Our world has changed dramatically since March 11, 2020, when the World Health Organization (WHO) declared that COVID-19 would be characterized as a pandemic[1]. The significance of this and the longevity of the measures we need to follow to prevent massive spread is just starting to become a reality for many.

Employers, however, have been faced with the realities of the impact of the pandemic since early 2020 with many spending countless hours determining the best way to protect their employees, the public, and their business model. How do you continue to keep your workforce at work? How do you prevent an outbreak? How do you deal with an outbreak? What changes are required in order to meet the requirements of Public Health standards? These are only some of the questions that employers across Canada have had to deal with to ensure the health and safety of their workers during this unprecedented pandemic.

We have been told by many sources that testing for COVID-19[2] [3], to capture those who are pre-symptomatic (the few days prior to presenting with symptoms but where the individual is shedding virus and can spread the disease) and asymptomatic (those who have the virus, are shedding it, spreading to others but have no discernible symptoms) is one of the key strategies to prevent spread. This has led many workplaces in Canada to inquire about screening and testing their employees.  

Testing can play an essential role in a return-to-work strategy, but there are many considerations to take into account, such as procurement, logistics, data privacy, and communications. The decision to conduct private testing in the workplace also needs to take into consideration current private laboratory capacity for handling and processing test samples. Current public health directives have required private labs to process public samples first, and to be available for surge capacity if required, and only process private tests if there is residual lab capacity. Private samples cannot take precedence over public health samples and may be further regulated by provincial public health units as necessary. This article is not intended to provide advice regarding whether or not to begin testing in your workplace, but rather to provide guidance as to what tests are currently available and being used in Canada. Having this knowledge helps to not only understand what tests may be beneficial in the workplace but to understand and interpret the results of a test that an employee may have had, whether at work or through Public Health testing.

This is a very dynamic topic with an exponential growth of knowledge from day to day.  Health Canada continues to approve testing devices on an ongoing basis with considerable development of new testing technologies across the world. The information provided in this article is based on the information that is available today and is likely to change quickly. For any questions or for the most up to date information, feel free to reach out to DriverCheck Inc.  

In Canada, there are presently three different types of tests for COVID-19 that are authorized by Health Canada.

1. Nucleic Acid Testing (Reverse transcription-polymerase chain reaction, RT-PCR)

2. Serology Testing (Antibody testing)

3. Antigen Testing

Health Canada also indicates whether these tests can be used in the laboratory (lab-based) or are authorized as point-of-care-testing (POC) which can be used in a location outside of the laboratory.

As of October 15, 2020, there are 41 different COVID-19 testing devices authorized by Health Canada. Of these, 28 are nucleic acid tests, 11 are serology tests and two are antigen tests. The antigen tests are all authorized for use as POC, the serology tests are authorized only for lab testing and three of the nucleic acid tests are authorized to be used as POC.

This leaves workplaces with only a few options for testing that can occur on site if they choose to do testing. At the moment, we are also limited by the availability of these tests as many have been earmarked by the government with few remaining for immediate use by employers or other organizations across Canada.  

Specimen Types

The accuracy of any test is in part based on the ability for the specimen to collect enough viral particles to be detected in the test being conducted. At this time, nasopharyngeal (NP) swabs are the preferred method to be used with studies showing the highest sensitivity in comparison to other swabs[4]. NP swabs do have some drawbacks including the ability to secure enough NP swabs, as well as the unpleasantness of the collection. When one test is being conducted with long timeframes between testing, the discomfort that is often associated with this type of collection can be well tolerated. However, for individuals who are part of a frequent testing protocol (every 2-3 days or even weekly), the preference has generally been for other specimen types that are considered more tolerable.

Anterior nares, mid-turbinate/deep nasal, and oropharyngeal tests are other commonly used specimen collections however they are thought to have a slightly reduced ability to collect viral particles thereby leading to a lower sensitivity for all types of testing. Testing of both nares and combining different locations of testing helps to increase the sensitivity.

Oral fluid swabs, saliva testing and “swish and gargle” testing are newer tests being used for collection in some locations. However, most of the test devices authorized by Health Canada have not yet been validated for these types of tests. It is likely that we will see more studies and support for this type of testing as the frequency and availability of testing increases across Canada.

