Pooled samples will be tested for COVID-19 in 21 districts in Tamil Nadu where the positivity rate is less than 5%.
The Director of Public and Preventive Medicine has written to all nodal officers of government and private RT-PCR laboratories on testing pooled samples for COVID-19. The guidelines were already communicated to Deputy Directors of Health Services, deans of medical college hospitals, Joint Director of Health Services and nodal officers of laboratories in the State.
As per the guidelines, pooling of samples in a 1:5 ratio will be taken up in areas with a positivity rate of 2%-5% to increase the testing capacity, early detection of COVID-19 cases in the community and to improve the ‘turnaround time’ of the samples tested.
As on July 16, the positivity rate of less than 5% was observed in 21 districts as per the Indian Council of Medical Research (ICMR) portal data. These districts are deemed fit for pooled sample testing, the DPH said.
The districts where pooled sample testing will be undertaken (with the positivity rate in brackets) are: Pudukottai (4.75%), Tirunelveli (4.64%), Tiruchi (4.48%), Villupuram (4.41%), Tiruvarur (4.18%), Tenkasi (3.97%), Ariyalur (3.94%), Nagapattinam (3.63%), Perambalur (3.27%), Salem (3.12%), Kanniyakumari (2.84%), Tirupattur (2.52%), Krishnagiri (2.36%), Coimbatore (1.93%), The Nilgiris (1.79%), Thanjavur (1.73%), Dharmapuri (1.46%), Tiruppur (1.41%), Karur (1.38%), Namakkal (1.32%) and Erode (0.86%).
According to an advisory issued by the ICMR, a pooled testing algorithm involves PCR screening of a specimen pool, comprising multiple individual patient specimens, followed by individual testing only if a pool screens positive. All individual samples in a negative pool are regarded negative, resulting in substantial cost savings when a large proportion of pools test negative. The preferable number of samples to be pooled is five.
A district health official said that when samples were pooled, it helped in quicker testing compared to when individual samples were tested. “Individual samples will be tested if any pool tests positive for COVID-19,” he said.
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