The Indian Council of Medical Research (ICMR) has recommended the use of pooled samples as a potential strategy for increasing molecular testing capacities for Covid-19, amid surging case numbers in India. The advisory emphasized that expanding the volume of tests carried out in Indian laboratories is crucial in the combat against the ongoing virus.
Understanding Pool Testing
Pool testing, also known as grouped sample testing or batch testing, is a technique used to increase the capacity and efficiency of virus testing. This testing algorithm involves using the Polymerase Chain Reaction (PCR) method to screen a pool created by combining multiple individual patient specimens.
If a pool tests positive, each sample within that pool undergoes further individual testing, a process often referred to as pool de-convolution. However, if the pool tests negative, all individual samples within it are also regarded as negative. This streamlined approach results in significant resource savings, especially when a large fraction of the total tested pools turn out negative. Two distinct benefits of this method are observed: firstly, it exponentially enhances the testing capacity, and secondly, it optimizes resource utilization in terms of time, cost, and manpower.
Advisory on Maximum Number of Samples
The ICMR advisory specifically warns against pooling more than five samples at a single time. The rationale behind this limitation is that exceeding this number could risk diluting the viral load, which might consequently produce false negatives.
Correlation between Pooling and Positivity Rates
The advisory introduces different approaches to pooling based on the varying prevalence of Covid-19 cases in different areas. According to the ICMR, these approaches can be broadly classified into three categories, as follows:
1) Pool testing should ideally be implemented only in areas with a low prevalence of Covid-19. This can initially be determined using previously established data that shows a positivity rate of less than 2%.
2) In regions with a positivity rate between 2-5%, pooled testing may be employed for community surveys or surveillance among asymptomatic individuals. However, it is vital to exclude samples from individuals who have had confirmed contact with Covid-19 patients and healthcare workers directly involved in treating Covid-19 patients. The samples from such individuals should be sent for ungrouped testing.
3) Areas or populations recording positivity rates of over 5% for Covid-19 are not suitable for the implementation of pooled testing.
The ICMR’s strategic suggestion employs a blend of sensitivity to local infection rates and resource optimization techniques to manage India’s response to the Covid-19 pandemic effectively. Its focus on resource conservation while working towards increased testing volumes demonstrates adaptability in the face of challenging circumstances.
