Mass testing for covid-19 in the UK
BMJ 2020; 371 doi: https://doi.org/10.1136/bmj.m4436 (Published 16 November 2020) Cite this as: BMJ 2020;371:m4436Linked Opinion
Screening the healthy population for covid-19 is of unknown value, but is being introduced nationwide
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Dear Editor,
COVID-19 is a new disease, and obviously many things about it are not yet known for sure. But John Stone's questions (1) are really good because they force us to try to clarify concepts and put together the available pieces of a puzzle (which, however, will remain incomplete today).
While more information becomes available every day, many questions about transmission remain. Infected people can transmit the virus both when they have symptoms and when they don’t have symptoms. Current evidence suggests that COVID-19 spreads between people through direct, indirect (through contaminated objects or surfaces), or close contact with infected people via mouth and nose secretions. These include saliva, respiratory secretions or secretion droplets. These are released from the mouth or nose when an infected person coughs, sneezes, speaks or sings, for example. People who are in close contact (within 1 metre) with an infected person can catch COVID-19 when those infectious droplets get into their mouth, nose or eyes. There have been reported outbreaks of COVID-19 in some closed settings, such as restaurants, nightclubs, places of worship or places of work where people may be shouting, talking, or singing. In these outbreaks, aerosol transmission, particularly in these indoor locations where there are crowded and inadequately ventilated spaces where infected persons spend long periods of time with others, cannot be ruled out (2).
Moreover, it is said that “rapid antigen tests are effective, inexpensive and could end the pandemic in a few weeks (in theory)” (3). It is the frequency that really matters (4). What has been seen is that where there is frequent testing, outbreaks simply do not occur. The accuracy of a test depends entirely on what its objective is. If the target of rapid antigen tests is infectious people, which is really the most important public health goal (not for medical diagnostic purposes; rapid antigen tests are less accurate if you apply a standard PCR), these tests become extremely accurate, and can help us control the spread of the disease. But on the other hand, under no circumstances can you start implementing antigen tests without providing confirmatory tests along with them to avoid false positives: once someone tests positive, they are not called positive; at that time a confirmation test is performed (3).
Thus, antigen testing is predicted to change the fight against the pandemic. Rapid antigen testing has been reported to be highly sensitive in detecting the presence of SARS-CoV-2 in nasal or nasopharyngeal swabs from symptomatic and asymptomatic individuals. Diagnostic performance of the test is particularly good in samples with viral loads associated with a high risk of viral transmission (Ct <25), which show high positive and negative predictive values even when a prevalence as low as 5% is assumed (5).
In a community transmission scenario, what we want to know is whether a patient is contagious. The antigen test is the most powerful tool we have to find out. "We can give up that sensitivity to win where we had a huge problem, which was the time it took to communicate positives and isolate." Rapid antigen tests would perform particularly well in those cases, "associated with a high risk of transmission." "SARS-CoV-2 can be transmitted before symptoms appear, so by the time a symptomatic case is detected, it may have infected others - which means that conventional testing and tracing is always playing catch" (6).
The indications of numerous international organizations have meant that antigen tests are being used in symptomatic cases, where they were better studied by the manufacturers (7). But some studies suggest that they could also be used for close contacts without symptoms (5, 7).
However, mass testing is still one piece to fit the puzzle. In several countries, from Spain to India to the United Kingdom, massive screening has been done to find positives in places such as a university campus or a neighborhood. If thousands of people are tested, some will be found infected. But it is still a challenging strategy. Firstly, for the false positives; some of the people who test positive are not actually infected - between 10 and 150 people for every 10,000 tested, depending on the specificity of the antigen test and the prevalence of the disease (8). For example, in Slovakia (9) they have tested two thirds of its population and quarantined the 57,000 people who tested positive, although a part will not have the virus. It is not clear whether the screenings performed so far have worked well, but it is possible that in the coming months the efficacy of the use of antigens for mass testing will improve. There is even talk of individual use; almost a home use. Having cheap, fast and self-executing antigens, they may become mandatory for risky activities: travelling by plane, dining in a restaurant or hanging out with a group of friends for a few days. Even if the vaccine arrives, the virus will not disappear completely and it will continue to be important to protect ourselves in the best possible way (10).
Medical decisions are taken in a framework of uncertainty. Probability of disease moves between diagnostic threshold, below which no further tests are needed, and therapeutic threshold, above which we don’t need further tests to justify treatment (11).
