With the number of Covid19 cases spiking at a breakneck speed across the country, yesterday, the Indian Council of Medical Research (ICMR) issued an advisory on ‘pool testing’ — or multiple swab samples per kit — in low-infection areas. This is an attempt to scale up testing by increasing the capacity of laboratories to screen more samples in less time, using fewer resources.
The process of pool testing involves screening multiple swab samples in a single test. If a batch tests positive for Covid19, individual samples are tested separately to pinpoint the infected person. “This method is effective in two ways. First, it increases the capacity of testing, and second, it saves a lot of resources — time, cost and manpower,” Nivedita Gupta, senior scientist at ICMR, told ThePrint.
But, as per the ICMR, pool testing is only recommended in areas with a low prevalence of Covid19, which has been specified as two percent. However, in areas with an infection rate of two to five percent, pool testing may only be used for community survey, or surveillance, among asymptomatic individuals. For healthcare workers and individuals who have been in contact with confirmed Covid19 cases, the ICMR advised individual testing. And, for areas with positivity rates above five percent, the ICMR has strictly recommended against pooling of samples.
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“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,” Gupta said explaining how pool testing could turn into a logistical nightmare in areas where infection rates are high.
The ICMR has also cautioned against pooling of too many samples at a time citing the possibility of missing positive samples if the batch, cumulatively, has a low viral load. In a bid to avoid such false negatives, the ICMR has set the upper limit on pooling to five samples.
Crippled by a lack of resources, Andaman and Nicobar Islands had already begun conducting pool tests. “Five samples per testing kit are used. So, less than 25 kits are being used for testing 100 samples,” a government official said. Testing in India has, so far, been severely hampered by a lack of resources, and as a result, we have limited information on the virus’s true spread throughout India. Now, experts believe that pool testing can address that.
