“Asymptomatic SARS-CoV-2 infection is common [43%] and can be detected by analysis of saliva or NTS. NTS viral loads fall faster in asymptomatic individuals, but they appear able to transmit the virus to others.” academic.oup.com/cid/advance-ar…
49 were positive.
But only 30 participated in the study (chance for selection bias?)
13 (43%) never had symptoms and 17(57%) were symptomatic.
17 (57%) participants acquired their infection outside Vietnam (travels more likley to be selected?).
An estimate for the standard deviation of the asymptomatic result (from Poisson stats) is 30% to 55% (and even wider than that if you want 95% CI 20%-65%).
Interesting but it doesn’t nail it down!
Most of those had travelled outside the country (what about the others one wonders?).
An opportunity for (self-)selection bias?
And they measured it late in the progress of the disease at 19d.
Does the shedding of viral RNA 19 days after onset have a correlation with shedding live virus in the first week?
So
“Both asymptomatic and symptomatic patients had the same probability of RT-PCR positivity after the first week of follow up”
Is there really a difference in load here?
But we have no idea what n is.
1. Asymptomatics are probably < 50% of cases.
2. Asymptomatics are less infectious (possibly much less infectious, more than the paper says) than (pre)symptomatics.
So tested positive once then nothing. False positive in PCR?
Patient 25 iall but one test (at Ct ~37) at Ct > 40
Patient 28 only one test at Ct ~ 35
Ignoring these (should we?) would drop asymptomatics to 30%.