REFERENCES
1.-Stone J. Re: Mass testing for covid-19 in the UK-The "silent driver"of the COVID-19 pandemic. BMJ 2020;371:m4436. https://www.bmj.com/content/371/bmj.m4436/rr-11
2.-WHO. Q&A: How is COVID-19 transmitted? 14 July 2020. Feature story. Ha Noi. WHO. https://www.who.int/vietnam/news/detail/14-07-2020-q-a-how-is-covid-19-t...
3.-Wallace-Wells D. Rapid Antigen Tests Are Effective, Cheap, and Could Quash the Pandemic Within Weeks (In Theory). INTELLIGENCER 2020; DEC. 4. https://nymag.com/intelligencer/2020/12/how-rapid-antigen-tests-could-en....
4.-Larremore DB, Wilder B, Lester E, et al. Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening. Sci Adv 2020; eabd5393. https://advances.sciencemag.org/content/early/2020/11/20/sciadv.abd5393.1
5.-Alemany A, Baro B, Ouchi D, et al. Analytical and Clinical Performance of the Panbio COVID-19 Antigen-Detecting Rapid Diagnostic Test. MedRxiv 2020.10.30.20223198. https://doi.org/10.1101/2020.10.30.20223198
6.-Kucharski A. What are the benefits/limitations of mass testing certain populations for SARS-CoV-2 regardless of symptoms? Twitter 2020; 8 sept. https://twitter.com/AdamJKucharski/status/1303245757932343296
7.-THE EUROPEAN COMMISSION. COMMISSION RECOMMENDATION of 18.11.2020 on the use of rapid antigen tests for the diagnosis of SARS-CoV-2 infection. https://ec.europa.eu/health/sites/health/files/preparedness_response/doc...
8.-Shuren J, Stenzel T. Covid-19 Molecular Diagnostic Testing — Lessons Learned. N Engl J Med 2020. https://www.nejm.org/doi/full/10.1056/NEJMp2023830?query=TOC
9.-Shotter J. Slovakia’s mass coronavirus testing finds 57,500 new cases. The Financial Times 2020; NOVEMBER 10. https://www.ft.com/content/6d20007c-25ad-4d1a-b678-591acaa57df9
10.-CORONAVIRUS COVID-19. [Isolate fast and cut infections: how antigen testing is changing the pandemic]. El País 2020. https://elpais.com/sociedad/2020-12-05/aislar-rapido-y-cortar-contagios-...
11.-Molina Arias M. [Characteristics of diagnostic tests ]. [Article in Spanish]. Rev Pediatr Aten Primaria 2013; 15(58). http://scielo.isciii.es/scielo.php?script=sci_arttext&pid=S1139-76322013...
Competing interests: No competing interests
Dear Editor
I am once again most grateful to Jose L Turabian [1]. I have one or two reservations. I am not, of course, a medical doctor or scientist but as I understand it the classic means of transmission of an infectious respiratory disease would be through coughing and sneezing, and someone who is not coughing and sneezing - being asymptomatic - must surely be much less of a hazard than someone who is. I also wonder, given the vexxed issue in this episode of false positives how strong is the evidence base?
[1] Jose L Turabian, ‘ Re: Mass testing for covid-19 in the UK-The "silent driver"of the COVID-19 pandemic’, 6 December 2020, https://www.bmj.com/content/371/bmj.m4436/rr-9
Competing interests: AgeofAutism.com, an on-line daily journal, concerns itself with the potential environmental sources for the proliferation of autism, neurological impairment, immune dysfunction and chronic disease. I receive no payment as UK Editor. I also moderate comments for the on-line journal ‘The Defender’ for which I am paid. I am also a member of the UK Medical Freedom Alliance
Dear Editor,
I am grateful to John Stone (1, 2) that he gives me the opportunity to include a few other references (for the literature review a pragmatic approach was used with a non-systematic or opportunistic narrative review) in relation to the alleged responsibility of being a "silent driver" of the COVID-19 pandemic, which I did not initially cite (3).
