Covid-19: the problems with case counting
BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m3374 (Published 03 September 2020) Cite this as: BMJ 2020;370:m3374Read our latest coverage of the coronavirus outbreak
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Dear Editor
Arnaud Chiolero writes:
"Overdiagnosis of Covid-19 does however not imply overdetection of SARS-CoV-2. On the contrary. Detection of all infections and tracing of close contacts is key to stop spread and contain outbreaks.. In that sense, there is no overdetection because it is useful, at a population level, to detect all persons with the virus."
While he is mindful of the risk of over-diagnosing COVID-19 it is till questionable how useful the tracking of infection is if this is used by our government to alarm people (who might not be so pre-armed about subtlties of definition) and it generates lots of false positives i.e. if we do not test at least we will at least not get false results, or results which are impossible to interpret. The speculative routine screening of healthy citizens for viruses they might be carrying is a dystopian nightmare which would of course prevent life ever returning to normal - as if the social cost of the present misadventure was not bad enough.
Arnaud Chiolero, 'Surveillance Bias and Overdiagnosis of Covid-19', 6 September 2020, https://www.bmj.com/content/370/bmj.m3374/rr-1
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
A second wave of covid-19 could have started in several European countries [1]. Is that however a wave of the same disease? While it is apparently - besides some genetic changes - the same virus, the number of hospitalizations and deaths is surprisingly small in regard to the number of people found to be infected by the virus. How is that possible? Surveillance bias and overdiagnosis help understand the current trend.
First, a surveillance bias explains the changing epidemiology of covid-19. Such a bias occurs when a condition is searched with differential intensity according to the setting of care or the type of patients [2, 3]. Covid-19 infection is a condition sensitive to the density of inquiry and screening activities. Currently, the tests to detect the SARS-CoV-2 are much more frequently done in many countries compared to the period of the first wave. Further, the patients tested are younger than previously. As a result, the typical covid-19 cases diagnosed have changed, moving from relatively old people with symptoms, tested positive, and at high risk of complications to younger low risk people with a polymerase chain reaction (PCR) positive result alone, regardless of symptoms [1].
Second, and this is related to the first point, one could argue that Covid-19 is overdiagnosed. Overdiagnosis occurs when people are diagnosed with a condition not associated with a substantial risk of adverse outcomes or for which no intervention reduces substantially this risk [3, 4]. Counting asymptomatic or paucisymptomatic cases of SARS-CoV-2 infection as Covid-19 cases is a form of overdiagnosis.
Overdiagnosis of Covid-19 does however not imply overdetection of SARS-CoV-2. On the contrary. Detection of all infections and tracing of close contacts is key to stop spread and contain outbreaks [5]. In that sense, there is no overdetection because it is useful, at a population level, to detect all persons with the virus.
References
1. Mahase E. Covid-19: the problems with case counting. BMJ 2020;370:m3374
2. Haut ER, Pronovost PJ. Surveillance bias in outcomes reporting, JAMA, 2011;305: 2462-3
3. Chiolero A, Santschi V, Paccaud F. Public health surveillance with electronic medical records: at risk of surveillance bias and overdiagnosis. Eur J Pub Health 2013; 23(3): 350-1.
4. Moynihan R, Doust J, Henry D. Preventing overdiagnosis: how to stop harming the healthy, BMJ 2012; 344: e3502
5. Baraniuk C. Covid-19 contact tracing: a briefing. BMJ 2020; 369: m1859
Competing interests: No competing interests
Dear Editor,
The article from Elizabeth Mahase is timely and pointful.
I should caution your readers against the chart which compares test positivity percentages in the different pillars (RHS) with the numbers of cases (LHS). Because of the high rate of Pillar 1 positives at the height of the epidemic, over 40%, the scale on the RHS has to accommodate values up to 48%. This is completely inappropriate to the making of any judgements about what has been going on in the last three months, where typical ratios have been closer to 0.048%.
Jeremy Stone
Competing interests: No competing interests
Dear Editor
I wish to make a formal proposal on the nomenclature used in the coronavirus pandemic.
At present the terms coronavirus, SARS-CoV-2 and Covid-19 are used interchangeably, and this is causing confusion and muddled thinking.
There is no problem with counting Covid-19 cases, as these are admitted to hospital. There is, however, a problem with counting SARS-CoV-2 cases, which is actually what this article is discussing.
SARS-CoV-2 is a novel coronavirus. Covid-19 is the serious illness, due to a cytokine storm syndrome (CSS), which is consequent upon infection with SARS-CoV-2. Thus coronavirus and SARS-CoV-2 may reasonably be used interchangeably but Covid-19 represents a specific outcome which is a subset of those infected with SARS-CoV-2. Indeed the features of Covid-19 are not even specific to SARS-CoV-2 infection, as cytokine storms occur with numerous triggers (and indeed there is confusion here, because Macrophage Activation Syndrome (MAS) and Haemophagocytic lymphohistiocytosis (HLH) are clinically synonymous with CSS). People are not testing positive for Covid-19; they are testing positive for infection with SARS-CoV-2. Explanations for the continuing rise in positive tests are several; more widespread testing is one, change in disease severity is another, but the rise is not causing a concomitant rise in hospital admissions. Therefore it may be irrelevant.
If we start talking about the numbers of positive tests for SARS-CoV-2, and publish data on the numbers of cases of Covid-19, clearly differentiating the two, I suspect we will find that the mismatch will allay any panic over the prospect of a second wave, which won't signify if an apparent rise in infection rate fails to translate into severe disease.
Competing interests: No competing interests
COVID-19 Statistics: What does it really all mean?
Dear Editor
The whole world today is glaring at two most important statistics: number of corona virus cases and corona virus related deaths. A country’s economic growth, success or failure of healthcare policies, as well leadership is being speculated about and assessed mainly on these figures.
Every morning, new figures either bring about a sigh of relief or a new ray of hope or they become a cause for anger, frustration and hopelessness.
But the real question is, should we really be counting and if yes, till how long? What does SARS COV-2 positive really mean? We know by now that at least one third of a population tested positive for SARS COV-2 are asymptomatic. However, are the positive tests clinically relevant? It has been demonstrated that a positive test may also mean picking up dead virus genetic material which is clinically inert. This is in some ways like colonization of MRSA and Helicobacter Pylori that does not have much clinical significance as they do not pose a considerable threat to health and wellbeing.
So, merely the presence of SARS COV-3 genetic material in someone does not mean that such an individual is infected.
Therefore, there should be other protocols to be followed and tests performed in order to confirm active infection. This would greatly help in triage and go a long way in further management of COVID-19. This strategy is also likely to have significant impact on saving resources, as well as avoiding unnecessary fear, apprehension and panic amongst the general public.
Dr Syed Raza
MD, FRCP (Edin.), CCT
Consultant Cardiologist and Physician
Awali Hospital, Bahrain
Competing interests: No competing interests