Les tests salivaires de détection de l’infection active au coronavirus 2 du syndrome respiratoire aigu sévère

(Contenu en anglais seulement)

New saliva-based tests for severe acute respiratory syndrome coronavirus 2 are more comfortable for individuals being tested and may pose less risk to health care workers than alternative tests

Nasopharyngeal, deep nasal, and throat swabs are commonly used to collect the sample needed for testing to detect diseases of the upper respiratory tract like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).^1-3 However, widespread testing using traditional nasopharyngeal swabs has proven to be challenging given shortages of critical testing supplies such as swabs and reagents, as well as shortages of personal protective equipment for the health care practitioners who perform the tests.^4,5 In addition to these shortages, nasopharyngeal, deep nasal, and throat swabs are difficult to perform and can be quite uncomfortable for the individual undergoing testing.⁶

Saliva-based tests for SARS-CoV-2 are an emerging alternative to traditional testing. These tests require different supplies than the standard swabs, which could help ease medical supply shortages. Additionally, some saliva tests can be self-collected, so they may result in less risk of exposure to the SARS-CoV-2 pathogen for health care workers. They are also easier to obtain and less invasive than standard nasopharyngeal, deep nasal, and throat swabs. If proven to be effective and accurate, these tests could be a component of the robust testing strategy necessary for controlling the COVID-19 pandemic.

How It Works

There are two saliva- or oral fluid–based tests that have received Emergency Use Authorization (EUA) from the FDA to diagnose active SARS-CoV-2 infection: the Rutgers Clinical Genomics Laboratory TaqPath SARS-CoV-2 Assay (the Rutgers test) and the Curative-Korva SARS-CoV-2 Assay (the Curative-Korva test).^7,8 They are both molecular reverse transcriptase polymerase chain reaction tests that detect the virus’s genetic material in a specimen provided by an individual deemed by their health care provider to be at risk for COVID-19.^7,8

The first saliva test to receive EUA by the FDA was the Rutgers test.⁷ This test can be used to detect SARS-CoV-2 in multiple sample types, including a saliva sample. The assay is designed as a diagnostic test to detect ribonucleic acid from SARS-CoV-2 in respiratory droplets from patients with suspected COVID-19.⁷ For saliva sample testing, the sample must be collected using the Spectrum Solutions LLC SDNA-1000 Saliva Collection Device.⁷ Under an update to the original EUA, the saliva specimen can be self-collected.⁹ To collect the sample, the individual spits directly into the collection device. The sample is then stored and transported to the Rutgers clinical genomics laboratory for testing.⁷ Testing of the specimen must take place within 48 hours of collection.⁷

The Curative-Korva test also received EUA by the FDA.8 The test can be used to detect SARS-CoV-2 in respiratory specimens from a variety of sample types, including oral fluid specimens.⁸ Unlike the Rutgers test, the Curative-Korva test requires the oral fluid specimens to be collected using a swab. In general, the collection of samples for swab-based oral fluid tests usually involves having an individual cough several times before swabbing the inside of both cheeks for several seconds.¹⁰ Although the specimens can be self-collected according to the EUA, the specimens must be collected under the supervision of a trained health care worker.⁸ The swab containing the specimen is then sealed in a tube for transportation to KorvaLabs where it can be tested.

Who Might Benefit?

The benefits of these types of tests vary depending on how they are deployed. As samples can be self-collected, the tests do not require the same degree of direct contact between a health care worker and an individual suspected of having COVID-19 that a traditional nasopharyngeal swab requires. This is a potential benefit to health care workers as they would have less risk of exposure to the SARS-CoV-2 pathogen.¹¹

Another group that might benefit from these new saliva-based tests would be individuals who are symptomatic for COVID-19 and require testing for a diagnosis. Increased availability of tests could result in increased testing capacity, which may lead to shorter waiting times for testing. Furthermore, providing a saliva sample is more comfortable and less invasive than a nasopharyngeal swab, which might decrease the stress experienced by an individual being tested for the pathogen that causes COVID-19.^12,13

Finally, if these new saliva-based tests are proven to be accurate, the additional tests could contribute to an increased capacity for widespread testing. The ability to test large groups of people with or without COVID-19 symptoms is a necessary part of a public health strategy to manage the pandemic.¹⁴

Availability in Canada

At the time of this report, neither the Rutgers test or the Curative-Korva test are authorized for use in Canada as a testing device for use against COVID-19,¹⁵ nor does either test appear on the list of applications received by Health Canada for diagnostic devices for use against COVID-19.¹⁶

What Does It Cost?

The Rutgers test is available in New Jersey at a cost between US$65 and US$100 per test.¹⁷ No cost information about the Curative-Korva test was found.