Testing Devices

Before reviewing the details of each type of test, it is important to fully appreciate the timeline of the COVID-19 disease as outlined in Figure 1. Once exposed to the virus, it takes, on average, two days for the virus to replicate in the body to produce enough active virus to be able to spread to others. This timeframe is referred to as the latency phase. On average, there are then two days where an individual may feel well, however is able to shed virus and spread this to others. An individual may then become symptomatic, with symptoms ranging from mild to severe symptoms. On average, an individual becomes symptomatic on day five[5]. The SARS-CoV-2 virus is known to spread through respiratory droplets or small particles produced when an infected individual coughs, sneezes, sings, shouts, speaks and breathes.  These particles can then be inhaled into the nose, mouth, airways and lungs of an individual in close proximity, especially when there are no face coverings or masks being worn. There is some evidence that these particles can remain in the air and be breathed in by others, especially in indoor environments with poor ventilation[6] [7].  

Figure 1

Nucleic Acid Test (RT-PCR)

Nucleic acid tests are considered the gold standard test for detecting the presence of SARS-CoV-2. In Canada, this requires a swab, either NP sample, other nasal or oropharyngeal swabs (or combination of swabs). The ability to test using oral swabs or oral fluid is beginning to be validated and will likely become more commonplace in testing as discussed above, especially in circumstances where individuals require multiple tests over a period of time.

The sample is then sent to a laboratory or tested on site with one of the three available POC nucleic acid tests that are Health Canada approved. The virus’s RNA (if present) is extracted from the sample and converted into DNA. The DNA is then amplified, resulting in replications of the viral DNA in order to produce a result. If the viral load is high, there will not be the need for too many cycles of amplification to detect the viral genetic material above a set threshold. However, when the viral load is very low, there will be the requirement of many cycles of amplification in order to produce a detectable level.

While nucleic acid testing is very accurate, there are many reasons why we still continue to see false negative tests (a test that is reported as negative despite the individual having the virus). Some of the factors that play a role are:

1. Specimen collection – with poor collection technique, viral particles may not be collected with enough volume to result in a positive test

2. Type of specimen collected – as discussed above, NP swabs are the preferred collection due to their ability to best collect viral particles for testing. Other swabs have been validated and can be used for testing in Canada (anterior nares, mid-turbinate, oropharyngeal, etc) however there may be some degree of loss of sensitivity with these types of swabs as outlined above.

3. Nucleic acid tests are most accurate when the individual is symptomatic and has had symptoms for two to seven days. If the test is completed too early in the course of the disease, there may not be enough viral load to be detected resulting in a negative test despite having the virus.

The accuracy of lab-based nucleic acid testing and POC nucleic acid tests have been shown to be very similar regarding sensitivity, specificity and accuracy.  

Serological Testing

Serology testing is the test for specific antibodies that are produced in response to exposure to SARS-CoV-2. It takes at least 14 days for individuals to produce these antibodies and as such, they are not used to diagnose COVID-19. The presence of the antibodies does not exclude the risk of spread of the virus. In other words, it is possible to have both active virus and the early production of the antibodies.

There was some early thought that the presence of these antibodies would ensure that an individual is protected against further infection with the virus. At this time, we are aware of five confirmed instances of reinfection of the SARS-CoV-2 virus worldwide. With over 38 million individuals across the world having been diagnosed with COVID-19[8], this is a small number however it does emphasize the fact that antibodies may not protect against all strains of the virus and that the length of time of protection is still unknown.

The utility of serology testing for the workplace is very limited and not recommended at this time.

Antigen Testing

Antigen testing is the new kid on the block for Canada. Health Canada approved two devices in early October 2020. Antigen tests detect the presence of specific proteins found on the surface of the SARS-CoV-2 virus. A positive antigen test is highly specific meaning that if there is a positive test, the likelihood of it being a true positive is very high.

Although antigen testing has a specificity similar to nucleic acid testing and can be used for diagnosis of the virus similar to nucleic acid testing, they are not as sensitive especially during the latter part of the COVID-19 disease course. The sensitivity is highest during the pre-symptomatic phase as well as for the first few days of symptoms. After this time, the sensitivity and ability to detect the virus decreases.

The antigen tests that are currently approved by Health Canada can be used on site as POC tests. They are inexpensive in comparison to nucleic acid testing (both lab-based and POC tests) with results available within 15 to 30 minutes. The preparation time is short, and this does not require a lab technician or technologist to prepare the samples. Currently, the tests require either NP or nasal or oropharyngeal swabs (which do require a trained collector). At the moment, these have not been validated for oral fluid swabs or saliva testing.

