A day after the Centre announced that an IgG ELISA test for detection of antibodies to Covid-19 had been developed, it released a document outlining details of surveillance to be carried out in all districts to check for prevalence of the infection using the same.
The guidelines for state health departments to conduct the serosurveillance in collaboration with National Centre for Disease Control and Indian Council of Medical Research (ICMR) come three weeks after faulty rapid test kits brought from China were returned.
Along with the IgG (Immunoglobulin G) ELISA-based antibody detection tests, developed at the National Institute of Virology in Pune, reverse transcription polymerase chain reaction (RT-PCR) tests will be used to conduct the surveillance.
Antibody tests are blood-based tests chiefly used for surveillance and not diagnosis.
The guidelines stated that 10 health facilities from each district – six public and four private – should be selected to conduct the surveillance. Low-risk population such as outpatient attendees and pregnant women and high-risk population such as health care workers would be subject to the surveillance. Each month, 800 samples have to be collected, it further mentioned.
Throat and nasal swabs should be collected for RT-PCR tests and be tested in a one-time pool of 25 people. “Results of the sample pooling are only for surveillance purposes and it should not be used for diagnosis of individual patients,” the document stated.
Additionally, blood samples should be collected for detecting IgG antibodies for ELISA testing. In subsequent rounds of the surveillance, IgG ELISA-based testing of serum samples will replace RT-PCR based testing.
The health ministry said on Sunday that NIV Pune had validated the IgG ELISA test at two sites in Mumbai and had found that it had high sensitivity and specificity.
Joint Secretary of the Ministry of Health and Family Welfare Lav Agarwal said on Monday that the newly developed test’s specificity is 97% and sensitivity is 92%. “This kit can be used for epidemiological investigation and surveillance,” he had added.
Specificity refers percentage of results that will be correct if a person is not infected and sensitivity of a test is the percentage of result that correctly detects the infection.
The ELISA antibody test can enable testing of 90 samples together in a single run of 2.5 hours and the kit has an inactivated virus.
ICMR has partnered with the pharma company Zydus Cadila for production of the ELISA kits. After development at NIV-Pune, the technology was shared with Zydus Cadila.