Compiled by Dr. Narendra Malhotra
Corona is here to stay and it is predicted that over 70% of population will get the infection (fortunately not all will fall sick or very sick). (Recovery rate of over 74% & Death rate around 2%).
A lot of confusion exists regarding testing for covid and what test to do, when and how to interpret these tests.
For any disease the attack virus or the contagion is called “ANTIGEN” and when this “antigen” enters our body, our body defenses (known as ANTIBODIES) try and kills the contagion. Our body has general antibodies present which are known as our “IMMUNITY”.
If the general antibodies are not able to kill the ANTIGEN or it’s a new antigen our body defense mechanism is activated and our body produces specific ANTIBODY IgM & IgG and Cytokines against the attacking CONTAGION. This takes some time (7 days for IgM) and then 14 days for IgG. These antibodies remain in plasma and prevent further attack by that CONTAGION. These antibodies last from some months to years & some cases forever. This is how vaccines work. In a vaccine there is a dead or inactive (Live attenuated contagion) which is injected and this produces antibodies against that disease. Vaccination has eradicated small pox and polio and has saved many children from TB, Mumps, Rubella, Measles, Rota virus, Encephalitis, Hepatitis, Chicken pox (There are some the diseases against which a vaccine is available).
Very soon we will have a vaccine against CORONA (SARS-COV-2/ COVID 19) like we have for influenza (H1N1 flu – INFLUVAC-TETRA vaccine).
CORONA Tests- lets understand corona infection (ANTIGEN & ANTIBODY)(Fig 1)
Following tests are available for Corona virus detection (Antigen & Antibody) The sample for Corona virus test can be taken as-
a. Swab Test (from nose & throat)
b. Nasal aspirate (saline solution in nose & suction)
c. Tracheal aspirate – by bronchoscope from inside lungs
d. Sputum test – cough out sputum from lungs
e. Blood test – venous blood
f. New – from saliva (still experimental stage)
These samples can be tested for the presence of virus RNA(Antigen) (contagion) and from blood we can also test for presence of Antibody.
a. Viral – Antigen Test – This test tells if person is suffering from current infection. Positive report indicates Corona infection negative report signifies person is not infected at time of testing.
High specificity but limited sensitivity especially by Rapid antigen test. (Fig 2)
b. Antibody test (IgG evaluation) tells us Total Antibody. Test is possible and should be more than the normal value which indicates that the person has had antigen. In persons if CPR & ESR are not increased, increase the immunity is developed less. (Antibody develop less if infection is mild)(Fig 2).
c. Other tests for severity of infection and for monitoring the disease(Fig 3).
To test in the community we can do a community RTPCR test in groups of asymptomatic cohorts to pick up corona infection. If cohort test comes positive, then all are tested.
Also in community serosenstivity testing (Antibody Test) can be applied to pickup herd immunity in community.
We hope we have clarified a few facts about tests which are available and what the indication for which test.
Until we have an effective vaccine to be used for masses, kindly take simple precautions of sanitizing – masks – social distancing.
Be Safe !
Further reading guidelines of WHO, CDC, FDA, ICMR, IMA & FOGSI Brought to you for public awareness by Rotary Club Agra Taj City.