The National Institute for Communicable diseases (NICD) says the ability of the Covid-19 coronavirus to mutate – its ability to alter its genetic material and therefore circumvent test results – is, for now, “not a big problem”.
The NICD’s professor Cheryl Cohen told City Press that it was possible for patients who tested negative before to test positive in later tests.
But, she said, this was not related to the issue of the virus being able to change form and circumvent test results.
“During the incubation period, which is the time between being infected by the virus and becoming ill, the virus can be at levels in the body that are too low to be detected by the tests until the person actually becomes ill.
“This is why we recommend testing only symptomatic people because a negative test does not exclude infection.
“Importantly, if you are supposed to self-quarantine for 14 days you must still do this even if you have a negative test,” she said.
Cohen said mutation was a response by the virus to ensure survival in a certain setting.
“In other words, it adapts to new hosts and environments.
“Some viruses, like influenza especially, have a reputation for being able to mutate easily.
“The Covid-19 virus has shown low levels of mutations since it emerged,” she said.
“The virus has not mutated substantially and there is no problem with the polymerase chain reaction (PCR) tests which we use to test mutations.”
She said mutation happened naturally with some viruses as they spread between people and Covid-19 could not be discounted.
“Fortunately, at this time, this is not a big problem for the coronavirus,” she said.
“If a person is sick and they test negative … it means the sickness is not caused by coronavirus. If they get sick again they will need to be tested again,” Cohen said.
In terms of an internal government communication City Press has seen, global indications showed that finding a vaccine for the virus could prove a challenging task because of its ability to mutate.
The mutative nature was suspected to be behind the cases in which some blood test results sometimes changed from negative to positive and vice versa.
Recently, a group of 114 South Africans were evacuated from Wuhan in China – the epicentre of the coronavirus outbreak – after delays related to previous tests that were apparently ambivalent for eight members of the group.
With the virus’ proven ability to change form, close monitoring of those whose tests were uncertain was expected to be a serious concern for the government, according to the confidential communiqué.
However, according to News24, Zweli Mkhize, the health minister, said at the time that each member of the group had already tested negative for coronavirus before boarding the flight from Wuhan.
Anyone who would have tested positive before boarding the chartered plane would have been referred to the Chinese health system, Mkhize said.
Cohen said other than the PCR tests, there were other types of tests, called serology tests, that were used to look for the presence of antibodies, which the body makes to fight the virus.
“These tests are not very useful to tell if a person who is sick now has Covid-19.
“In future they might have a role for telling which people have already contracted Covid-19,” she said.