How pooled testing works, when it helps

GS Paper III

Topic: Science and technology

Prelims: Pooled testing

What’s the News?

Faced with criticism about insufficient testing and the reality of limited resources, India has decided go for pooled testing in districts where no cases have been reported. This would on the one hand give data on whether these really are zero-case districts, and on the other, save resources.

Pooled testing:

  • It is a method of testing several samples together with the same technique (RT-PCR) that is being currently used to test individual samples.
  • Samples taken from the nose or throat are pooled together by suspending them in a solution in laid-down proportions.
  • The remaining samples are then labelled and kept separate. Pooled samples are subjected to a test; if it is negative then all samples in the pool are cleared.
  • If it is not, then individual samples are tested to find out which one is positive.

Indian Council of Medical Research say on pooled testing:

  • Number of COVID-19 cases in India is rising exponentially. In view of this, it is critical to increase the numbers of tests conducted by laboratories. Hence, it may help to use the pooled samples for screening.
  • As all individual samples in a negative pool are regarded as negative, it results in substantial cost savings when a large proportion of pools tests negative.
  • The idea, it said, is to increase the capacity of laboratories to screen more samples for surveillance rather than diagnostic purposes.

Pooled testing use:

  • The ICMR document is clear that pooled testing is only to be used in “areas with low prevalence of COVID-19 (initially using proxy of low positivity of <2% from the existing data). Still a watch should be kept on increasing positivity in such areas.
  • In areas with positivity of 2-5%, sample pooling for PCR screening may be considered only in community survey or surveillance among asymptomatic individuals, strictly excluding pooling samples of individuals with known contact with confirmed cases, Health Care Workers (in direct contact with care of COVID-19 patients). Sample from such individuals should be directly tested without pooling.
  • The ICMR does not recommend pooling in areas where positivity rates exceed 5%. Government sources, though, say pooled testing is currently being considered only in the districts from where no cases of COVID-19 have been reported so far.
  • This is to be done in areas where the rate of seropositivity is less than 2%. This helps clear more people with fewer tests.
  • So far private hospitals are concerned; this is not exactly for individual diagnosis. Using it like that should affect the testing charges. Private hospitals should think about this.

Pooled testing other use areas:

  • In the US, pooled testing is being used in some areas to test population-level infection rates. For example, scientists from Stanford Medicine used it to estimate the prevalence of the disease in the San Francisco Bay Area while conserving scarce testing resources.
  • It can be used for any disease whose test involves, like COVID 2019, an RT-PCR test, and is routinely used for HIV screening purposes.
  • Pooling strategies have been used to reduce the costs of polymerase chain reaction-based screening for acute HIV infection in populations in which the prevalence of acute infection is low (less than 1%).
  • Only limited research has been done for conditions in which the prevalence of screening positivity is higher (greater than 1%). It is a well-recognised “screening tool” for epidemiologists.

Remdesivir: hope, with caution

GS Paper III

Topic: Science and technology

Prelims: RdRp enzyme

What’s the News?

The drug remdesivir has been under the spotlight as a possible treatment for critical cases of novel coronavirus disease (COVID-19). Globally, it is one of the four possible lines of treatment being investigated in the Solidarity trials under the aegis of the World Health Organization (WHO).


  • It is a drug with antiviral properties that was manufactured by US-based biotechnology company in 2014, to treat Ebola cases.
  • It was also tried in patients of MERS and SARS, both caused by members of the coronavirus family, but experts said it did now show promising results back then.

Its work:

  • Coronaviruses have a single-strand RNA as their genetic material. When the novel coronavirus SARS-CoV2 enters a human cell, an enzyme called RdRP helps the virus replicate. Remdesivir works by inhibiting the activity of RdRP.
  • When the virus engulfs itself around a human cell, it injects its RNA inside the cell. The RdRp enzyme causes viral replication. Remdesivir inhibits the enzyme and stops further replication.


  • A small cohort study published in The New England Journal of Medicine on April 10 used remdesivir on 61 patients in USA, Canada, Europe and Japan.
  • The study found clinical improvement in 68% of the cases, with their oxygen levels improving; 47% patients could be discharged after treatment, and more than 50% patients (17 of 30) no longer required mechanical ventilator support.
  • The study found that clinical improvement was less frequent in patients on invasive ventilators or among elderly people. Seven patients died despite treatment with remdesivir.

