Testing strategies for the virus

Updated - April 15, 2020 11:33 pm IST

Published - April 15, 2020 11:31 pm IST

Dr. Saranya Narayan, Senior microbiologist

Dr. Saranya Narayan, Senior microbiologist

The year 2020 has started on a very challenging note for all of us. The world woke up to a new infection, COVID-19 caused by the SARS-CoV-2 virus. The virus was so named as it is almost similar to the SARS virus and like it, is an RNA virus belonging to the family of Corona viruses. The virus though milder than the SARS virus is easier to transmit.

The Indian Council of Medical Research (ICMR) and the State health authorities have issued notifications and guidelines for testing strategies that every testing laboratory and treating hospital need to abide by.

Who can get tested:

ICMR modified testing strategy issued on 9th April.

Tests can be done for:

All symptomatic individuals who have undertaken international travel from the 6th of March

All symptomatic contacts of laboratory confirmed cases.

All symptomatic healthcare workers.

All hospitalised patients with Severe Acute Respiratory Illness (fever and cough and/or shortness of breath)

Asymptomatic direct and high-risk contacts of a confirmed case should be tested once between day 5 and day 14 of coming in his/her contact.

In hotspots/clusters or large gatherings/evacuees centres, anyone with Influenza like illness (ILI) ie fever, cough, sore throat and runny nose

a) Within 7 days of starting symptoms need an rRT-PCR (Real time Reverse Transcriptase - Polymerase Chain Reaction) test

b) After seven days - need an Antibody test and if this negative, an rRT-PCR test to confirm status.

How does the process work?

Any person who fits into these categories, needs to have a prescription from a medical doctor, signed by the doctor, with the doctor’s registration number and contact details (telephone and email ID). These are mandatory.

In addition, the patient must carry a copy of his/her Aadhar card when they come in for testing.

Once the patient arrives for testing, the test requisition form prepared by ICMR, needs to be filled.

The ambulant patient is then escorted to a dedicated area meant for collection of the Nasopharyngeal or Oropharyngeal swab samples. The swabs are collected by trained technologists who are protected with full Personal Protection Equipment (PPE). This process takes about 10 minutes and the entire stay in the lab takes about 20 minutes.

The collected swabs are immediately placed in bottles containing Viral Transport Medium, securely closed and labelled. They are packed in multiple layers and then transported to the lab at the earliest, at a temperature of 2-8 degrees C for further processing.

In very ill, hospitalised patients, other samples such as endo-tracheal aspirate or Broncho-alveolar lavage can be collected.

The test that can detect COVID-19 infections at the earliest, is the rRT-PCR. The SARS-CoV-2 virus being an RNA virus, initially it is extracted from the sample. It is then converted into complementary DNA (cDNA) using the enzyme reverse transcriptase (hence the name). This cDNA is then amplified using the PCR. By this amplification, even minuscule quantities of RNA in the original sample can be identified and a sample can be classified as either positive or negative.

On an average, a batch of about 50-60 samples takes 8-10 hours from the start of processing to completion. Reports are usually ready the following day as the tests are run in batches and in case a report needs to be confirmed it will need an additional day.

Rapid antibody screening tests will also be available soon, but need to be used judiciously and interpreted with caution. They are ideal for assessing the prevalence of infection in a population at a later date.

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