LETTER: The value of testing in the fight against Covid-19
Extensive testing is vital not only to study the current coronavirus outbreak, but also to plan for future pandemics
In the absence of testing we don’t know what we don’t know. It’s like flying an aeroplane with 500 passengers on board, without a flight navigator or GPS co-ordinates, in the dark, in poor weather conditions and an unknown mountainous territory. That’s a disaster. The worst thing in medicine is the unknown.
A PCR test (the nasopharyngeal swab) identifies people who are actively infected. In other words it helps us know who is infectious. The PCR detects the actual genetic identity of the virus. The caveat is that it has a 15% false negative rate. In the context of the scale of the disease this does not negate the usefulness of the test.
So, PCR gives an indication of where you are now. In other words, the flight GPS co-ordinates. This aids public health interventions such as contact tracing, quarantine and isolation. In addition, without this test, the reproductive rate which determines the community transmission of the virus remains an illusion.
The reproductive rate is important for interventions and planning. The determined reproductive rate (R0) of the novel coronavirus is between two and three. This means that each infected person will infect at least two to three other people. This is highly contagious compared with previous coronavirus strains.
This means that social distancing helps reduce this rate but does not eradicate the virus. An isolated person or a person on quarantine if done properly will not infect anyone until recovery. If all people who are infected do not infect another person then the virus spread will be stopped completely. The ideal reproductive rate for return to normal is an R0 of one or less. In this circumstance each infected person can at least infect only one other person. Both the spread and the management of the illness in this instance is under control.
The serological antibody tests under clinical trials will give us an indication of everyone who has been previously exposed to the virus. This means that even if a person never tested for Covid-19 or never got sick from Covid-19 we can tell if they were once infected in a retrospective manner. Why is this important? It is important because it will give an indication of the level of herd immunity in the population. Depending on the type of virus, herd immunity is only acquired once a certain proportion of the population, at least above 70%, has been exposed and recovered from an infection.
The caveat to this type of test is that the serological antibody detection may erroneously pick up other previous coronaviruses that a person has been exposed to without discriminating between them and the current new coronavirus. This may result in false positives and therefore an inaccurate interpretation of the situation. However, studies are ongoing to fine-tune these tests. Recently a Roche antibody test has been reported to have a specificity of 98.8% and sensitivity of 100%.
The other unknown is that it has not been shown whether exposure to the virus leads to clinically significant natural immunity and if it does, how long does this immunity lasts. Nevertheless, knowing the extent of exposure is a good start. The clinical trials to settle this matter need our support. The antibody tests will give a trail of where you have been. It’s the genetic print of the virus. The flight black box that is crucial following the aftermath of the pandemic. It will help study the current pandemic further and plan for future pandemics.
Lastly, in dealing with a highly contagious public health problem it is imperative to have a geographic map distribution of the disease. This helps to plan intervention measures, plan distribution of resources, impacts on policy formulation and aids epidemiological analysis of the pandemic. Furthermore, the data from testing, both PCR and serological antibody tests, will aid the planning and distribution of the vaccine once it becomes available.
Therefore, everyone ideally should have either a PCR test or a serological test at some later future date. Without testing you simply don’t know how many people are infected, what is the distribution of the spread, in other words the map of the outbreak, and the reproductive rate cannot be determined.
In view of the shortage of resources in terms of testing kits, facilities and personnel, such testing can then be temporarily rationed to target specific hot spots and high-risk populations, or to dictate decision-making regarding reopening. Thus, the value of testing is important as a baseline and a surveillance tool.
The basic principles to a pandemic remain testing, contact tracing and isolation.
Dr Lehlohonolo Dongo
JOIN THE DISCUSSION: Send us an e-mail with your comments. Letters of more than 300 words will be edited for length. Send your letter by e-mail to firstname.lastname@example.org. Anonymous correspondence will not be published. Writers should include a daytime telephone number.