MADURAI: The State government has approved pool testing for Covid-19 diagnosis in areas with 2-5 per cent positivity rate, said Health Minister C Vijayabaskar during an interaction with TNIE on Saturday. Pool testing is a method of testing samples of up to five individuals as one (pool). If the pool tests negative, all the samples in the pool are considered negative.
According to the guidelines of ICMR (dated April 13), if the sample pool tests positive, all samples in the pool must be tested separately by RT-PCR. Areas with more than 5 per cent positivity, health workers who were in direct contact with patients and known contacts of patients are not to be tested in this method.
The highest number of samples to be tested in a pool are kept at five due to higher chances of missing positive samples with a low viral load, if the pool size is increased beyond five, say microbiologists.
In an order dated July 17 by the Director of Public Health and Preventive Medicine Dr. TS Selvavinayagam, all nodal officers of government and private labs were told to implement pooled sample testing for COVID. The decision was taken to increase the testing capacity, early detection of COVID-19 cases in the community, cost-effectiveness and also to improve the turn around time (TAT) of the samples tested, it further read.
The Director, in another order (dated July 17) issued to the Deputy Directors of Health Services, Joint Directors of Rural Health Services and to Deans of government medical college hospitals, recommended pool testing for nasopharyngeal and oropharyngeal samples collected from asymptomatic frontline workers, markets and passengers from other countries or states or districts.
The orders also identified 21 districts including Kanniyakumari, Tirunelveli and Tenkasi in South Tamil Nadu, fit for pooled sample testing (based on the positivity rate as on July 16).
The list also includes Pudukkottai with the highest eligible positivity rate of 4.75%, Coimbatore, The Nilgiris, Dharmapuri, Namakkal, Salem, Krishnagiri, Karur, Tiruchy, Villupuram, Thiruvarur, Ariyalur, Perambalur, Thanjavur and Erode (with the least positivity rate of 0.86%).
Explaining the implementation of pool testing in Tamil Nadu, Health Secretary Dr. J. Radhakrishnan stated that in the 21 identified districts, those hailing from containment areas, close contacts and high-risk contacts would undergo individual testing only. In the rest of the districts, pool testing has been advocated for factory workers, office employees, frontline workers would be tested through pool testing, added he.
Selvavinayagam further directed the Deputy Directors to instruct block medical officers and medical officers in the field to collect samples from the above-said categories and to send them in cold chain to the designated RT-PCR laboratories, clearly indicating as 'Samples for pooled testing'.