Over 24k samples collected for random antibody tests
The Indian Council of Medical Research’s (ICMR) has collected around 24,000 blood samples from 60 districts in 21 states over the past two weeks for a sero-survey (a test of blood serum) to check for exposure to the Sars-Cov-2 virus that causes the coronavirus disease (Covid-19) in the general population.
The cross-sectional survey of adults aged 18 years or more will detect infection in the community by testing for the presence of antibodies against Sars-CoV2 that are found in the blood of people who have recovered from it.
Representative samples were taken from 60 districts chosen from among four categories based on reported Covid-19 cases per million population -- zero, low (0.1-4.7), medium ( 4.8-10) and high (>10). Four hundred samples from 15 districts from each stratum were selected randomly, according to ICMR.
The first batch of about 70% samples was dispatched to a central laboratory in Tamil Nadu for analysis on Sunday, and the results are expected in about three weeks.
“By end of this week the Indian Council of Medical Research (ICMR)-National Institute for Research in Tuberculosis in Chennai (Tamil Nadu) that has been identified as the central lab to do the analysis, should receive all samples,” said an ICMR official, who did not wish to be identified.
This community-based survey will hold the key for getting several vital clues on the disease trend, testing and so on in the country, experts said. “If more people have antibodies and never detected that means the infection is widely present. It is a good thing that only few are getting ended up with complications and death. Indirectly it is also a way of knowing whether enough tests are being done,” says Dr Girdhar R Babu, head, life course epidemiology, Public Health Foundation of India .
The blood samples will be tested for IgG antibodies using ELISA method (IgG is an antibody that develops later as compared to the other antibodies and therefore confirms a past infection). ELISA is an enzyme-based laboratory test that detects and quantifies antibodies in blood.
The 21 states from where samples have been taken are Andhra Pradesh, Assam, Bihar, Chhattisgarh, Gujarat, Jharkhand, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Odisha, Punjab, Haryana, Rajasthan, Tamil Nadu, Telangana, Uttar Pradesh, Uttarakhand, Himachal Pradesh, West Bengal, and Jammu & Kashmir.
Additionally, about 5,000 samples have been picked from 10 hotspot cities with maximum case load: Mumbai, Delhi, Chennai, Ahmedabad, Thane, Pune, Indore, Kolkata, Hyderabad, and Aurangabad.
“Conducting population-based sero-surveillance for Sars-CoV-2 will estimate and monitor the trend of infection in the adult general population, determine the socio-demographic risk factors and delineate the geographical spread of the infection,” said a recently published ICMR document.
It added: “Such serosurveys repeated at regular intervals can also guide containment measures in respective areas. State-specific context of disease burden, priorities and resources should guide the use of multifarious surveillance options for the current COVID-19 epidemic.”
“We are likely to repeat the survey depending on what results we get,” said the ICMR official.
Apart from the sero-survey, the Union health ministry has a hospital-based active surveillance plan using reverse transcription-polymerase chain reaction (RT-PCR) tests among healthcare workers, outpatient department patients, and pregnant women in all districts. At least 10 hospitals--six public and four private --will be selected from each district for the sampling, with an overall target of lifting 800 samples a month.
These two surveys are in addition to the random testing of about 250 severe acute respiratory infection (SARI) and influenza-like illness (ILI) cases that the Centre has advised all states to conduct in each district.