There’s only one way to test for Covid-19: experts

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There’s only one way to test for Covid-19: experts

Beware of money-hungry manufacturers offering quick-result tests

Senior science reporter
The only way to test if people are infectious is with a polymerase chain reaction (PCR) test, where a swab is taken from a person's nose and sent to a lab.
NOSE FOR TESTING The only way to test if people are infectious is with a polymerase chain reaction (PCR) test, where a swab is taken from a person's nose and sent to a lab.
Image: AFP/Lakruwan Wanniarachchi

Antibody tests have changed the face of our understanding of how widespread Covid-19 is, but local experts have cautioned that their use is for modelling data only.

They should not be used to determine if you’re actively infectious and a danger to others.

Also, no such antibody tests are licensed in SA, meaning anyone claiming to do them here would be doing so illegally.

PCR (polymerase chain reaction) tests for Covid-19 involve a nasal swab that is sent to a laboratory for testing. There, technicians search for the active presence of the virus.

Antibody tests, on the other hand, test for the presence of antibodies in your blood (or sputum) to see if you’ve had an immune response to the virus. 

Within that group are rapid antibody tests which, as the name suggests, have the quickest turnaround time and are earmarked for point-of-care facilities, such as chemists.

Antibody tests abroad have in the past few days augmented other global research (in the US, China and Iceland), showing that infections are up to 85 times higher than we thought and that the death rate is thus much lower.

The research suggests that a great many asymptomatic people have had the virus, but for obvious reasons, never presented for testing.

It is great that SA is a few weeks behind many other countries with our epidemic curve, as we can learn from their experiences and adjust our measures accordingly.
Prof Wolfgang Preiser

Prof Wolfgang Preiser, a virology expert at the University of Stellenbosch, said that “antibody tests will have a role to play” and that “it is great that SA is a few weeks behind many other countries with our epidemic curve” as “we can learn from their experiences and adjust our measures accordingly”.

However, not all antibody tests are reputable.

“We also know that many of the tests being marketed [overseas] are not good. So before one launches into using them it will be important to assess their performance,” he said.

“A particular issue is rapid antibody tests,” he added.

Their sensitivity “is usually lower than that of lab-based tests, so offering them as a panacea, as some moneymakers are trying to do, is very misleading and bad.”

Preiser said the use of antibody tests to declare someone “safe” (had the infection, recovered and is now immune) is premature at this stage. 

“Neither do we know a lot about immunity ... but the good news is that so much is going on in this field that we should learn more pretty soon,” he told Times Select.

Prof Shabir Madhi, from Wits University and head of the public health subcommittee that is advising President Cyril Ramaphosa and his cabinet in our Covid-19 response, said: “There are different tests out there, but the only way to test if people are infectious is with a PCR (polymerase chain reaction), in which case a swab taken from your nose is sent to a laboratory.”

He said there are antibody tests that look at the body’s immune system, “but none are licensed in SA” so anyone doing it here is “doing so illegally”.

He added: “The use of an antibody test is very limited and doesn’t tell if you’re infectious or not. The purpose is to inform us who might have been infected in the past, and this means they might be protected from getting it again. We can use it as a tool to try to identify the true rate in communities, but it has a very specific utility. It has not been approved and cannot identify who is infectious.”

Dr Kerrin Begg, a global expert at University of Stellenbosch, said there would be “challenges” with “antibody testing this early in an epidemic” in SA.

“One of the challenges is that not all antibody tests are equal in terms of accuracy and reliability,” she said, cautioning that false positive and false negatives could make their way into the picture.

One of the challenges is that not all antibody tests are equal in terms of accuracy and reliability.
Dr Kerrin Begg

The World Health Organisation (WHO) applauds efforts to upscale testing, but cautions against rushing into things.

“In response to the growing Covid-19 pandemic and shortages of laboratory testing capacity, multiple diagnostic test manufacturers have developed and begun selling rapid and easy-to-use devices to facilitate testing outside laboratory settings.”

WHO said it “applauds the efforts of test developers to innovate and respond to the needs of the population”, but that “before these tests can be recommended, they must be validated in the appropriate populations and settings”.

Inadequate tests may “miss patients with active infection” or “falsely categorise patients as having the disease when they do not, further hampering disease-control efforts”.

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