Certainly the paper by Cao et al. ("A total of 1,174 close contacts of the asymptomatic positive cases were traced, and all tested negative for COVID-19") (4) is important, if only the exception which proves the rule. The researchers have said that their findings did not show that the virus could not be transmitted by asymptomatic carriers and did not suggest that their findings were generalizable. They said that strict measures, such as the use of masks, hand washing, social distancing and confinement, managed to reduce the virulence of SARS-CoV-2 in Wuhan and that asymptomatic people in Wuhan may have low viral loads. This means that the finding cannot be applied to countries where outbreaks have not been successfully controlled. There is a lot of evidence elsewhere showing that people infected with COVID-19 can be temporarily asymptomatic and infectious, before developing symptoms (5).
We must bear in mind that what has been accepted so far is: 1) people are really highly infectious from the beginning and that emphasizes that we need much faster tests and immediate results in order to prevent further transmission; 2) most studies agree that baseline viral loads are similar between symptomatic and asymptomatic people; 3) asymptomatic people have a shorter viral shed, which means that they can be infectious but for a shorter period; 4) transmission in asymptomatic people generally occurs between households (6, 7).
In case it can be useful in this reflection, I write below the sentence of my quick answer that was without references, adding them now.
These asymptomatic infections act as a "silent driver" of the pandemic (8). The infectivity during the incubation period for COVID-19 is a big challenge for controlling the disease (9). The actual public health burden of this massive group of asymptomatic patients interacting in the community suggests that a considerable part of transmission events stem from asymptomatic transmissions (8). Higher levels of virus can occur in presymptomatic and asymptomatic patients. Viral loads have been reported to be similar between asymptomatic (including presymptomatic) and symptomatic patients. Furthermore, viral loads tend to decrease more slowly in asymptomatic patients (10). Presymptomatic and asymptomatic transmission significantly reduces the effectiveness of control measures that start with the onset of symptoms, such as isolation and follow-up of contacts (11). Additionally, asymptomatic infection can be associated with slight changes in biochemical and inflammatory variables and subclinical pulmonary abnormalities can occur, detected by computed tomography (12, 13).
Finally, I sincerely thank John Stone for his effort to promote and share critical reflection.
REFERENCES
1.-Stone J. Rapid Response: Re: Mass testing for covid-19 in the UK. BMJ 2020;371:m4436. https://www.bmj.com/content/371/bmj.m4436/rr-6
2.-Re: Mass testing for covid-19 in the UK-Some of the references that were left out. BMJ 2020;371:m4436. https://www.bmj.com/content/371/bmj.m4436/rr-8
3.-Turabian JL. Mass testing as another approach in the management of asymptomatic cases of covid-19. Rapid response to: Mass testing for covid-19 in the UK. BMJ 2020;371:m4436. https://www.bmj.com/content/371/bmj.m4436/rr-5
4.-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. https://www.nature.com/articles/s41467-020-19802-w
5.-Griffin S. Covid-19: Asymptomatic cases may not be infectious, Wuhan study indicates. BMJ 2020; 371:m4695. https://www.bmj.com/content/371/bmj.m4695?utm_source=etoc&utm_medium=ema...
6.-Kozlov M (2020) Q&A: COVID-19 Infectiousness Peaks Early in Sickness, Study Shows. The Scientist; Nov 23. https://www.the-scientist.com/news-opinion/qa-covid-19-infectiousness-pe...
7.-Cevik M, Tate M, Lloyd O, Maraolo AE, Schafers J, Ho A. SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis. Lancet Microbe 2020. https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(20)30172-5/fulltext
8.-Nogrady B (2020) What the data say about asymptomatic COVID infections. People without symptoms can pass on the virus, but estimating their contribution to outbreaks is challenging. Nature; 18 NOVEMBER. https://doi.org/10.1038/d41586-020-03141-3
9.-Ping Yu, Jiang Zhu, Zhengdong Zhang, Yingjun Han, A Familial Cluster of Infection Associated With the 2019 Novel Coronavirus Indicating Possible Person-to-Person Transmission During the Incubation Period, The Journal of Infectious Diseases, Volume 221, Issue 11, 1 June 2020, Pages 1757–1761, https://doi.org/10.1093/infdis/jiaa077
10.-Lee S, Kim T, Lee E, et al. (2020) Clinical course and molecular viral shedding among asymptomatic and symptomatic patients with SARS-CoV-2 infection in a community treatment center in the Republic of Korea. JAMA Intern Med. https://doi.org/10.1001/jamainternmed.2020.3862)
11.-He X, Lau EHY, Wu P, et al. (2020) Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med; 26: 672–5. https://doi.org/10.1038/s41591-020-0869-5
12.-Oran DP, Topol EJ (2020) Prevalence of Asymptomatic SARS-CoV-2 Infection: A Narrative Review. Ann Intern Med; 173: 362-7. https://www.acpjournals.org/doi/10.7326/M20-3012
13.-Pan Y, Yu X, Du X, et al. (2020) Epidemiological and Clinical Characteristics of 26 Asymptomatic Severe Acute Respiratory Syndrome Coronavirus 2 Carriers. J Infect Dis; 221(12): 1940-7. https://doi.org/10.1093/infdis/jiaa205
Competing interests: No competing interests
Dear Editor
I am grateful to Jose Turabian [1] but he has missed the crux of my question which is not about the numbers of the asymptomatic patients but their alleged responsibility being “ a“silent driver” if the pandemic” [2], hence my citation of the paper by Cao et al.
