Covid testing and viral load

From my personal experience

At railway hospital, bhubaneswar

RTPCR is a multiplier test. A state of the art machine multiplies the nucleic acid present in your nasal sample till it detects the virus.

The number of cycles ( of multiplication) it takes before detecting the virus is called the Cycle Threshold. ( CT value)

The higher the CT value ( say > 25) the lesser is the viral load, less chance of Contagion.

It’s a time consuming ( 6-12 hours) and technology intensive procedure. The viral sample must be transported all the way to the lab in a biosafe manner, in a cold chain and in good condition also.

Advantage:

It can detect tiny quantity of virus in a mixed sample. Hence it is taken as the Gold standard.

What is the chance of missing ?

It’s possible, but chances are miniscule. Though there always will be some human error.

There is actually no false positive in the test process. However, Sample contamination at the time of collection or during transportation or any labeling error should be excluded.

Antigen Test ( RAT):

It is also known as the Rapid Antigen Test as it takes less than 30 minutes.

A sensor against the viral antigen is incorporated into a cartridge. When a drop of nasal sample is added to it, a positive line appears in 20 minutes.
( pic)

Advantage:

It is portable, requires no special skill, and is a very good bed side test.
..
As there is no multiplication of viral material in the process, it will miss a patient when the viral load is very less. False Negative.

But once positive, it says the viral load in the sample is pretty good.

There is no false positive. because contamination chance is very less.
We have not encountered a single false positive in RAT in our hospital till date.

Discussion:

Viral load decides infectivity.
The higher the load, the greater the chance of contagiousness.
We must isolate those infective patients in a mixed gathering.

In fact, some of the most serious covid patients are non infective. ( Covid virus per se is not dangerous. It is our body’s over reaction to the virus – the cytokine storm causes us damage.)

Conclusion:

RAT is the test of choice for the control of epidemic. It can be used to screen out the infective patients before any emergency procedures.

What about antibody tests ?

Truth be told, an antibody test if positive only indicates that you have an exposure to the virus in the first 2-6 weeks. Present status not known.

It doesn’t certify that you won’t have the infection again. This virus being a coronavirus is likely to mutate in future and your present antibodies can’t stop it from infecting you second time in 2021.

That also applies to all the first generation vaccines. No guarantee that they will match the virus circulating in 2021.

( I don’t have any experience about the CRISPR test till date.)