Amid spurt in COVID-19 cases in India, the ICMR on Monday issued an advisory on the feasibility of using pooled samples for molecular testing of coronavirus as part of an effort to increase the number of tests in the country.
Sounding a note of urgency, the apex health research body said the number of COVID-19 cases in India is rising exponentially and in view of this, it is critical to increase the numbers of tests conducted by laboratories.
It said sample pooling for real-time RT-PCR screening for coronavirus is only recommended in areas with low prevalence of COVID-19.
"Positivity rate in cases is still low. Hence, it may help to use the pooled samples for screening. A pooled testing algorithm involves the PCR screening of a specimen pool comprising multiple individual patient specimens, followed by individual testing only if a pool screens positive,” the advisory said.
"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," it said while strongly discouraging pooling of more than five samples, except in research mode.
The objective is to increase the capacity of the laboratories to screen increased numbers of samples using molecular testing for COVID-19 for the purpose of surveillance, the ICMR said.
It said a feasibility study was conducted at DHR/ICMR Virus Research and Diagnostic Laboratory (VRDL) at King George's Medical University (KGMU) in Lucknow, where it has been demonstrated that "performing real-time PCR for COVID-19 by pooling five samples of TS/NS (200 ul/sample) is feasible when the prevalence rates of infection are low".
According to the advisory, all individual samples in a negative pool should be regarded as negative.
"Deconvoluted testing is recommended if any of the pools is positive. Pooling of more than five samples is not recommended to avoid the effect of dilution leading to false negatives," the advisory said.
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"The sample pooling for real-time RT-PCR screening for COVID-19 is only recommended in areas with low prevalence of COVID-19 (initially using a proxy of low positivity of 5 pc for COVID-19," the ICMR stressed.
"Preferable number of samples to be pooled is five, though more than two samples can be pooled, but considering higher possibility of missing positive samples with low viral load, it strongly discouraged to pool more than five samples, except in research mode," the advisory said.
With rise in coronavirus infections in India, the ICMR has taken into account the need to expeditiously expand COVID-19 testing facilities in all parts of the country and has initiated a proactive search of potential laboratories which could be enabled for coronavirus testing, a senior official said.
The ICMR has already invited applications from all government and private medical colleges for establishing COVID-19 testing facilities.
The government has identified 14 centres of excellence such as PGIMER in Chandigarh, AIIMS, New Delhi and NIMHANS in Bangalore to mentor all the government and private medical colleges in their catchment area to create state-of-art molecular virology setups.
The death toll due to coronavirus rose to 324 and the number of cases in the country climbed to 9,352 on Monday, according to the Union Health Ministry.
However, a PTI tally of figures reported by various states as on Monday evening showed at least 9,975 cases and 346 deaths.
There has been a lag in the Union Health Ministry figures, compared to the number of cases announced by different states, which officials attribute to procedural delays in assigning the cases to individual states.
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