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After the plan of conducting mass surveillance for Covid-19 through rapid antibody tests fell flat, Indian Council of Medical Research has now said that it will use it’s indigenously developed enzyme-linked immunosorbent assay (ELISA) tests to monitor the trend in the prevalence of infection at the district level.
Traditionally used in HIV and viral Hepatitis testing, ELISA tests are conducted in laboratory and measure level of IgG antibodies developed in an individual in response to viral infection.
The idea is too collect samples from persons who are not sick or show symptoms of Covid-19. ICMR will conduct testing in healthy individuals from low risk (outpatients and pregnant women) and high risk (healthcare workers) to understand how many of them test positive for Covid-19 to understand the prevalence of the virus in the district or in other words, to study community transmission patterns.
While earlier there were concerns with the accuracy of Chinese-make rapid kits being as low as 5 per cent, Lav Agarwal, Joint Secretary, Ministry of Health has stated that specificity of the new ELISA kits is 97 per cent and sensitivity is 92 per cent.
On selecting Ahmedabad-based Zydus Cadila to produce kits, Agarwal said, “There is a particular process to understand which organisation can undertake production at the faster pace, based on the organisation is selected and if need be in future other organisations will also be roped in.”
Up to 800 samples of persons who are not sick from every district will be picked up, the ICMR protocol states. From each district, up to ten health facilities, six public and four private will be selected, and outpatient department patients (who do not have any influenza-like illness), pregnant women and health workers will be chosen, to pick up the throat and nasal swabs for pooled RT-PCR tests (where 25 samples will be pool tested at one time) based on DNA technology and blood samples will be collected for ELISA tests based on antibody technology.
Steadily, ICMR has stated that the ELISA technique will replace RT-PCR technique for surveillance purposes. Currently, the RT-PCR technique is also being used because it is considered a gold standard, against which ELISA test of the same sample can be compared, the protocol states.
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