A simple infographic comparing Covid-19 Tests
https://www.covid-gyan.in/infographic/comparison-covid-19-tests
A close look at the commonly used COVID-19 tests by Meena Kharatmal (HBCSE, TIFR).
I take this opportunity to acknowledge the coordination with IISc team member, guidance of TIFR team members, support from HBCSE in this effort.
Its been a good opportunity and learning experience.
Very nice.
Why is the RAT only indicative of past infection? Won’t it show up on anyone whose body is naturally immune?
A different question: what kind of scan might be capable of identifying the particular antibodies* without drawing blood? Are there any organs (like, for instance, the eyeballs) where blood is sufficiently visible that a particular very small wavelength reflection might positively identify singular antibodies?
Such a test might then be generalised in nature, allowing ordinary people to be instantly scanned for any kind of infection that normally produces antibodies (whether or not an epidemic is already in progress), thus building up an immunity profile.
Well the rapid antibody test is indicative of past infection due to the specific type of antibody – IgM – that is produced as a natural immune response in the blood, just at the onset of infection. These are the first type of antibodies produced by the bodies, and are expressed without class switiching.
IgG antibodies are most common antibodies covering upto 75% - 80% of all antibodies in our body. These are produced within 7 seven days after the infection. Therefore it detects past infection.
These two are specific antibodies that are produced by fighting bacterial and viral infections in the blood. While other types of antibodies such as IgE, IgD, IgA, are seen to be found in various fluid or mucus membranes of various organs such lungs, etc. Some are found in ear nose eyes throat saliva tears etc. as well. These are specific to produce while defending allergies or fight from foriegn substances such a pollen, fungus etc.
So the antibodies of interests that are produced as a result of fighting viral infection – IgM, IgG- produced in blood and hence the blood test. Also its safe and quick and cost effective.
As far as your other point about detecting antibody without any intervention tests, I am thinking widely… perhaps just like the temperature detector device, it needs to detect at the molecular level, to check the specific arrangement of molecules etc. I am not sure at this moment about this. Now that you raised such intriguing point, I did a quick read and figure out some devices using LED, laser etc. but using blood drop. So a drop of blood is still required to be drawn for the study.
A species of african rat can detect tuberculosis with extremely high accuracy.
The UK is currently studying the use of trained dogs to detect the odour — from clothing — of a coronavirus asymptomatic case. The expectation is that this non-invasive method will rapidly screen, at 250 persons per hour (per dog, but dogs do get tired, it’s not magic) at barrier locations such as trains and airplanes.
Perhaps India can investigate whether cows can do a similar job. The great advantage is that nobody will beef about false positives, and the authorities will blindly overlook all possibilities of false negatives.
Anyhow, to return to remote testing, yes, a scan must analyse at the molecular level. It can’t be analogous to gas chromatography, though, as that will mainly (only?) detect elements, not compounds, apart from the thought of vapourising blood in the eyeball being a little intimidating. Perhaps some form of crystallography?
Yes, that is my point, that the infection is being fought, it need not be a patient who is fully cured. While the death rate is fortunately low, those are people who are probably don’t have the right immune systems: however, the percentage of people who don’t need advanced care is also low, so it ought to be easy to obtain reference samples of the right antibodies, that can be used in a non-invasive non-destructive test kit.
Interesting discussions @vvcstemplay @jtd. Now that sniffing the biomarkers of volatile organic compounds by dogs is being studied. Then how about a device like a breath analyzer for non-invasive testing. It works for testing drunk driving 
here is a latest paper in related work : Review—Non-Invasive Monitoring of Human Health by Exhaled Breath Analysis: A Comprehensive Review - IOPscience
Regarding …
I am wondering if this case can be resolved through acquired herd immunity in the population over a period of time.
sahi pakde hai … nice play on words…
Despite the percentages being low, the numbers are humongous given the size of our populace. India is likely to have far far more casualties given the abysmal medicare even at the best of times.
Excellent idea! I was thinking, this is not restricted to Covid-19, it is a suggestion for a generalised test that can help identify people with lower natural immunity, at almost no cost. That way, vaccines will be necessary for a much smaller number of people, and developed for the really critical illnesses such as hemorrhagic fevers and so on that today have no cure.
Well, almost no cost meaning that we have to think about the capital cost of such hardware. Are test kits (for reference) necessary, or can a digital database serve the purpose? Either way, both are simple to update and widen, over time, although the former will be more expensive, given the nature of consumables.
In the old way of doing things, no business would invest in such a market-unfriendly technology. But even a cursory reading reveals that all across the world, serious thought is now being given to technologies that are less resource-intensive/wasteful, and ways of doing business around such technologies, such that people can live with economic systems that do not depend on continuous growth without regard for cost to the planet on which we live.
@vvcstemplay. A symptom in asymptomatic patients and probably identifiable by non contact means .
Marvi Cheema et al, Keratoconjunctivitis as the initial medical presentation of the novel coronavirus disease 2019 (COVID-19), Canadian Journal of Ophthalmology (2020). DOI: 10.1016/j.jcjo.2020.03.003
http://dx.doi.org/10.1016/j.jcjo.2020.03.003