The new sero-prevalence survey in the national capital will exclude those who were part the previous exercise and 25 per cent of the fresh samples in all districts will be taken from persons aged 50 and above, according to a standard operating procedure prescribed for it.
As per the SOP for the survey that began on Saturday, each sample collection team is to collect 25-40 samples per day.
"All districts are to ensure that out of total number of samples, 25 per cent are of those younger than 18 years of age, another 50 per cent are in the age group of 18-49 years and remaining 25 per cent of those in the age group of 50 years or more," reads the SOP prescribed by the Delhi's Directorate General of Health Services.
The fresh exercise is being undertaken for a comprehensive assessment of the COVID-19 situation in Delhi, but due to Eid holiday not many samples could be collected on Saturday, officials said.
Hence it has been decided to extend the survey till August 7, a senior official said on Saturday.
Originally, a five-day exercise from August 1-5, it will span all 11 districts of Delhi and cover various demographic segments.
Systematic Random Sampling methodology will be used for collection of samples with mandatory exclusion of individuals or households selected during the last sero survey conducted in June-July, the SOP says.
The survey began with samples collection from various districts, including North Delhi and Northwest Delhi, to start with on Saturday.
Sources said six districts are to be covered on Sunday.
According to the survey's standard operating procedure, "selection bias must be avoided" and any individual or household that was included in the previous round of sero-survey "must be excluded".
Teams in the field will collect the samples and will transport the samples the same day to the designated laboratories for processing. Sample collection must be completed latest by 2 pm so that samples reach the designated labs latest by 4 pm, reads the SOP.
As per a bulletin released on Sunday, Delhi recorded 961 fresh coronavirus cases, taking the tally in the city to over 1.37 lakh, while the death toll from the disease mounted to 4,004.
The active cases tally on Saturday was 10,356, down from 10,596 the previous day.
A senior government official on Saturday said 15,000 samples would be collected as part of this exercise, spanning different areas and age groups.
Representative samples will be taken from all the 11 districts.
A sero-prevalence survey involves testing the blood serum of individuals to check for the prevalence of antibodies against infection.
The last sero-prevalence survey was conducted by the Delhi government in association with the National Centre for Disease Control (NCDC) from June 27 to July 10.
It had found that around 23 per cent of the people surveyed had been exposed to the novel coronavirus, the central government had said.
The previous study had tested 21,387 samples.