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COVID-19 testing in Australia - information for health professionals
Tests for COVID-19 aim to detect the causative virus, SARS-CoV-2, or an immune response to SARS-CoV-2.
The reliability of COVID-19 tests is uncertain due to the limited evidence base. Available evidence mainly comes from symptomatic patients, and their clinical role in detecting asymptomatic carriers is unclear.
The two main types of SARS-CoV-2 tests are:
- Nucleic acid detection tests - using qPCR to detect SARS-CoV-2 viral (Ribonucleic acid) RNA; and
- Serology tests - to detect IgM and/or IgG antibodies against SARS-CoV-2
Nucleic acid/PCR tests
Reverse transcriptase Polymerase Chain Reaction (PCR) tests detect SARS-CoV-2 nucleic acid (RNA). Most of these assays typically take several hours (including specimen processing time) to generate results, and require complex laboratory equipment and trained technicians. There are now some near patient SARS-CoV-2 PCR instruments available that can be used outside of a laboratory. These systems can provide quicker results, but cannot do as many tests at once.
PCR tests are currently considered to be more clinically sensitive than serology assays for detecting early infections and, because they directly detect viral RNA, they are an indicator for viral shedding. The extent to which a positive PCR result correlates with the infectious state of an individual is still being determined. Clinical resolution and consecutive negative PCR tests in a previously positive individual are currently being used as criteria when considering release from isolation. However, this may change with increasing knowledge around SARS-CoV-2.
Serology antibody tests
The TGA has received and undertaken an expedited assessment of a number of applications for point-of-care (often referred to as PoC or PoCT) serology tests that utilise lateral flow immunoassay technology.
Point-of-care serology tests are intended to detect IgG and/or IgM antibodies to SARS-CoV-2 from venous or finger prick blood samples that are placed on a test strip. These tests look similar to common pregnancy tests. Results take about 15–30 minutes.
There is a window period between virus infection and the production of IgM and IgG antibodies, and the sensitivity and specificity of IgM/IgG antibody tests early in SARS-CoV-2 infection is not well characterised. Antibodies can take up to two weeks or more to become detectable after infection with SARS-CoV-2. Because antibody tests do not detect active viral shedding, they cannot detect if an individual is infectious. Though they provide some useful information when combined with the clinical picture, a suggestive clinical picture plus a positive point-of-care may be considered sufficient for a presumptive positive diagnosis and subsequent management.
Human coronaviruses circulate frequently every year and cause a common cold type illness. Cross reaction with antibodies formed by current and past exposure to seasonal human coronavirus infections can cause false-positive results. Serology tests can also fail to detect COVID-19 if testing is performed in the acute phase of the infection prior to the development of detectable antibodies.
Serology antibody assays generally provide historic information about viral exposure. They can indicate whether an individual has past exposure to SARS-CoV-2. It is not yet evident that the detection of antibodies in lateral flow devices reflects the presence of protective immunity, so the detection of antibodies may not exclude remaining infectivity in a patient.
COVID-19 test performance
COVID-19 is an emerging viral infectious disease. There is limited evidence available to assess the accuracy and clinical utility of available COVID-19 tests.
Due to the urgent nature of the COVID-19 pandemic, a number of SARS-CoV-2 tests have undergone an expedited assessment by the TGA to enable their legal supply in Australia. These expedited assessments are based on the limited clinical and performance data currently available. All SARS-CoV-2 tests currently approved for supply are required to provide updated evidence to support the ongoing safety and performance of the tests to the TGA.
The TGA is conducting a post-market review of all approved COVID-19 point-of-care serology tests to verify their performance and inform their best use. The Department of Health has engaged the Peter Doherty Institute to assist in the post-market validation of these tests.
There is also an exemption Therapeutic Goods (Medical Devices—Accredited Pathology Laboratories) (COVID-19 Emergency) Exemption 2020 in place which allows the supply of unapproved SARS-CoV-2 tests (those that have not yet undergone expedited TGA assessment) to accredited pathology laboratories. Unapproved point of care tests can also be supplied under this exemption, but only to an accredited laboratory.
Note: In Australia, the supply of self-tests for most serious infectious diseases, including self-tests for COVID-19, is prohibited under the Therapeutic Goods (Excluded Purposes) Specification 2010.
The TGA will take action in relation to any report of poor or faulty performance of these devices. Reports can be submitted via the TGA website.