06-22-2020, 02:26 PM
Exactly.
Remember, the R0 of the virus is estimated at between 2 and 3, so absent any intervention, on average each infected person will infect 2 to 3 susceptible people. If R is > 1, the epidemic will increase exponentially; if R < 1 the epidemic will decrease and peter out. Because of social distancing, right now R is somewhere in the 1 to 1.5 range in the US. That means that cases are growing, slowly. In order to "win" you don't have to stop all remaining infections; you just have to stop enough of them to get drive R to below 1.
So, let's say that on average 50% of patients are symptomatic. You find a symptomatic patient, and trace both forwards and backwards. If you alert and test most of that person's contacts, you should be able to catch all the symptomatic patients early (since now they are primed to look for symptoms and assume that their mild cough is actually COVID-19 and not their allergies), and you might catch the asymptomatic patients if you test them at the right time. Even if you don't catch their asymptomatic contact, by telling them they've been exposed and to quarantine, even if it is not perfect, you can probably reduce their close personal contacts by 50%, enough to drive R to below 1. You also trace backwards, and hopefully identify the person who infected them, who should test positive (symptomatic or not). That will let you test all that patient's contacts.
Yes, the system won't be perfect. But it doesn't have to be perfect as long as 1) there are reasonable measures to reduce transmission (social distancing protocols, mask wearing, etc.) and 2) you interrupt enough chains of transmission to drive R to below 1. If you do all that, infections will go down over time (which incidentally makes your job easier).
BC
Remember, the R0 of the virus is estimated at between 2 and 3, so absent any intervention, on average each infected person will infect 2 to 3 susceptible people. If R is > 1, the epidemic will increase exponentially; if R < 1 the epidemic will decrease and peter out. Because of social distancing, right now R is somewhere in the 1 to 1.5 range in the US. That means that cases are growing, slowly. In order to "win" you don't have to stop all remaining infections; you just have to stop enough of them to get drive R to below 1.
So, let's say that on average 50% of patients are symptomatic. You find a symptomatic patient, and trace both forwards and backwards. If you alert and test most of that person's contacts, you should be able to catch all the symptomatic patients early (since now they are primed to look for symptoms and assume that their mild cough is actually COVID-19 and not their allergies), and you might catch the asymptomatic patients if you test them at the right time. Even if you don't catch their asymptomatic contact, by telling them they've been exposed and to quarantine, even if it is not perfect, you can probably reduce their close personal contacts by 50%, enough to drive R to below 1. You also trace backwards, and hopefully identify the person who infected them, who should test positive (symptomatic or not). That will let you test all that patient's contacts.
Yes, the system won't be perfect. But it doesn't have to be perfect as long as 1) there are reasonable measures to reduce transmission (social distancing protocols, mask wearing, etc.) and 2) you interrupt enough chains of transmission to drive R to below 1. If you do all that, infections will go down over time (which incidentally makes your job easier).
BC