Context

The Indian Council of Medical Research (ICMR) has issued an advisory for using ‘pooled samples’ for testing of COVID-19. 

About

• The ICMR advisory added that the pool testing algorithm involves the Polymerase Chain Reaction (RT-PCR) screening of a specimen pool, comprising multiple samples.
• In case a pool tests positive, then each sample will be individually tested.
• The RT-PCR test is used to determine whether an individual has contracted Covid-19, caused by the SARS-CoV-2 virus.
• The objective of pool testing is to increase the capacity of laboratories to screen more samples in the same amount of time without doubling the resources needed.

Where it can be used?

• The test is only prescribed to be used in areas with low prevalence of the infection, i.e., with a positivity rate of less than 2 per cent.
• This means that of 1,000 samples in an area, if less than 20 have tested positive for Covid-19, the area is said to have a low positivity rate, and will qualify for pool testing.
• When the disease progresses and probability of positives goes up, the usefulness of the test comes down. One needs to repeat the tests, and conduct all tests individually, if the result is positive.

What the ICMR has recommended?

• ICMR has advised that while more than two samples can be pooled together, the number should not exceed five samples to avoid sample dilution, which can lead to false negatives.
• This method can be used in areas where the prevalence of COVID-19 is low, which means a positivity rate of less than two percent.
• In areas with a positivity rate between two to five percent, sample pooling of PCR screening may be considered in a community survey of surveillance among asymptomatic individuals.
• Andaman and Nicobar Islands and Uttar Pradesh have already embarked on pooled testing to enhance the testing capacity within limited resources.

Significance of pool testing:

• This method is effective in two ways.
  • It increases the capacity of testing
  • It saves a lot of resources — time, cost and manpower
• This method is useful when a country has a lower number of positive cases. In case a pool tests negative, all individual samples within the pool are considered to be healthy and not infected by Covid-19.
• Significantly, pooled screening can also help in tracking down the asymptomatic cases of the disease, thereby tracking community transmission.