The health department has decided to start pool testing of samples for faster detection of positive and negative cases of Covid-19 across Calcutta.

In this method, samples of four to five persons will be mixed and then tested for quicker assessment of areas where the disease may have spread wide.

Primarily, at least 10 areas of Calcutta, including Belgachia, Garden Reach, Metiabruz, Tiljala, Tangra, Burrabazar and Rajabazar, have been identified for pool tests.

Virologists said swab samples of four to five persons are mixed and then put to test in a batch. If a pool test is positive, individual samples of the batch are retested.

And if a pool test is negative, all samples are considered negative.

The Indian Council of Medical Research has said in its advisory that pooling of more than five samples is not recommended to avoid dilution, which may lead to false negatives. The advisory has also said that as few as two samples can be pooled.

The test is carried out using the standard methodology of polymerase chain reaction after RNA extraction.

The health department has decided to set up camps where doctors, nurses and lab technicians will be present to draw swabs.

“We are focusing on certain areas of the city within containment zones, which have high density of population in clusters, for pool tests. If one sample of four to five persons turns out to be positive, it would be indicative of the spread of the coronavirus,” said a health department official.

“The pool test results will help us draw up the next course of action for these containment zones.”

Last available figures from the health department show Calcutta has 596 active coronavirus cases, highest among all districts of Bengal.

Of the 99 Covid-19 deaths across the state, Calcutta accounted for 64, according to information provided by the health department.

On Friday, the number of containment zones in Calcutta shot up to 326 from 319 on Thursday suggesting fresh evidence of the virus spread.

“In densely populated areas, pool tests will help us zoom in on specific wards in certain boroughs within the limits of the Calcutta Municipal Corporation,” a health department official said. “We have already collected data from the CMC’s health department to identify large cluster population where tests would have to start immediately.”