And of course defining pre-symptomatic is a little bit tricky because often times people have very slight prodromal symptoms before they become febrile and develop significant cough .
This is exactly what I think is going on. People vary in the constellation and progression of symptoms but some will be something like this:
1. Runny nose, 'sinus' complaints, 'allergy' complaints and sneezing; then
2. Scratchy throat, occasional cough; then
3. More prominent cough; then
4. Fever and malaise; then
5. Pleurisy or progressive dyspnea
When is a person first symptomatic ? A physician will say (1), but depending on how careful the history is obtained (2), (3) or (4) may be reported.
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Somewhat tangentially, the NYT has an interesting report on the success of Taiwan in containing Covid-19. Two of the pillars of infection detection were fever (4) and self reporting of symptoms and high risk contacts. I wonder if the Taiwanese are just much better educated and self report from (1) or other factors are in play. Their success is certainly indirect evidence that the math model is wrong.
The most basic problem with the 'asymptomatic and infectious' notion is that it goes against a century of understanding viral respiratory disease epidemiology and pathophysiology. Symptoms are indicative of significant cytopathic effect, itself indicative of viral load. Spread is via cough and sneezing; and to a lesser degree rhinitis, all symptoms of infection.