Why rapid tests are doing more harm than good

Doctors in Jumla collects swab of a patient on 7 April. Photos: DHIRAJ GURUNG

On 13 April, the nose and throat swab of a woman in Kailali district tested positive for the COVID-19. The 65-year-old who was in quarantine had previously tested negative in a Rapid Diagnostic Test (RDT) and sent home.

But only three days later, a Polymerase Chain Reaction (PCR) report confirmed that she was infected with novel coronavirus, upon which she was taken to Seti Provincial Hospital for isolation. She is one of the eight people who had their swab and blood samples collected for both RDT and PCR, but officials didn’t wait for the PCR report.

“She should not have been sent home without waiting for the PCR report confirmation. It was a grave mistake because she could have spread the virus after coming out of quarantine,” says Sameer Dixit, researcher at the Centre for Molecular Dynamics in Kathmandu.

In fact the RDT can show false negatives in people for up to a week after infection because their bodies have not produced sufficient anti-bodies to be detected. In fact, public health officials say Nepal should have gone directly for PCR like Korea and other countries instead of RDTs.

As of 16 April, 15,800 people have been tested for COVID-19, using both RDT and PCR. But a lack of distinction in the specificity of the two test methods in the public consciousness has led to unnecessary panic and stigmatisation of people and entire communities.

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Health workers in Lalitpur conduct rapid diagnostic tests on 14 April for people who have come from abroad recently. Photos: BIKRAM RAI

The rapid diagnostic test can only monitor if an individual has developed antibodies to fight against the COVID-19, and can be detected only a week after infection and for at least six months after. The test cannot identify the virus itself and therefore cannot verify if the person has an active infection.

When the virus enters a human body, the body’s natural immune system is activated and secretes a protein to kill the virus called antibody. There are two types of antibodies: Immunoglobulin G (IgG) and Immunoglobulin M (IgM). It takes at least six days for IgM and 15 days for IgG to develop after a virus enters the body.

RDT kits being used to test COVID-19 can detect both types of antibodies, which is why rapid tests conducted in the early stage of infection will give a negative result even if the individual is actually infected. The case in point is the patient from Kailali who took a RDT before it could have detected the virus. The real-time PCR however was able to detect the coronavirus in her swab sample.

“Tests conducted without proper scientific knowledge and guidelines will do more harm than good,” stresses lab specialist Umesh Prasad Gupta.

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Nepal has not yet developed a protocol to guide healthcare workers conducting mass testing for COVID-19, and the government’s decision to use RDT for mass testing actually contradicts the WHO recommendation and the Indian Council of Medical Research (ICMR) guidelines.

Those protocols require RDT to be conducted only for individuals who have undergone 14 days of quarantine, healthcare workers, or for people placed in isolation in hospitals. And even if the result turns out to be negative, a retest with PCR is mandatory. High risk patients are to be placed under quarantine until the PCR confirmation.

On the other hand, if a suspected individual tests negative in PCR, he/she should still be placed in quarantine and undergo RDT after 10 days. Only if the second test is negative, is the person to be released.

The WHO has also recommended countries to use the real-time PCR for the COVID-19 testing because RDT is only 86% sensitive, and cannot detect new infections.

However in Nepal, the Office of the Prime Minister and Cabinet on 4 April directed the health ministry to retest all people whose blood samples tested positive on RDT. The Health Ministry also decided to retest 20% of all negative RDT with PCR, when in fact PCR should have been the basis of further investigation.

On 1 April, the Ministry of Health instructed that 75,000 RDT kits imported from China by a private contractor not be used because of doubts about their reliability. The importer, Omni Business Corporate Internaitonal (OBCI) was also accused to inflating the cost of the kits and using its connections to the Prime Minister Oli to do the deal on 25 March.

The Department of Health also announced on 2 April that it had cancelled the contract with Omni and confiscated its Rs50 million deposit. However, it looks like Omni is still in business and the Department said 30,000 of the rapid diagnostic kits that Omni brought are the ones being used all over the country to test people who have come from abroad recently.

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