[1] Jose L Turabian, ‘ Re: Mass testing for covid-19 in the UK-Some of the references that were left out’, 4 December 2020, https://www.bmj.com/content/371/bmj.m4436/rr-7
[2] Jose L Turabian, ‘ Mass testing as another approach in the management of asymptomatic cases of covid-19’, 23 November 2020, https://www.bmj.com/content/371/bmj.m4436/rr-5
[3] Cao et al, ‘Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China’, Cao et al, 20 November 2020, https://www.nature.com/articles/s41467-020-19802-w
Competing interests: AgeofAutism.com, an on-line daily journal, concerns itself with the potential environmental sources for the proliferation of autism, neurological impairment, immune dysfunction and chronic disease. I receive no payment as UK Editor. I also moderate comments for the on-line journal ‘The Defender’ for which I am paid. I am also a member of the UK Medical Freedom Alliance
Dear Editor,
John Stone (1) is correct in saying that I do not provide any sources for a sentence in my quick response (2). I deliberately omitted references for not lengthening the text, and assuming they were in the public domain. But perhaps those sources are really worth pointing out to avoid misunderstandings. So I rewrite the same previously posted sentence with some of the references I left out:
“The number of asymptomatic SARS-CoV-2 infections, in which people do not show any symptoms, remains questionable and uncertainty remains about how much they have contributed to the pandemic. It has been claimed that up to 40% of infections can be asymptomatic (3). In a study that analyzed almost a hundred studies on this subject, it was estimated that the number of patients who did not develop symptoms during the entire infection was around 20%, with a wide range that ranged from 3 to 67%; if the population bias is analyzed, the percentage of asymptomatic patients rose to 31% (4). These data are not far from what seroprevalence studies say: one third of patients do not develop symptoms (5). On the other hand, another review, of more than 2,500 studies, found percentages of asymptomatic patients between 4 and 41%, and concluded that the real figure was between 14 and 20% (6).”
REFERENCES
1.-Stone J. Rapid Response: Re: Mass testing for covid-19 in the UK. BMJ 2020;371:m4436. https://www.bmj.com/content/371/bmj.m4436/rr-6
2.-Turabian JL. Mass testing as another approach in the management of asymptomatic cases of covid-19. Rapid response to: Mass testing for covid-19 in the UK. BMJ 2020;371:m4436. https://www.bmj.com/content/371/bmj.m4436/rr-5
3.-Oran DP, Topol EJ Prevalence of Asymptomatic SARS-CoV-2 Infection: A Narrative Review. Ann Intern Med 2020; 173: 362-7. https://www.acpjournals.org/doi/10.7326/M20-3012
4.-Buitrago-Garcia D, Egli-Gany D, Counotte MJ, et al. Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis. Plos Medicine 2020. https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1...
5.-Pollán M, Pérez-Gómez B, Pastor-Barriuso R, et al. Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study. Lancet 2020. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31483-5/fulltext
6.-Byambasuren O, Cardona M, Bell K, et al. Estimating the extent of asymptomatic COVID-19 and its potential for community transmission: systematic review and meta-analysis. MedRxiv; 2020.05.10.20097543. https://doi.org/10.1101/2020.05.10.20097543.