In the workplace as well as in the community, the sensitivity and accuracy both increase with repeated tests. In an individual who has symptoms consistent with COVID-19 and a known exposure, a positive antigen test can be diagnostic. However, if the pre-test probability (the likelihood of the individual testing positive predicted prior to the test) is very low, with no known exposures, low community spread and no symptoms, a positive test should be repeated. The chance of two false positive tests in a row is not likely and therefore if the test is positive again, the likelihood of the individual being pre-symptomatic or asymptomatic is higher.

When used in the workplace as a quick, inexpensive screen, the recommendation is to conduct testing every 2-3 days (e.g. Monday, Wednesday and Friday OR Monday and Thursday). Nash et al (2020)[9] examined the impact of high frequency testing using less sensitive antigen tests. They reviewed public data from Brazil and the United States and concluded that when antigen testing (or testing with lower sensitivity in comparison to RT-PCR testing) is conducted twice to three times per week, there is a reduction in the spread of the SARS-CoV-2 virus, the rate of hospitalizations as well as deaths.

Using antigen testing in this manner increases the sensitivity when considering the testing regime as a whole. It also allows for quick detection of those who were recently exposed but may not yet been displaying symptoms of the virus.

Timeframes and Use of Different Tests

Figure 2 reviews the best timing for each test discussed above (based on the average course of the COVID-19 disease). The use of serology testing would be recommended only after 14 days since exposures (with the best sensitivities found between 14 and 21 days), however it is important to note that serological testing is not, at this time, recommended for use as part of a workplace strategy.

Figure 2

Summary

COVID-19 testing should be seen as an additional measure to add to the many strategies that workplaces have put into place to help reduce the spread of the virus in the workplace. If conducting workplace COVID-19 testing, it is important to note that positive tests do need to be reported to the local Public Health authorities and contact tracing should follow.

The addition of testing has been shown to reduce the transmission of SARS-CoV-2[10] [11] however workplaces need to consider all factors when deciding whether or not to implement COVID-19 testing. At the moment, even when deciding to conduct private COVID-19 testing in the workplace, there are limitations to the availability of the POC tests including POC nucleic acid tests as well as antigen testing. As Health Canada continues to approve new testing devices, there will likely be an increase in both availability and options for on-site testing.  

Employers need to be aware of many factors including the rate of community spread in their area, the limitations of all testing and the information regarding sensitivity and specificity of each test in order to be interpret what a test result really means. There are supports available for workplaces who are considering instituting testing and experts who can review protocols, and interpret test results. For more information, please do not hesitate to contact DriverCheck Inc.

[1] https://www.who.int/emergencies/diseases/novel-coronavirus-2019/events-as-they-happen

[2] https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/symptoms/testing.html

[3] https://www.nia.nih.gov/news/why-covid-19-testing-key-getting-back-normal

[4] https://www.idsociety.org/globalassets/idsa/practice-guidelines/covid-19/diagnostics/table-3.png

[5] https://doi.org/10.7326/M20-0504

[6] Morawska, L., & Cao, J. (2020). Airborne transmission of SARS-CoV-2: The world should face the reality. Environment international, 139, 105730. https://doi.org/10.1016/j.envint.2020.105730

[7] https://www.cdc.gov/coronavirus/2019-ncov/faq.html#Spread

[8] https://coronavirus.jhu.edu/map.html

[9] https://www.medrxiv.org/content/10.1101/2020.09.01.20184713v3

[10] https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30630-7/fulltext 

[11] https://www.medrxiv.org/content/10.1101/2020.04.30.20087015v4.full.pdf

DR. MELISSA SNIDER-ADLER, M.D., C.C.F.P.(AM), M.R.O. (AAMRO), D,A.B.A.M.

CHIEF MEDICAL REVIEW OFFICER, DRIVERCHECK INC.

PHYSICIAN, ADDICTION MEDICINE

Dr. Snider-Adler is the Chief Medical Review Officer for DriverCheck and is a Board-Certified Addiction Medicine Physician with a Certificate of Added Competence in Addiction Medicine.

Dr. Snider-Adler currently practices addiction medicine in Oshawa, Ontario and is an Assistant Professor at Queen's University Department of Family Medicine. She works as a Peer Assessor for the College of Physicians and Surgeons of Ontario.

Dr. Snider-Adler is considered an expert in the field of substance use in the workplace as well alcohol and drug testing for safety sensitive workplaces. As such, she is often asked to provide expert opinions, reports and testimony for arbitrations, hearings and court cases across Canada.

Dr. Snider-Adler travels across Canada and the U.S. speaking to workplaces and at various conferences regarding the impact of recreational cannabis, cannabis for medical purposes, workplace substance use, and addiction prevention and treatment.