Why Chances Of Getting A False Covid Report Have Increased

Multiple mutations in the coronavirus over the past 15 months are making parts of it unrecognisable to RT-PCR test kits

- Abhilash Gaur

It starts with a cough. Then comes fever and you feel short of breath. An alarm goes off in your mind. Is it Covid? You are so relieved when the test comes out negative, but four days later you are no better. A second test confirms Covid.

Many patients have experienced this in the second wave. As TOI reported on Tuesday, about 1 in 5 patients may get a false negative report. Sometimes, second and third tests also fail to spot the virus.

It’s worrying because the coronavirus is now fooling RT-PCR tests — the most reliable type. A false negative report is bad for the patient as they might delay consulting a doctor. It’s also bad for others, as the patient might not isolate, and spread the virus around.

Why are tests failing? It’s because the virus they were designed to detect has changed its look and behaviour considerably since last year. It’s like you lost a puppy a year ago and are still trying to trace it with old photographs.

Tests based on old virus

A research paper by University of Illinois and Michigan State University scientists had raised this concern last September: “PCR diagnostic test reagents were designed based on early clinical specimens containing a full spectrum of SARS-CoV-2, particularly the reference genome collected on January 5, 2020, in Wuhan.”