India’s stand on remdesivir:

  • The Indian Council of Medical Research (ICMR) has said it can consider using the drug if local manufacturers are willing to procure it. Remdesivir is currently not available in India.
  • The ICMR plans to wait and watch for the results of WHO’s Solidarity trials to make an assessment on the efficacy of remdesivir for COVID-19 treatment.
  • The study had no control arm, meaning another group of patients who were not administered the drug, to compare outcomes of treatment with and without remdesivir. Unless such trials are conducted, the effect of the drug remains a grey zone.

Reasons behind remdesivir being studied:

  • Currently, there are about six trials and studies being done globally for remdesivir. China has initiated two clinical trials using remdesivir in multiple sites in Hubei province, the worst hit with COVID-19. One study will focus on critically ill patients with low oxygen levels. The other study will focus on patients with moderate symptoms.
  • In the US, the National Institutes of Health has started a phase-II randomised placebo-controlled trial for adult patients. In France, the INSERM research institute is conducting a study to evaluate potential treatments for COVID-19; these include remdesivir.
  • Gilead is also running a phase-III trial in the US, Asia and Europe.

Other lines of treatment being investigated:

  • Hydroxychloroquine, an anti-malarial drug, is undergoing multiple trials to assess if it can be used to treat severe COVID-19 cases. It works by decreasing the acidity in parts of the cell where the virus is present, thereby inhibiting it.
  • Again, ritonavir and lopinavir are two antiviral drugs used for treatment of HIV. These too work by inhibiting the virus;s RNA. Specifically, they target the enzyme that helps the virus split proteins.
  • These two drugs are being used in India and several countries for seriously ill patients. In HIV patients, these two antiviral drugs work together to decrease the viral load in blood. Their use in COVID-19 patients seeks the same outcome. But so far, it has not shown great success in viral suppression.
  • In Wuhan, a clinical trial on 199 patients published in The New England Journal of Medicine on March 18 did not find a clinical difference between patients given ritonavir-lopinavir and those not given the combination.


  • No definitive conclusions can be drawn from these data but he encouraged further controlled trials to validate the treatment potential of remdesivir.
  • But the Ebola and coronavirus are different. We should wait for the trials to measure the efficacy of the drug for COVID-19.

Goa is now COVID-19-free

GS Paper III

Topic: Science and Technology

Mains: three zones depending on number of virus

What’s the News?

Goa on 19th April 20, 2020 became the first zero COVID-19 State in the country with the last seven positive cases also turning negative.

Three zones:

  • The Centre is likely to categorise the country into red, orange and green zones depending on the number of coronavirus cases during the proposed extended period of lockdown and might allow limited services to function in the safe zones.
  • There will be no activity in the red zones — the districts where sizeable number of cases were detected or areas which were declared hotspots.
  • In the orange zones — where only a few cases were found in the past with no increase in the number of positive cases — minimum activities like opening of limited public transport, harvesting of farm products will be allowed.
  • Green zones will be in the districts where there is no COVID-19 case.

Goa- first Green state:

  • This makes Goa the first green State in the country with no case of coronavirus being reported from April 3. The coastal State had a total of seven positive cases, of whom six had travel history and one was the brother of a positive patient.
  • Goa is now COVID-19-free, all seven patients have tested negative. They will be quarantined at government facility and later at home.

Maintaining Green Zone:

  • To ensure that we remain a zero COVID-19 State. The lockdown will continue till the Central government decides. Our borders with Maharashtra and Karnataka will continue to remain sealed. Anyone entering the State under special circumstances will have to stay in a government quarantine centre.
  • Social distancing will have to be maintained. State transport buses will ensure this while shifting government staff. Two-wheelers will have a single occupant and 1,000 thermal guns will be positioned at various places

Seafarers issue:

  • The Centre is also considering a policy of getting back lakhs of Indians who are overseas, beginning with those employed on the ships first and the Centre would be announcing the repatriation mechanism any time.
  • Once the government makes the mechanism official, it will take about 3-4 days for the first lot of seafarers to return.
  • Those already at Indian ports or closest to the coast will return first. For the rest, discussions are on whether it would be the sea route or air route that would be taken to get them back.
  • All these seafarers would be subjected to government quarantine followed by home quarantine. Goa has made available 8,000 rooms for Goan seafarers.


  • Though Goa was the first Indian State to be free of any tested positive case and a happy moment for everyone, especially the frontline workers, it was important to realise that this was no time for relaxing.
  • The government would scrutinise reports of its three-day door-to-door citizens survey done last week and decide on testing people for COVID-19 wherever felt necessary.