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Coronavirus pandemic: When to test and whom

On Monday, the World Health Organisation (WHO) tweeted a plea from its Director-General Tedros Adhanom Ghebreyesus: “Once again, our key message is: test, test, test.”

Scientists at work at the National Institute of Virology, Pune, last week. (Express Photo: Pawan Khengre)

Why is testing considered important in an outbreak of this kind?

To have an idea of the number of infected people and therefore, a clear picture of the magnitude of the crisis. Testing is necessary to isolate infected individuals so that they can be treated quickly and effectively — and be kept from infecting others. Patterns in test results help in understanding how the disease is evolving, and in taking evidence-based measures to check the rate of infection.

All of this is especially relevant because SARS-CoV-2 is extremely infectious. The contagion has now touched nearly 1.8 lakh people in 144 countries, and killed over 7,000. Every infected individual is expected to infect between two and three others on average.

The virus has an incubation period of 14 days, which means that a person who has caught it may carry and transmit it for up to two weeks without showing any symptoms. A seemingly healthy person sitting beside you in the Metro could theoretically be carrying the virus, and might transmit it to you.

On Monday, the World Health Organisation (WHO) tweeted a plea from its Director-General Tedros Adhanom Ghebreyesus: “Once again, our key message is: test, test, test.”

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So, why are some countries testing fewer people than others?

India and the United States are testing far fewer people than China and South Korea did. South Korea’s strategy of mass testing is currently seen as being highly successful — however, testing at such scale in a country India’s size is a whole new ball game.

Every country’s decision on whom to test, when and how many, is guided not only by clinical guidelines and technical competence, but also by the trajectory of the disease’s spread, the mode of transmission — whether imported, local, or community transmission — and, very importantly, by the availability of resources.

Coronavirus pandemic: Outside a testing facility in New Delhi. (Express Photo)

In its interim guidance on “Laboratory testing for coronavirus disease 2019 (COVID-19) in suspected human cases” on March 2, the WHO said: “The decision to test should be based on clinical and epidemiological factors and linked to an assessment of the likelihood of infection. PCR [polymerase chain reaction] testing of asymptomatic or mildly symptomatic contacts can be considered in the assessment of individuals who have had contact with a COVID-19 case. Screening protocols should be adapted to the local situation.”


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India is currently testing only symptomatic people with contact or travel history, but the Indian Council of Medical Research is set to widen the net. To check for evidence of community transmission, it will test 1,000 people with symptoms but no corresponding history of travel or contact with an infected person.

But what is the reason that India is testing slowly, selectively?

Central and state governments have already taken steps to ensure social distancing by shutting down schools, colleges, and cinema halls. Visas have been cancelled to keep foreigners out. Though acutely aware of the threat, the thinking within the government is that 114 cases (until Monday) in a country of 1.3 billion is not an alarming number.


So long as the chain of infection is clearly established, the virus is not considered to have entered the phase of community transmission. Until the health system detects someone whose source of infection cannot be traced, mass testing is not necessary. The test is free for individuals, but it is not inexpensive — there are two tests in all, and each sample costs the government a total Rs 5,000.

Doctors attend to patients at a Homeopathic Hospital in New Delhi. (Express Photo: Tashi Tobgyal)

“We are testing people with symptoms or contact or travel history. We do not want to spread panic. We will test those that need to be tested,” Lav Agarwal, joint secretary in the Ministry of Health, said on Monday. A total 63 laboratories are now carrying out tests, and another nine labs will open soon. Two lakh testing kits are being procured to supplement the original stock of 1 lakh.

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Dr K S Reddy, president of the Public Health Foundation of India, said: “Testing needs to to be stepped up in stages, initially prioritising persons with a high probability of being infected… Mass screening is not feasible and indiscriminate testing is counterproductive, giving a false sense of security to those reported negative, as they can still be infected if they are exposed later. A network of qualified public and private labs can follow well defined protocols for testing suspected cases. These criteria can be revised based on the course of the epidemic and the availability of certified kits.”

And what exactly is the test, and how is it carried out?

A virus is neither living nor non-living. Once inside the host cell, it replicates. The genetic material — RNA in the case of the novel coronavirus — is the key to its identification.


According to the WHO, routine confirmation of cases of COVID-19 is based on detection of unique sequences of virus RNA by Nucleic Acid Amplification Tests (NAAT) such as real-time reverse-transcription polymerase chain reaction (rRT-PCR), with confirmation by nucleic acid sequencing when necessary.

Dr Partha Rakshit, head of the microbiology laboratory at the National Centre for Disease Control, explained: “We cannot see the virus, so we try to detect its genes in a sample. The first test narrows down the identity of the virus to the coronavirus family. This is a screening test. In the next test, we try and detect genes that are specific to the novel coronavirus. The second test is done only when the first is positive.” The second test is a genome sequencing test.


Also read | ICMR senior scientist: ‘Have 1.5 lakh test kits and have ordered 1 million more’

The run time of each test is about 2 hours. However, the extreme precautions that need to be taken in sample transportation, preparation, etc. mean that the total time taken for both tests is about 8-9 hours. The government has decided to not notify a person as coronavirus positive until both tests are positive.

First published on: 17-03-2020 at 12:57:32 am
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