I wrote in a previous post about Koch’s postulates. To recap, whether you get an infection or not, depends on 3 things:
1. Host vulnerability – if you are immunocompromised (for example)
2. Virulence of the organism – if you get Ebola as opposed to a mild cold
3. Dose of organism – if you have a huge dose of an innocuous infective organism you are more likely to become ill than if it is only 1 bacterium or virus.
With the Corona virus we know that certain individuals are more prone to both catch the disease and to die from it. We do know that people of BAME groups are more likely to be affected and so are front line NHS workers. There is much consternation over this, but applying the above, there may be some answers. It is improbable that it is postulate 1 or 2 above that results in the increased incidence and death rate, although clearly older individuals are more likely to die if they get the respiratory distress and since they have more ACE 2 receptors, they will get a bigger viral load.
Since front line workers are not only more likely to get the virus and more likely to die from it, it seems logical to assume that the problem is dose of virus. They are exposed to far more virus than the average person out for a walk 2 meters away. The droplets hang around in the air in a still atmosphere for hours so exposure to that environment makes it more likely that the dose of virus is high where the PPE mask (for example) didn’t fit properly or the virus gets in through the eyes under the visor.
The much-maligned Marseilles study showed that in people who were mildly infected, they cleared the virus quickly and it was assumed to be the drugs responsible. I make no judgement on that, but I suspect the real significance was that the ones who went on to develop the late respiratory distress syndrome probably had such large doses of virus that they overloaded their immune system and developed the auto-immune ARDS.
There are numerous studies which show that using acoustic rhinometry, the size of the nasal cavity varies with ethnicity and that Caucasians have smaller nasal cavities than other racial groups. Asian people are in-between in nasal cavity size. The proportionate difference is very similar to the racial differential mortality with Covid-19. I think this may be important because in a large nasal cavity, the infection will cause a greater viral load, leading to a greater likelihood of the late development of the respiratory distress and organ failure.
All this leads me to conclude that the size of the viral load is the important factor in the development of the severe acute respiratory distress. The people with mild illness had a smaller dose and cleared the virus quicker.
Just sayin’ is all.