Competing interests: No competing interests
Dear Editor
Without offering any source Jose Turabian states [1]:
“Probably 20-30% of infections are asymptomatic. These asymptomatic infections act as a "silent driver" of the pandemic. The actual public health burden of this massive group of asymptomatic patients interacting in the community suggests that a considerable part of transmission events stem from asymptomatic transmissions. Higher levels of virus can occur in presymptomatic and asymptomatic patients.”
But I also notice from the abstract of a new study from Wuhan [2]:
“No new symptomatic cases and 300 asymptomatic cases (detection rate 0.303/10,000, 95% CI 0.270–0.339/10,000) were identified. There were no positive tests amongst 1,174 close contacts of asymptomatic cases.”
I doubt whether we have ever had an epidemic before in which there has been such an interest in the asymptomatic.
[1] Jose L Turabian, ‘ Mass testing as another approach in the management of asymptomatic cases of covid-19’, 23 November 2020, https://www.bmj.com/content/371/bmj.m4436/rr-5
[2] Cao et al, ‘Post-lockdown SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China’, Cao et al, 20 November 2020, https://www.nature.com/articles/s41467-020-19802-w
Competing interests: AgeofAutism.com, an on-line daily journal, concerns itself with the potential environmental sources for the proliferation of autism, neurological impairment, immune dysfunction and chronic disease. I receive no payment as UK Editor
Dear Editor,
The effectiveness of control measures depends on the role of asymptomatic people in the transmission of SARS-CoV-2. Probably 20-30% of infections are asymptomatic. These asymptomatic infections act as a "silent driver" of the pandemic. The actual public health burden of this massive group of asymptomatic patients interacting in the community suggests that a considerable part of transmission events stem from asymptomatic transmissions. Higher levels of virus can occur in presymptomatic and asymptomatic patients. Viral loads have been reported to be similar between asymptomatic (including presymptomatic) and symptomatic patients. Presymptomatic and asymptomatic transmission significantly reduces the effectiveness of control measures that start with the onset of symptoms, such as isolation and follow-up of contacts. Additionally, asymptomatic infection can be associated with slight changes in biochemical and inflammatory variables and subclinical pulmonary abnormalities can occur, detected by computed tomography.
In this scenario, how to manage “silent” (asymptomatic) cases? Identify the points where asymptomatic cases are occurring by approaching the situation from a comprehensive perspective. This inevitably includes (in addition to other approaches such as: test system, trace and public health measures; the strict follow-up of negative cases as well as positive ones; and backward follow-up of the contacts of positive cases, looking for the source of a new case together with the contacts of that person) massive and opportunistic tests for the detection of general and specific populations: rapid response tests for COVID-19 available to everyone, specifically for those without symptoms, performed as mass population screening, to certain groups such as health workers and students, such as opportunistic detection in the general practitioner's office, and even in concerts, in the cinema, in large commercial surfaces, or at home self-administered by anyone (maintaining the rest of public health measures: masks, distancing , capacity limitation, hand washing, mobility limitation). In this approach, even with the possible errors, most of the possible vectors of the disease would be detected.
However, the strategy of mass testing has been criticized (1). On the one hand, due to its high rate of false negatives; that is, it does not have a high enough sensitivity to rule out COVID-19. Thus, it can give people the mistaken assurance that, "at least for a limited time, they are unlikely to have the virus and that they are at low risk of transmitting it to others" (2). But, the asymptomatic patient with a false negative that assumes false security and puts others at risk, would also incur the same role of not being infected and would also put others at risk, without proof; thus we would be in Pascal's wager, an argument in philosophy presented by the seventeenth-century French philosopher, Blaise Pascal (1623–1662): a rational person should choose to believe in God, because, if it exists, the reward - eternal glory - would be infinite. And if it did not exist, it does not matter much if one chose one or the other belief) (3).
On the other hand, it has been pointed out that the frequency of SARS-CoV-2 tests at the population level is more important than the sensitivity of the test in controlling the pandemic. Effective detection is highly dependent on test frequency and reporting speed, and only marginally improves with high test sensitivity. Therefore, screening must prioritize accessibility, frequency, and time between sample and response; the analytical limits of detection must be secondary (4).
It is also said that many asymptomatic people who test positive for COVID-19 on the rapid test are probably relatively non-infectious. Although avoiding risk, even a small risk, is possibly a wise decision. Likewise, it is said that half of asymptomatic cases can develop symptoms later and be detected at that time, without the need for a rapid test (5). But, the presymptomatic stage seems to be the most contagious (6); and in the end that patient would also require a PCR test for diagnosis. In any case, users of these tests should certainly be explained the erroneous belief that they "accurately detect infectivity" and that their negative result does not imply that they are released from the restrictions.
