Health expert warns of false negatives from COVID-19 rapid test

Wednesday, 2020-08-12 09:48:58
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Labour Hero, Prof., Dr. Nguyen Anh Tri.
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NDO – Those who have been tested negative for SARS-CoV-2 using rapid test should not be subjective as the method may lead to false results, Professor, Dr. Nguyen Anh Tri has affirmed.

>>> Hanoi plans to conduct extensive PCR testing for returnees from Da Nang

Nhan Dan Online had an interview with Labour Hero, Professor, Nguyen Anh Tri, Chairman of the Vietnam Society of Haematology and Blood Transfusion, to look into the correct understanding of COVID-19 tests as well as the need for all Vietnamese people to join hands in the fight against the epidemic.

Hailing the move from the Ministry of Health in changing from the COVID-19 rapid test to the Realtime-RT-PCR (rRT-PCR) method, as well as pooling the samples to reduce the time and costs required, Dr. Tri said that the SARS-CoV-2 virus is considered an antigen. A person infected with SARS-CoV-2 takes 7-15 days to develop antibodies to fight the virus.

“People infected with SARS-CoV-2 usually incubate for about 5-14 days (in some cases the incubation may be longer) before falling into COVID-19. But what is very dangerous is that during the incubation period, the carrier can already spread the virus into the community. Therefore, detecting people carrying the SARS-CoV-2 virus for timely isolation is important in order to limit the spread in the community,” Tri affirmed.

The rRT-PCR technique has been used around the world, and in Vietnam, in the test to detect the SARS-CoV-2 virus. Meanwhile, the rapid test – which is currently being used in some places – is used to detect antibodies to the coronavirus. It is not an appropriate technique as it is nonsense to use antibody detection test to find the antigen, said Tri.

“If the test result is positive, it still does not confirm if the person has antigens. Thus, the viral transmission may have already happened. In addition, if the test is conducted too early, the result is always negative, because antibodies always appear later,” Tri explained.

The most dangerous detail is that if the test result is negative, it is not known if the person has the virus in the body or not, the expert said, warning that those who get a negative result after their rapid test may think that they are not infected with the coronavirus or no longer carry the virus, leading to an increased risk of infection for themselves and also the community in the case that the SARS-CoV-2 virus is still in their body but has not fully developed into COVID-19 yet.

For that reason, Dr. Tri emphasised that the rapid test has no screening value in detecting the SARS-CoV-2 virus in people who have returned from epidemic-hit areas. The test is only used to monitor the results of treatment in people already confirmed as infected with SARS-CoV-2, showing whether they still have antibodies after treatment or not, and to serve epidemiological investigation in the community to see whether any people in a specific area have been infected with the SARS-CoV-2 virus or not, from which to build a proper strategy on epidemic prevention.

Tri also hailed medical staff in the central city of Da Nang – the current COVID-19 hotbed in Vietnam – in pooling samples taken from local residents for rRT-PCR testing to detect SARS-CoV-2, thereby speeding up the testing. They have been mixing approximately four samples and then performing the rRT-PCR test. In any positive batch, the samples then will be separated into four separate ones for further testing to identify the positive person. With this approach, the cost of testing will be reduced and the speed of testing will be given a boost, requiring about a quarter the length of the time needed for the no-pool method, Tri said.

He also suggested that those returning from the epidemic-hit areas should strictly follow the directions from the competent authorities in honestly and promptly making medical declarations. They must go to medical establishments to test if showing any abnormal signs, while complying with recommendations about wearing face masks, washing hands regularly and practicing social distancing.

Tri also stressed the need to localise and stamp out the outbreaks drastically, persistently and seriously. The rRT-PCR test should be actively carried out on those coming back from Da Nang, and other related persons in all provinces and cities across the nation as it is a decisive job to localise and stamp out the epidemic, Tri affirmed.

He suggested the Ministry of Health encourage both eligible public and private health facilities to participate in testing in order to reduce the cost for the rRT-PCR test (ranging from VND1.6- 2.2 million per test) and to boost the process by pooling samples as many countries around the world are doing.

Saying that Vietnam is still in control of the new outbreak after having recorded 99 days without any new community infections before, Tri said that the country was not surprised by the second wave that started from Da Nang.

However, this “leakage” is serious, according to Tri, as the new outbreak was caused by a modified foreign strain of the SARS-Cov-2 virus that spread much faster than other strains that have been detected in Vietnam. The epidemic happened in a big tourist city, amid the domestic tourism boom after a long social distancing period. In particular, it has happened first and foremost in hospitals where there are many critically ill patients.

“Whether this "leakage" becomes a "broken dike" or not depends much on our own attitude, determination and unanimity during this period,” Tri said.

Regarding the recent deaths in relation to COVID-19 in Vietnam, the former head of the Vietnam National Institute of Haematology and Blood Transfusion affirmed that they did not die directly from COVID-19 but in relation to the SARS-CoV-2 virus infection.

Not everyone infected with this virus will see it develop into COVID-19. They are mostly faced with a mild form of flu. Through studies around the world, only about 5-20% among them have COVID-19. But there is a high proportion of deaths in people with COVID-19, usually above 30%. “However, not all COVID-19 patients die. The treatment results from our first outbreak, with no deaths even with severely ill patients, has proved that point,” said Tri.

In Vietnam, all related deaths were with patients with very serious underlying diseases, combined with the SARS-CoV-2 infection. In patients with serious co-morbidities such as blood an cardiovascular diseases, diabetes and kidney failure, they have been undergoing treatment for a long time before being infected with SARS-CoV-2, meaning the risk of death from underlying diseases is higher for them, because of the adverse effects of the virus on the immune system and the patients’ resistance, Tri explained.

Therefore, the announcement on the death of such patients should be recorded as due to underlying diseases and tested positive for SARS-CoV-2 , or in the relation to the coronavirus as recommended by the World Health Organisation, Tri suggested.

It is only announced that the patients die from COVID-19 when they had only COVID-19 with no other associated illness, he said, adding that the correct announcement is very important to avoid causing unnecessary confusion while bettering the COVID-19 prevention and treatment for the targeted group of patients in hospitals.

Tri predicted that the current outbreak will not be easy to stamp out as it is estimated that about 1 million people have stayed or went through Da Nang within a month. The city has recorded the most infections during the new outbreak, while many other provinces and cities have recorded infected people returning from Da Nang.

“I think there will be more infected cases in the near future. At least 14-21 days must pass to learn about the scale of this outbreak. We know now not to be off guard but to be calmer and more determined to fight the epidemic.

“I want to emphasise that whether it’s quick or not in extinguishing the outbreak in Da Nang depends greatly on the public awareness and the whole community joining hands. The Government, the National Steering Committee for COVID-19 Prevention and Control and the Ministry of Health have done their best with the right and drastic directions and implementation of the disease control measures,” Tri concluded.