The importance of testing for Coronavirus (COVID-19) has been highlighted as the key to easing lockdown measures, protecting people, the health services and the answer to re-opening the economy by means of controlling the infection rate.
However developing adequate tests for the detection of a novel virus is challenging. There are two important factors which need to be kept in mind when designing tests for COVID-19 (or any other diagnostic tests):
• Sensitivity (true positive rate) – Do we find what we are looking for in a sample every time? Even when there is a low concentration in a sample (which seems to be the case with COVID-19). How often do we detect people with COVID-19, having COVID-19.
• Specificity (true negative rate) – How many times do we find something specific we are looking for in a sample? This should be as close to 100% as possible. Do we correctly identify those without COVID-19 as without COVID-19.The UK had previously bought 3.5 million inadequate tests (£20 million worth from China) which had a low specificity (25%) so they could not be used to determine the specific COVID-19, but Coronaviruses in general, so there would be too many false positives to use this test in society to determine any policies.
1.) Nasal or throat swab testing (PCR) – will tell you if you have a currently active Coronavirus infection. 100,000 tests a day in the UK are being provided. This test looks for Coronavirus RNA. Sometimes not enough viral particles are picked up by the swab to be detected so someone with the virus may not be detected – a high false negative rate.THE USE: (Help to control the primary infection rate by getting people to self-isolate, and help healthcare workers provide the correct medicine to those severely ill).
2.) Antibody test (serology) – A blood draw which does not look for the actual virus but the body’s response to it, through the detection of antibodies (IgG). It may take up to 10-14 days for the body to produce antibodies so the timing of the test is also important. Again there are varying levels of specificity – IgG is more general, but testing for SARS-COV-2 will be more accurate. Four companies which have now developed antibody tests with a specificity of between 99-100%.THE USE: (Over time help determine the level of immunity and re-infection rate and help relax the lockdown).
IF YOU HAVE ALREADY HAD COVID-19 IT DOES NOT MEAN YOU WILL NOT GET IT AGAIN.
Unfortunately at the moment these tests will not tell you if you have lifelong immunity to COVID-19 after primary infection because it is too early to tell. The serology test will only tell you if you have an immune response, not how long it will last.
Testing needs to be conducted over a period of time and closely monitored if we want to work out the re-infection rate. However now we have these tests this is something starting to be measured. The hope is that these results will help to ease the government lockdown. These results will also help once a vaccine is developed to determine who would need it (those who have never been infected, or those who have been infected but have no antibodies – immunity).
Key Terms to understand:
2019- Novel Coronavirus (2019-nCOV) : Novel Coronavirus (used by the WHO when the virus first emerged in 2019)
Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) : This is the strain of Coronavirus that causes Coronavirus disease 2019 (COVID-19)
Coronavirus 19 (COVID-19) : This is the name of the disease caused by the virus.