The criticisms of mass testing seem totally correct, but perhaps they are summarized in cost problems, and it may be that they do not contemplate all the necessary approaches to manage asymptomatic (silent) cases of COVID-19. From this comprehensive perspective, it seems that the advantages outweigh the problems as an approach to asymptomatic patients, and the initial acceptability of these tests is high. Rapid, cheap and frequent mass testing, will likely be a vital tool to help control COVID-19 and make life more normal by cutting the chains of transmission (7).
REFERENCES
1.-Gill M,Muir G. Mass testing for covid-19 in the UK. BMJ 2020; 371: m4436. https://www.bmj.com/content/371/bmj.m4436?ijkey=0455b38eeb03e1501a4f10f1...
2.-Mahase E. Covid-19: Innova lateral flow test is not fit for “test and release” strategy, say experts. BMJ 2020; 371: m4469. https://www.bmj.com/content/371/bmj.m4469?int_source=trendmd&int_medium=...
3.-Pascal's wager. From Wikipedia, the free encyclopedia.[accessed November 22, 2020].https://en.wikipedia.org/wiki/Pascal%27s_wager
4.-Larremore DB, Wilder B, Lester E, et al. Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening. Sci Adv 2020; eabd5393. https://advances.sciencemag.org/content/early/2020/11/20/sciadv.abd5393.1
5.-McNamara D. About 80% of Asymptomatic People WithCOVID-19 Develop Symptoms, Medscape 2020; Sep 28. https://www.medscape.com/viewarticle/938195?nlid=137615_4663&src=WNL_mdp...
6.-He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med 2020; 26: 672–5. https://doi.org/10.1038/s41591-020-0869-5
7.-Iacobucci G. Covid-19: Government ramps up “Moonshot” mass testing. BMJ 2020; 371: m4460. https://www.bmj.com/content/371/bmj.m4460?int_source=trendmd&int_medium=...
Competing interests: No competing interests
Dear Editor,
We are grateful for I Strachan pointing out that we have misquoted the false positive rate (FPR) for the Innova test, as measured in the Porton Down/Oxford interim evaluation. It should be 0.4% rather than 0.6%, but not, as she proposes, 0.06%. As she points out, 0.06% is the rate measured in the most ideal lab conditions, a measure of efficacy. The conditions most like those in the field in Liverpool are those of the Covid-19 testing centre, where the FPR is given as 0.4%, a better reflection of true effectiveness.
The substantive point is unchanged: there will be almost twice as many false positives as true positives at a prevalence of 400/100000, and if the prevalence halves, more than three times.
Competing interests: No competing interests
Dear Editor
Why did Liverpool not use the same LFT tests as Slovakia?
Mass Testing – What do we know?
Based on one weeks’ worth of data at Liverpool.
528 Positives
115,657 total tests.
Of which 69,643 were conducted with the Innova TriedandTested LFT.
Early in the testing, symptomatic and asymptomatic donors were not properly segregated.
At the centre itself, there was demarcation, but outside of that people mixed freely before the formation of the two lines.
Therefore, even when the 528 positives were standing in the correct line, i.e. asymptomatic donors, it is obvious from the pictures and video of the lines in Liverpool, that these same asymptomatic donors were within 2 metres of other donors who were negative for the virus.
What happens to these people in terms of the NHS Track and Trace App?
The positive asymptomatic donors are of course identified by their positivity of the test result.
If their phones were within 8 feet of other phones using the App, then the owners of these phones, (asymptomatic and negative) would be required to self-isolate.
We would then have the situation, that negative donors, who are in fact tested negative as well, are told to self-isolate because they have been standing in close proximity to a test positive donor.
If these negative asymptomatic donors had not bothered to submit to mass testing, then they would not have had the opportunity, (or rather misfortune) to be standing beside an asymptomatic donor who is subsequently tested positive with the LFT and subsequently confirmed as a true positive by PCR.
Unintended community transmission by standing in a queue to be tested.
Obvious questions.
Of the 528 positives, how many were subsequently confirmed positive by PCR?
Of these true positives how many will/have self-isolated?
