Information for Health Professionals
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 limited testing, as of March 2020, no country had reliable data on the prevalence of the coronavirus [COVID-19] in their population. As of 18 April, the countries that published their testing data have on average performed an amount of tests equal to only 1.1% of their population.
One of the key factors in tackling the spread of COVID-19 across the globe is testing.
In Australia, there are two main types of SARS-CoV-2 tests, these 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
The Therapeutic Goods Administrator [TGA] has approved 38 tests for inclusion on the Australian Register of Therapeutic Goods (ARTG) – as of 20th April 2020.
- 14 Nucleic Acid Test
- 24 Serology 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.
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 new 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
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 will likely take between 5-7 days 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 PoCT 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. In addition, the false-negative rate associated with these lateral flow devices is not known. False-negative results pose a significant risk to outbreak control and management.
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.
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 is imposing conditions of supply on serology-based COVID-19 tests for use at the point of care [POC]. The correct interpretation of test results in conjunction with the clinical presentation of a patient is critical to informing patient management and minimisation of further transmission of the virus. Accurate identification of a COVID-19 infection based on serology results, particularly those obtained from rapid tests used at the point of care, requires an understanding of the antibody response profile.
Testing for serious infectious diseases, such as COVID-19, need to be conducted in conjunction with a medical practitioner or other suitably qualified health care professional who can provide an individual with appropriate advice and treatment if required. The misinterpretation of serology results in the point-of-care setting if testing is not performed by suitably qualified persons with appropriate skills and knowledge presents grave risk to public health, which could result in serious illness and death of the patient and other persons that the patient comes into contact with.
Further clarification relating to the specific conditions is provided below:
- 1(a) accredited pathology laboratories (under the Health Insurance Act 1973) are those accredited as medical testing laboratories eligible for claiming to Medicare for approved pathology services.
- 1(b) this includes supply to a medical practitioner who may then oversee/guide the performance of testing by a registered/enrolled nurse.
- 1(c) allows for supply to a medical practitioner or registered/enrolled nurse in a residential or aged care facility.
- 1(d) and (e) the conditions also allow for supply of the Device to the Government for the purpose of the national stockpile. The Government maintains control of the stockpile and is responsible for ensuring that devices to test for COVID-19 that are included in the stockpile are provided to suitably qualified persons with appropriate skills and knowledge.
How Point of Care Testing Works
Western Australia – Prohibition on the use of Point of Care Serology Tests Directions
The purpose of these directions is to prohibit a person from using a point of care serological (blood) test (including an assay or device) (POC Test) as an acute illness diagnostic tool for COVID-19, as their use may adversely affect the prevention, control and abatement of the serious public health risk present by COVID-19.
4. Unless otherwise directed under the Act, a person must not use a POC Test as a tool to detect or diagnose COVID-19.
It is an offence for a person to fail, without reasonable excuse, to comply with any of these directions, punishable by a fine of up to $20,000 for individuals and $100,000 for bodies corporate.
FUN FACT – Back to words: let’s start with immunity
The word comes from the latin term “immunis”, meaning “without tax”. Roman soldiers who had returned from foreign wars could, at least for a time, be granted tax-exempt status as members of the Genio Immunium, which owed adherence to the Goddess Minerva. Minerva had a number of divine portfolios, including wisdom, medicine, the arts and defensive warfare. The “tax” that immunity has evolved to defeat is the tax of infection.