PCR testing for Covid-19: Quo Vadis?

By Dr. Sumedha S. Amarasekara

I am on ‘Ada Derana news information texts’ and almost every day I get an ‘UPDATE: a three digit number tested positive for Covid-19. All are close contacts of earlier patients’. The Island (4.12.2020) reports that we have now crossed the 10,000 mark of Covid-19 cases in the Colombo District. What exactly does this increasing number of positive cases mean? How valid is our rationale for PCR testing? Does testing close contacts make an impact on the management of Coivd-19? Can we afford all this testing as a country?

I strongly urge everyone to view the U-tube presentation of Prof. Malik Peries (Hong Kong) as an expert and world authority on Covid-19 being interviewed by Dr. Ananda Wijewickrama (Sri Lanka) and Dr. Chamila De Silva (Sri Lanka): Myths and fallacies vs. Science and Truth of Covid-19. (https://www.youtube.com/embed/PthrJpAilQ0). Though admittedly the discussion did not revolve around the validity and rationale for PCR testing, the necessary evidence to do so can be arrived at by analyzing the data from two of the slides presented by Dr. Malik Peries – a testament to the title of the presentation.

The slide, ‘infectiousness profile of SARS-CoV-2’, clearly illustrates that the virus is most infective one day prior to that person developing symptoms. Thereafter the ability of the virus to infect diminishes. After the first week of developing symptoms the ability of the Covid-19 to infect another person becomes very low.

The other slide, ‘Duration of infectiousness – viral RNA load, virus culture vs. days illness’ correlates a positive PCR result against the infectiousness of the virus. This slide confirms that persons are no longer infective after day 10. More importantly this slide demonstrates that the PCR test can remain positive in some cases even beyond two months – when the person is no longer infective and is in fact cured.

With these scientifically proven facts, let us now look at the value of PCR testing in conjunction with what we already know about this virus and the PCR test. With regards to the virus we know that, in the vast majority Covid-19 infection is asymptomatic (or very mild) while a pneumonia is encountered in the remainder. Most of these patients (with pneumonia) will recover and only a very few of these cases will end in death. In regards to the PCR test we know, that it is not infallible i.e. a single negative result after exposure to the virus, does not exclude the possibility of one not having the virus.

First let us consider a symptomatic patient.i.e. high fever, breathing difficulty, cough, etc… strongly suggestive of having being infected by the Covid-19 virus. The PCR test has the greatest value in this case as it can confirm that he/she has got Covid-19 and is infective. He/She needs to be isolated, admitted for treatment if need be and through contact tracing all contacts should be kept in quarantine. If the initial PCR test is negative, an experienced clinician needs to be involved to determine what further action/repeated testing needs to be done.

If a symptomatic patient after repeated/adequate testing remains negative, then the conclusion will need to be made that, he /she has not got Covid-19 and accordingly his/her contacts need not be quarantined. It follows that if the contacts are still to be quarantined, then one seriously needs to question the purpose of testing in the first place. In which case you might as well quarantine all contacts of any patient who presents with symptoms suggestive of Covid-19 infection without spending further money and resources on testing!

Secondly, let us consider those who are in quarantine (close contacts). A positive result could either be, one is yet to be infective, currently infective-but asymptomatic or already has got better and is no longer infective. On the other hand a negative result does not exclude the possibility of having a Covid-19 infection. Therefore as one can see there is no real advantage/validity of testing anyone in quarantine. What needs to be done is complete the quarantine. According to the current advice and as demonstrated by the slides after 10 days in quarantine one is safe to come in to the community – no testing is needed.

Thirdly, let us consider a random test. Now once again as documented above, a positive result could mean that either he/she is yet to develop the disease, has it and is asymptomatic or has got over it. If one were to develop symptoms then the subsequent management becomes a fairly straightforward process. But what if one does not develop symptoms? The chances of this happening are invariably higher as it is a known fact that almost 70 % or more of those who have the disease are ‘asymptomatic’ and also that those who have got over the disease can be PCR positive beyond two months. As the disease spreads through the community the latter group is going to expand exponentially as well. This is where science and economics of the country need to come together. How much random testing are we to do? And more importantly what is the rationale behind this testing? If someone tests positive, what should we do? Are we to then quarantine all of his/her contacts? Lockdown and isolate areas? How valid is this scientifically? And more importantly how much money can we afford to spend on this?

When one considers that a PCR test done in the government sector is estimated at around Rs. 6000 and that the monetary relief provided to an entire family that is in a lockdown/quarantine area for a month is Rs.5000; one could argue that it would be better to provide each member/family in quarantine Rs.5000 instead of testing them at Rs. 6000 individually! As can be seen from the above discussion this actually would be logically a more scientific (and economical) approach.

The ultimate criteria that determines how well a country is managing the crisis of Coivd-19 is the number of deaths that account for this disease. In this regard (examining the statistics of different countries) two indices can be used: case fatality rate and a death rate for the population. The former records the number of deaths in relation to the number of cases. The latter is the number of deaths according to the population of the country. In interpreting this data what needs to be grasped is that any person that tests positive on a PCR is considered as a case.

At the time of writing this article according to the John Hopkins University mortality analyses (https://coronavirus.jhu.edu/data/mortality) Taiwan has the lowest death rate of 0.03/ 100k population. The case fatality rate in Taiwan is 1%. The country that has the highest death rate is Belgium, which is 148.06/100k population. The case fatality rate in Belgium is 2.9%. The highest case fatality rate is in Yemen at 28%. However, the corresponding death rate is only 2.18/100k population. On the other hand the lowest case fatality rate is in Qatar at 0.2% with a corresponding death rate of 8.59/100k population. What can be seen when one reviews this data, is that the case fatality rate has no bearing on the death rate. In other words the more testing that is done, the lower the case fatality rate, which has no actual bearing on the overall number of deaths that occur. In addition to this our data is probably skewed, since we have been attributing all deaths that have a positive PCR as Covid-19 deaths, regardless of whether the Covid-19 was the main contributory factor to the death or not.

I feel ‘we’ have been railroaded into the mentality of ‘test, test, test’ from an international perspective. The increased number of tests announced daily creates a sense of accomplishment and control of the disease. The Opposition has taken every opportunity it has to ram home this point of needing extra testing as well, without actually doing what a responsible Opposition should be doing: critically evaluating what is being done and providing constructive criticism.

Covid-19 is going to be with us for the foreseeable future. Now an antigen test is being introduced into the mix as well. How does this test compare with PCR testing? We need a rational plan based on scientific evidence as to what our testing protocol should be. This plan should be based on an economic model that can work for us. We should not be pressured into a process that has little scientific validity and more importantly something we as a country cannot afford.