Nat Commun 2020;11:5917. doi: 10.1038/s41467-020-19802-w .
Competing interests: No competing interests
Dear Editor
Is "the absence of strong evidence that asymptomatic people are a driver of transmission" of the SARS-CoV-2 virus not also a good reason for the state's relinquishing its restrictions on liberties, sociability and the economy which are seemingly predicated on such transmission, and yet so very damaging?
I think we are well due a proper conversation about how we relate to nature and its vicissitudes.
Jonathan Burton
Competing interests: No competing interests
Dear Editor,
Professor Pollock’s leader with James Lancaster is most timely, just as politicians are proposing a staggered start to the January school term whilst rolling out mass testing of teachers and pupils. This has all been predicated on an assumption that asymptomatic children testing positive are pushing community transmission rather than simply reflecting it, something for which there is no evidence.
Those who argue it is worth doing absolutely anything which might help have largely ignored the problem of false positives. Even at 1% FPR, 1000 children tested weekly in a large secondary school will produce 10 false positives -- ie more than one in every year group -- potentially closing the school. Prompt testing of symptomatic people followed by targeted serial testing of contacts would be a much better use of the new rapid tests.
Competing interests: No competing interests
Dear Editor,
As we have now adequate testing capacity for Covid-19, it may appear sensible to use the excess to look for asymptomatic cases. Prof. Allyson Pollock rightly points out the evidence that asymptomatic patients are probably not a major source of transmission(1). A better use of capacity may be to repeat test those with symptoms but who initially test negative.
The operational false-negative rate in the uk remains unknown. A systematic review reported false negative rates between 2% and 29%, with unexplained heterogeneity, that the authors felt "reinforce the need for repeat testing in patients with suspicion of SARS-CoV-2". (2)
This has never been done in the community setting in the UK, and while initial testing was performed by trained clinicians it is now standard practice for patients to take their own swabs, even in testing centers. This added uncertainty of self testing is recognised in the ONS modelling of the COVID-19 Infection Survey, where they present 2 scenarios. Scenario 1 uses a sensitivity of 90%, but scenario 2 uses a sensitivity of 60%, " to allow for the fact that individuals are self swabbing" (3). This is a wide confidence interval for such an important test.
A study of the accuracy of self collected samples in patients known to have SARS-CoV-2 has now been published indicating that self-testing has a sensitivity rate 75% (against 82.8% when taken by a health care worker); a false negative rate of 25% (4).
At the time of writing 1 false positive for every 3 positive cases would mean that over 10,000 patients are being misdiagnosed, and told they are negative when they are positive, every day. Guidance is that patients who test negative and feel well do not need to self isolate, nor do their contacts (5). The implications as to how this may increase the spread of Covid-19 is obvious.
A second test a day or so later would significantly reduce the number of false positives.
(1)https://www.bmj.com/content/371/bmj.m4851
(2) https://www.medrxiv.org/content/10.1101/2020.04.16.20066787v2
(3)https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/...
(4) plosone/article?id=10.1371/journal.pone.0244417
Competing interests: No competing interests
Dear Editor
Thank you for writing this piece. I have spent hundreds of hours researching this topic and have been totally frustrated in the lack of real data collected on this yet the lockdowns in many countries are based on these assumptions. If this virus is like all others and just maybe we have a little transmission before symptoms then the economy crushing lockdowns are not necessary. Japan has shown antibody tests currently at 46% prevalence up from 6% in May. This maybe due to allowing mildly infected people roam free and mildly infect others. That''s how it has worked the past thousand years. One can find plenty of articles titled proof of asymptomatic transmission in the media with none showing any proof. Sad.
Competing interests: No competing interests
Re: Asymptomatic transmission of covid-19
Dear Editor,
As the article says, about half of those who are initially asymptomatic go on to develop symptoms and hence are more contagious. A recent meta-analysis (below) indicates that an asymptomatic Covid patient transmits at about one-quarter of the rate of a symptomatic one, not a rate of zero. While I can see the argument that mass testing to find asymptomatic patients may not be a wholely justifiable approach, this article does NOT support the idea that restrictions, hand hygiene, mask wearing and social distancing should be stopped, as some have suggested.
https://www.nature.com/articles/d41586-020-03141-3
Competing interests: No competing interests