It has been well over a year since the coronavirus pandemic was declared and many countries are now navigating through a third wave. Canada is no exception and this time with more cases than in waves past. Medical statistics demonstrate that the cases are more complicated among a younger portion of the population1. Considering that we are not completely sure how effective vaccines are, how long they will provide immunity, or if they are effective with variant strains, coupled with the fact that many economical activities must continue; testing more people, rapidly, becomes a greater necessity.
As governments and public health officials start to explore ways to open the economy safely, businesses and employers are also working on strategies to keep their employees and customers safe. We recently shared some things to consider when creating a covid testing strategy, you can read more about that here: Creating an Effective COVID-19 Testing Strategy.
In this blog we’ll compare two main testing strategies for COVID-19: diagnostic testing and screening testing and provide some information on how you can use portable PCR tests or antigen tests in a COVID-19 screening testing strategy.
What are the main strategies for COVID-19 testing: diagnostic vs screening?
Diagnostic testing, which often uses polymerase chain reaction (PCR) tests, can confirm if someone has COVID-19. Diagnostic testing often takes a few hours to days since these tests are typically performed at a central lab. This type of testing strategy is what is used by public health agencies and medical professionals to determine if someone who is experiencing symptoms is sick with COVID-19 (i.e. diagnose their illness).
In comparison, screening tests, which often use antigen tests, identify likely positive cases and provide results in a few minutes to an hour. These tests do not “diagnose” the patient on their own, as any positive results are considered preliminary and need to be confirmed by a diagnostic test. Screening employs tests that can be done quickly and can be performed anywhere (i.e., on-site, at the place of employment) by a health professional or trained individual and don’t need to be sent to a central lab. This kind of test is sometimes called a rapid point-of-care test (POCT). This fast turn around time is needed if you are screening people as they enter a workplace or event and is often done on people who do not have symptoms.
Can PCR Tests be “Rapid”?
PCR tests, although not as rapid as antigen tests, can still be very fast at providing on-site results. There are portable, small-scale solutions, such as the Biomeme SARS-CoV-2 test. This solution enables multiplex real-time detection of up to 9 samples to achieve sample-to-result in about 60 minutes (excluding sample prep time). When you break that down, 9 samples in about 60 minutes translates to about 7 minutes of processing time per sample. There is nothing slow about that turnaround time.
PCR vs. Antigen Tests for Screening
PCR tests look for genetic material from the SARS-CoV-2 virus that causes COVID-19. Once a sample is collected by a health care professional, these tests can be done quickly (results in 1-2 hours) on site or can be done in a large central lab (anywhere from a few hours to a few days to get results). These tests are the gold standard and can be used to diagnose a COVID-19 infection without any additional confirmatory tests. They often require specialized equipment to run the test (ex. a thermocycler) and with the right setup can be used in a remote setting.
Antigen tests are designed to detect pieces of the proteins that make up the virus. These tests are used to detect if a person is currently infected but tend to perform better if a person has had symptoms for a few days. Once a sample is collected by a health care provider, antigen tests can often be done quickly while you wait (a few minutes to about an hour or so). One thing to keep in mind is that for the current antigen tests on the market, an additional PCR test is required to confirm a positive antigen test result. Since antigen tests do not typically require a lot of special equipment, they can be well suited to remote settings.
Below are the major differences between antigen and PCR tests.
|Characteristic||Antigen Testing||PCR Testing|
|Detection||Detects proteins from the surface of the virus||Detects viral genetic material|
|Specimen Collection||Nasal or throat swab||Nasal or throat swab|
|Preparation||Sample added to a reagent||RNA is extracted using a chemical reaction process and specific dyes are added|
|Device||A sample is mixed in liquid is added to the detection module (cartridge)||A machine is used to amplify the genetic material of the virus that is potentially present in the sample|
|Results (what it tells you)||Whether the virus is present in high concentration (if you are likely to be infectious)||Whether any viral genetic material is present, even at low levels|
|Lab Skillsets||Can be performed by non-experts, non-medical professionals||Requires specialized equipment and laboratory skillsets|
|Time Delays||15-30 minutes||Hours or days|
|Costs||Not expensive||More expensive|
|General Reliability*||Can miss infection with low virus level||Very sensitive and specific|
*The chances that a test result is a true negative or a true positive depends not only on a test’s reliability but also on background rates of infection and on whether a person shows symptoms.
What are the Benefits of Antigen Testing?
Rapid antigen tests aim to identify or rule out COVID-19 infection in people with or without COVID-19 symptoms – this is dependent on the test and what it has been approved for by Health Canada. They are what most people think of when they think of a screening style testing strategy.