How many of their close contacts, (as per above and their family/work colleagues) has Track and Trace contacted. How many of these people will self-isolate?
How many of the 115657 are repeat testers? (What encourages previously tested negative donors to stand in the rain a few days later to be tested again?)
If 115.657 represents approximately 12% of the greater Liverpool metro area, is that percentage after a week’s worth of testing hitting the goal?
Competing interests: No competing interests
Evidence of asymptomatic spread is insufficient to justify mass testing for Covid-19
Dear Editor,
Whilst we would take issue with Lateral Flow tests being the main culprit, Mike Gill is absolutely correct to criticise mass testing programmes.
His ire should really be directed, though, at PCR testing. Data from PCR testing – for which there is no proper determination of an end-to-end operational false positive rate – has almost exclusively dictated tier restrictions and lockdown policy in the UK.
PCR’s fingerprints can in fact be found all over the entire global response to this pandemic. Testing with Lateral Flow, other antigen tests and bedside PCR tests are all finding far fewer cases than diagnosed by PCR testing. Even a low sensitivity for all these other tests could not account for the size of the discrepancy.
Mass testing and accompanying harmful lockdown policies are justified on the assumption that asymptomatic transmission is a genuine risk. Given the harmful collateral effects of such policies, precautionary principle should result in a very high evidential bar for asymptomatic transmission being set. However, the only word which can be used to describe the quality of evidence for this is woeful.
It is important to carefully distinguish purely asymptomatic (individuals who never develop any symptoms) from pre-symptomatic transmission (where individuals do eventually develop symptoms). To the extent that the latter phenomenon - which has in fact happened only very rarely - is deemed worthy of public health action, appropriate strategies to manage it (in the absence of significant asymptomatic transmission) would be entirely different and much less disruptive than those actually adopted.
Many early studies which purported to demonstrate the phenomenon of asymptomatic transmission were from China, yet the fact that Chinese studies are only published following government approval must bring into question their reliability (1). Nevertheless, the high volume of these studies spawned significant salience of the issue within the medical community, and an assumption of the likelihood of asymptomatic transmission being an important contributory factor. There then followed a number of meta-analyses examining the issue of asymptomatic transmission which tended to aggregate and give equal weight to studies regardless of origin or quality. In this way, these meta-analyses, given undue credibility by their association with reputable universities, amplified minimal evidence of asymptomatic spread to an importance the data did not warrant.
As reported in a manuscript submitted to this journal and also to medRvix on 16 Dec 2020 (the latter available for download shortly), we examined the papers most frequently cited in support of the existence of asymptomatic transmission. Even despite our criticisms of the sources of the data above, we did in fact find only 6 case reports of viral transmission by people who throughout remained asymptomatic, and this was to a total of 7 other individuals, however all of these were in studies with questionable methodology.
Moreover in all these studies, confirmation of “cases” was made via PCR testing without regard to the possibility that any of the cases found might be false positives. The case numbers found, are, in any event extremely small and certainly not sufficient to conclusively determine that asymptomatic transmission is a major component of spread.
It is also notable that, in what would seem to represent an abrupt volte face by the CCP, a further (presumably government-approved) study from China was recently published (2) which entirely contradicts the earlier conclusions regarding the phenomenon of asymptomatic transmission, which had been driven by Chinese data in particular, early in the pandemic.
Some might conclude that that study lacks the credibility one might expect for a paper published in Nature; it is claimed, for example, that they PCR-tested 92% of Wuhan’s population (~10m individuals) over a 19-day period at the end of May, and found just 300 positive PCR tests, implying a FPR of no greater than 0.003%. Further, it is claimed that while 100% of the 300 PCR positive cases were asymptomatic, there were zero symptomatic PCR positive cases out of ~10m tested during a period only a few weeks after the epidemic had peaked in Wuhan.
If this seems incredulous, then surely that has serious implications for the way in which earlier studies from China - data from which formed a significant part of the worldwide evidence base for asymptomatic transmission - should be regarded.
Jonathan Engler MBChB LLB
Clare Craig BM BCh FRCPath
Silver, Andrew, and David Cyranoski. 2020. “China Is Tightening Its Grip on Coronavirus Research.” Nature 580 (7804): 439–40.
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 11, 5917 (2020). https://doi.org/10.1038/s41467-020-19802-w
Competing interests: No competing interests