[BostonCard]

When the virus started to spread in Guangdong — the province where the 2002-2003 SARS outbreak began — worried people flooded fever clinics to be tested. Of 320,000 tests performed, just under 0.5% were positive for the virus at the peak of transmission there, he said — which suggests that only 1 case out of 200 was being missed.

Again I'll point out that the Chinese National Health Council guidance (in my link earlier) for wearing face masks was for HEALTHY individuals that were going to be where they might be exposed to illness (people in crowded places, indoor working environment, ...).    If they were sick, at least with this disease, they weren't out walking around!

Indeed, the WHO-China Joint Mission reported that (apparently in Hubei), as part of the controls, "Every citizen has to wear a mask in public."

That doesn't make sense or at least the phrasing is misleading.  If the 320,000 people tested were representative and .5% were positive, it doesn't mean that 1 in 200 cases are missed, it means that 1 in 200 people have an undetected case.  The population of Guandong is 113.46 million, so if .5% are positive, that's 56500 undetected cases.  Since there are 1350 cases in the province, that means that >97% of cases are undetected.

If you just focus on the subgroup of patients with fever, the calculation is much more difficult.  You would need to know the incidence of fever.  And the results of Guangdong at a particular point in time can't be extrapolated to other places or other timepoints where the underlying prevalence of Covid-19 (not to mention other causes of fever like flu or run of the mill pneumonia).

The bottom line is I wouldn't extrapolate.

As for the mask, really the best you can hope for is that if someone has a mild illness, and doesn't know they have mild infection, and still insist on going out of the house, the mask might protect others.  I think the biggest value is in signaling.  We must do something to stem the pandemic.  Requiring masks is something.  Thus we must require masks.  It's like security theater but for pandemics.

BC

[BostonCard]

When the virus started to spread in Guangdong — the province where the 2002-2003 SARS outbreak began — worried people flooded fever clinics to be tested. Of 320,000 tests performed, just under 0.5% were positive for the virus at the peak of transmission there, he said — which suggests that only 1 case out of 200 was being missed.

Again I'll point out that the Chinese National Health Council guidance (in my link earlier) for wearing face masks was for HEALTHY individuals that were going to be where they might be exposed to illness (people in crowded places, indoor working environment, ...).    If they were sick, at least with this disease, they weren't out walking around!

Indeed, the WHO-China Joint Mission reported that (apparently in Hubei), as part of the controls, "Every citizen has to wear a mask in public."

That doesn't make sense or at least the phrasing is misleading.  If the 320,000 people tested were representative and .5% were positive, it doesn't mean that 1 in 200 cases are missed, it means that 1 in 200 people have an undetected case.  The population of Guandong is 113.46 million, so if .5% are positive, that's 56500 undetected cases.  Since there are 1350 cases in the province, that means that >97% of cases are undetected.

If you just focus on the subgroup of patients with fever, the calculation is much more difficult.  You would need to know the incidence of fever.  And the results of Guangdong at a particular point in time can't be extrapolated to other places or other timepoints where the underlying prevalence of Covid-19 (not to mention other causes of fever like flu or run of the mill pneumonia).

The bottom line is I wouldn't extrapolate.

As for the mask, really the best you can hope for is that if someone has a mild illness, and doesn't know they have mild infection, and still insist on going out of the house, the mask might protect others.  I think the biggest value is in signaling.  We must do something to stem the pandemic.  Requiring masks is something.  Thus we must require masks.  It's like security theater but for pandemics.

BC