Generally, the benefits of antigen testing when used in a screening testing strategy are:
- They are portable and can be used wherever the people to be tested are (point-of-care)
- They are easy to perform, with a minimum amount of extra equipment, complicated preparation steps, or extensive training
- They are less expensive than standard laboratory tests or mobile PCR tests, allowing you to screen more people for the same budget amount
- They do not require a specialist operator or setting
- They provide results while you wait – typically within about 15 minutes and an experienced operator can run more then 1 test at once.
What are the Benefits of PCR Testing?
PCR tests are currently the most commonly used type of test to detect whether a person has an active COVID-19 infection. They are most often used by central labs as diagnostic tests, but certain portable PCR test platforms are ideally suited for screening strategies.
Generally, the benefits of portable PCR testing when used in a screening testing strategy:
- It is the “gold standard” test for diagnosing COVID-19 because it is the most reliable
- It is highly accurate, with high sensitivity and specificity rates
- Due to their sensitivity, they can detect asymptomatic samples much more easily
- Portable tests are small and lightweight, while lab based tests require large equipment.
- Relatively easy to perform; a sample is collected just the same way it is for an antigen test, and then it is prepped, with minimal steps to be processed.
- They often have software that makes it easy to understand and record the results
- Samples can be prepped and processed in about 2 hours, and typically more than one sample at a time. As an example with the Biomeme COVID-19 test, an experienced operator can prep and process 9 samples in 2 hours with just one Biomeme device.
Reliability of Antigen Tests and Portable PCR Tests
The question many people are asking about rapid tests is: “Are the commercially available rapid point-of-care antigen and PCR tests accurate enough to diagnose COVID-19 infection reliably?”
Scientists from the University of Birmingham in the UK recently published a systematic review study2 tackling this very question. In their publication, which summarized the results of 64 different studies, they investigated sixteen antigen tests and five commercially available rapid PCR tests, with rather interesting results.
In people with confirmed COVID-19, antigen tests correctly identified infection in an average of 72% of people with symptoms, compared to 58% of people without symptoms. Tests were most accurate when used in the first week after symptoms had developed (an average of 78% of confirmed cases had positive antigen tests). This is likely because people have the most virus in their system in the first days after they are infected. In people who did not have COVID-19, antigen tests correctly ruled out infection in 99.5% of people with symptoms and 98.9% of people without symptoms.
The study concluded that some of the assessed antigen tests are accurate enough to rival RT-PCR tests when used with people with symptoms. The author’s of this study concluded that antigen tests may be considered for quick decision making or when RT-PCR testing is unavailable, which is what makes them suitable for screening large numbers of people at a work site or event.
Rapid PCR Tests
Overall results for diagnosing and ruling out COVID-19 were good with rapid PCR tests, with 95.1% of infections correctly diagnosed and 99% correctly ruled out. In the same study, several point-of-care PCR tests show very high accuracy and potential for use. These point-of-care or portable PCR tests are a great option for setting up a screening program for COVID-19.
The graph illustrates the sensitivity difference between a low sensitivity antigen tests and high sensitivity PCR tests. PCR testing will detect the presence of the virus over a much longer time period, and not just at a time when the viral load is very high.
Source: Adapted from A. Crozier et al. Br. Med. J. 372, n208 (2021).
What is the Best Solution for Implementing a COVID-19 Screening Program?
Businesses that do not want to wait several hours or days to have accurate results to maintain their production may consider a rapid, portable PCR test. The Biomeme SARS-CoV-2 test is a real-time PCR test, approved by Health Canada, that delivers results in about 2 hours (including RNA extraction). This is relatively fast compared to national or provincial laboratories that return results in two or three days, or even with private laboratories that return results in 24 hours.
While antigen tests are not as sensitive as PCR tests, they provide a result in as little as 15 minutes and are often more cost-effective. However, given their lower sensitivity, a negative result on an antigen test should not be interpreted as though the individual does not have COVID-19.
Those receiving a positive antigen result should seek a PCR test as soon as possible for a confirmatory diagnosis. This also allows local public health authorities to identify the nature of the virus and track variants of concern.3
In conclusion, a complete solution to consider is coupling a rapid PCR test, such as the Biomeme SARS-CoV-2 test, with a reliable antigen rapid test in your screening strategy. This will ensure you have the most accurate rapid detection for point-of-care use. This combination is especially helpful in locations where the wait times for lab-based PCR test results is long. One combination strategy may be that a PCR test can be used for symptomatic and asymptomatic people who, due the nature of their job may have a hard time distancing, and the antigen test can be administered to a larger number of lower risk people. A PCR test can be used to confirm potential positives and liaise with local public health authorities for positive contact tracing.
To learn more about how the Biomeme SARS-CoV-2 test could fit into your COVID-19 screening strategy, please get in touch.
2 Dinnes, J. et al (2021). Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection. Cochrane Database of Systematic Reviews. https://doi.org/10.1002/14651858.CD013705.pub2