The availability of multiple types of diagnostic tests for SARS-CoV-2 might help to reduce costs for the health care system as multiple tests could reduce shortages of testing supplies, which may prevent surge pricing. Additionally, tests that allow for self-collection could contribute to reduced costs as some do not require the presence of a trained health care worker for specimen collection.^2,3

Current Practice

In Canada, diagnostic testing for SARS-CoV-2 has been done by the National Microbiology Laboratory in close collaboration with provincial and territorial public health laboratories.¹⁹ Criteria for testing varies by jurisdiction and has changed over time. While nasopharyngeal swabs are often used for diagnosing active SARS-CoV-2 infection, testing may be performed in a variety of ways and could be based on several specimen types such as nasopharyngeal swab, deep nasal swab, throat swab, or sputum sample.^2,3

What Is the Evidence?

Testing for an Individual Diagnosis

Saliva samples can be used to detect diseases of the upper respiratory tract and scientists have theorized that saliva-based tests might be useful for detecting SARS-CoV-2.^6,11,20-25 There are some published studies that report on the detection of the SARS-CoV-2 pathogen in saliva and oral fluids;^13,26-28 however, due to the novelty of the pathogen, the body of research is limited, and study populations are very small. It should be noted that while SARS-CoV-2 can be detected in saliva, there is evidence that suggests that different specimen types from the same individual can yield conflicting results.^13,26,29 In addition to these studies, there are several ongoing clinical trials to evaluate tests that use saliva to detect SARS-CoV-2.^30-34 

Due to the nature of the COVID-19 pandemic, there is a push to make research about the topic accessible. In some cases, publishers have made information about COVID-19 accessible by not putting this research behind a paywall. Another way research results are more accessible during the pandemic is by posting online before peer review. While posting before peer review can speed up the time frame for access to emerging COVID-19 research, it may also have the effect of compromising the quality of the research. There are several preliminary reports on testing saliva for SARS-CoV-2 infection that have not yet been peer reviewed.^35-38 The early results of these non-peer reviewed studies support the use of saliva-based testing to detect SARS-CoV-2; however, it is important to note that many of these studies report that different types of tests had conflicting results. The same individual might test both positive and negative for SARS-CoV-2 based on different specimen types, and none of the sample types was able to detect all instances of SARS-CoV-2.^36,37

Screening of the General Population

There is no universally agreed upon gold standard or reference test for diagnosing the SARS-CoV-2 pathogen because it is so new.^39,40 It is difficult to establish the diagnostic accuracy of any new test without a reference standard test. While information about diagnostic accuracy and disease prevalence are linked, when the prevalence of a disease is low, even small imperfections in test accuracy lead to substantial numbers of misdiagnoses.¹⁴ In order to discover the prevalence of COVID-19 cases in a population, it is necessary to test a random sample of both symptomatic and asymptomatic people.¹⁴ Critically, the saliva tests that are available are expressly meant to be used to test individuals who are symptomatic.^7,8 More data is needed to establish a reference test or gold standard for the diagnosis of COVID-19, saliva-based or otherwise, in order to establish prevalence of COVID-19 in the population. One protocol was identified that proposes to validate home specimen collection methods for SARS-CoV-2.⁵ This research is intended to contribute to the evidence base to guide public health responses to the COVID-19 pandemic.⁵

Issues to Consider

Scalability

The saliva-based tests that have received FDA EUA are proprietary, and all specimens collected for each test must be processed by the lab that created the assay. This could make scaling up difficult as the number of tests would be limited by how many tests an individual lab can process each day.^7,8

Comparing Test Results

There is emerging evidence that different types of samples collected may yield different results in the same individual being tested.^13,29 This finding makes it difficult to directly compare test results of different tests.¹⁴

When to Test

There is evidence emerging that viral loads of SARS-CoV-2 in saliva are highest during the initial phase of infection (the first week) and decline over time.²⁸ This is consistent with other data that suggests pharyngeal virus shedding is highest in the first week of symptoms.⁴¹ It is therefore likely important to use these types of tests in the initial stage of infection.

Related Developments

In addition to the previously mentioned saliva-based tests, there are at-home tests for COVID-19 emerging. The nasal swab test created by Laboratory Corporation of America (LabCorp) is an at-home nasal swab test that can be self-administered.⁴² The Pixel test was the first at-home test granted EUA by the FDA.⁴² The Pixel is a reverse transcriptase polymerase chain reaction test that detects genetic material from the SARS-CoV-2 virus in upper and lower respiratory specimens.⁴² As the Pixel test can be used with a home specimen collection method, this test does not need to be performed in the presence of a health care worker. Like the Rutgers test and the Curative-Korva test, the Pixel test is designed to diagnose an individual whose health care provider suspects they have contracted COVID-19.⁴² The test is performed by collecting a nasal swab from just inside both nostrils.⁴³ After the specimen has been collected, the swab is placed in a collection tube and stored in a biohazard specimen bag for transportation to LabCorp for testing.⁴³ The testing kits by LabCorp cost US$119.¹⁸

Looking Ahead

There is information emerging that shows that saliva tests may be useful for making an individual COVID-19 diagnosis. Saliva-based tests may result in safer and more comfortable testing for health care workers and those being tested. However, more research is needed about the diagnostic accuracy of these tests in order for them to be deployed for widespread testing of the population.

Author: Sarah Jones

References

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