COVID-19 Tests and risk mitigation in the workplace.
One of the most prominent issues since the beginning of the COVID-19 pandemic involves the ability to test populations for virus detection. This is an essential element in the fight against COVID-19 and our ability to curb its spread. However, polymerase chain reaction (PCR) testing is not a panacea and may even create an illusion of security if it is not used judiciously.
How does a PCR test work?
The PCR test, invented in the 1980s, was designed to study the genome of all living forms and has paved the way for many medical and environmental applications. The identification of viruses is one such application, highlighting its role within this pandemic.
If you have suspicious symptoms for COVID-19 and get tested, a technician will take a sample of the secretions from your nasal mucous membranes and the back of your throat with a miniature cotton swab. This measure is designed to extract some of the virus from its likely locations. If the virus is present in the swab, the PCR test device (called a thermal cycler) will detect the presence of the virus in as little as one millilitre of secretions or saliva with a high level of accuracy.
The device searches for an RNA fragment that is unique to the COVID-19 virus. Each time it finds the sequence, it makes a copy and adds fluorescent dye. As the copies are made, when the level of dye reaches a certain amount, the software issues a positive report. This report must be interpreted by a trained technician to confirm the presence of the virus.
Is the PCR a perfect solution?
Unfortunately, the PCR test is not the best solution to thwart COVID-19. Firstly, the test is reliable only if the virus is present in sufficient quantity in the sample. Therefore, it is necessary to collect the sample at the right place, with the right technique, and at the right time during the evolution of the infection.
Method and location: Several sampling methods are currently approved, most frequently the swab technique at the back of the throat and nose. Swabbing from the anterior portion of both nostrils is less traumatic but may be less reliable. Finally, more scientific data has showed that saliva would be an equally good vector to detect the presence of the virus.
Timing: Since the goal is to detect the presence of the virus, it is important to understand the progression of the virus from first contact to infection. This is called the incubation period and is followed by the infectious period, which varies greatly from person to person depending on the level of severity. Lastly, patients enter the recovery period. The incubation period can vary widely (up to 14 days), but it is 5-7 days in the vast majority of cases. The contagious period, when the virus can be detected, begins about 3-4 days before the infection occurs when the virus is present in larger amounts, and it persists for 7-10 days after the infection begins and once the symptoms have resolved. Note that traces of the virus can persist for many weeks even after recovery from the infection.
Considering all these factors, we end up with the following conclusion: the PCR is an excellent test to detect the presence of a virus but can "miss" it in up to 30% of cases if the timing or technique does not allow the technician to sample enough of the virus. In asymptomatic individuals, the test is less reliable than in symptomatic individuals, and even symptomatic individuals may receive false negatives (i.e., an infected individual with a negative test).
Does this explanation suggest that screening tests are useless? Not at all! In fact, they can be quite useful as part of a comprehensive risk-control strategy for a group of workers or a select population. For example, Iceland has quickly controlled the transmission of the virus by testing the majority of its population and quickly isolating positive individuals who did not know they were carriers and contagious.
However, at the individual level, we must be careful of relying only on the test result when making decisions. Trusting PCR results alone may encourage us to lower our guard with regard to following clearly established preventive measures (e.g., physical distancing, wearing a mask, and washing our hands). To complement PCR results, the expertise of infectious disease consultants is vital to establish a risk control strategy that addresses each situation and each group of individuals.
What other methods can detect COVID-19?
Currently, two other tests can help determine whether an infection is active or old.
The antibody test, as the name implies, looks for the presence of antibodies specific to the COVID-19 virus that the body produces in response to the presence of the virus. Therefore, this test can be useful in demonstrating whether an individual has ever been in contact with the virus. However, it cannot tell which phase of the infection they have entered. Also, despite what some interpretive statistics may suggest, only a small percentage of the population has been exposed so far in areas that have strict public containment and hygiene measures in place, making the usefulness of this test less important at this time.
Finally, the latest addition is the antigen test, which attempts to identify the virus by means of its physical characteristics, searching for virus-specific proteins. Thus, this test allows the identification of the virus when it is active and could prove to be an interesting addition to the arsenal of virus screening for some groups. Since it is much less expensive, can be done daily, and requires no tools and only a little saliva, it would allow health experts to identify in a few minutes the presence of the virus, which could then be confirmed by a PCR test. At the moment, few of these tests are approved, and their reliability has not yet been demonstrated. They will likely become popular in the coming months, especially for monitoring groups of workers or stable populations.
The conclusion is quite simple: there is no quick fix or lack of risk during a pandemic. The various tests available on the market should never be applied as a single risk management measure. Instead, they should function as part of a global solution and include the following elements:
To obtain the most up-to-date information, it is important to work with organizations that are well versed in all the elements of risk management.
Marc Gosselin MD
Medical Director SIRIUSMEDx / Whitecap RSC