As the Covid-19 pandemic spreads across the world, there is a massive demand for diagnostic and monitoring tests, which has led to a global shortage…
On Tuesday, the South African Medical technology industry issued a statement warning the public about the use of Covid-19 “self-tests” that have entered the market.
“The SA Medical Technology Industry Association (SAMED) and the Southern African Laboratory Diagnostics Association (SALDA) – want to contribute to informed discourse relating to the use of medical technologies, including tests for COVID-19,” said the statement.
“Members of the public who might want to use them should be cautioned that the quality and efficacy of these products are unknown.”
Testing should be done by professionals in accredited labs
Emphasising this message, Sarah Cohen, SALDA’s Executive Officer says: “All testing for Covid-19 should be done by healthcare professionals in an accredited laboratory or approved facility, with all the relevant quality control measures in place.”
2 Tests currently being used by professionals:
At present, two main types of tests exist for COVID-19: those that detect the presence of a virus; and tests that can detect previous infection and the body’s immune response to the virus.
- A PCR (polymerase-chain reaction) laboratory-based molecular test must be performed in equipped laboratories by trained staff. A PCR test looks for the virus when an individual is suspected of having an infection.
- Throat or nose swabs are used as samples to test for the virus in a laboratory. If the test shows a positive result, it is an indicator that the patient has the virus and that the individual is likely to be infectious.
- The PCR test can give a negative result – including a “false negative” – if the test was done during the time (a window period) when the individual’s viral load was too low to be detected.
“The negative results do not rule out infection or that a person can infect others. Based on the current data, patients with COVID-19 are infectious for up to two weeks from the time when they acquire the infection,” says Cohen.
- A serological test is designed to detect the immune response against the virus.
- This indicates that a person has had an infection before.
- One such test, sometimes referred to as a “rapid test”, entails a finger prick and checking for the presence of antibodies in the person’s blood. This type of test cannot be used for diagnosing an active COVID-19 case.
No evidence for immunity
Currently, there is not enough evidence to show whether the presence of antibodies to SARS-CoV-2 gives immunity to subsequent infection by this virus in humans. The development of antibodies to a pathogen through natural infection is a multi-step process that typically takes place over 1-2 weeks, but the process to develop a full immunologic response may be longer.
Most COVID-19 studies on the presence of antibodies to date show that people who have recovered from infection have antibodies to the virus. However, some of these people have low levels of antibodies which may not be enough to neutralise the virus in their blood if they are exposed to it again.
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