Interesting study from Vietnam.
“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…
“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…
14,000 tested for SARS-CoV-2
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?).
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?).
THey don’t put error bars on the asymptotic fraction.
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!
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!
Odd that they only managed to recruit 30 of the 47 positives into their study.
Most of those had travelled outside the country (what about the others one wonders?).
An opportunity for (self-)selection bias?
Most of those had travelled outside the country (what about the others one wonders?).
An opportunity for (self-)selection bias?
They measured viral RNA not live virus (shame but the latter is difficult if more valuable).
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?
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?
Recall the German and Singaporean work that shows no live virus after 7-9d in mild cases.
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?
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?
Interesting longitudinal plots of viral RNA Ct count.
Note Dosten’s found that for Ct > 24 case has no live virus.
Most people don’t have live virus after the couple of days at most but some have a spike at 5-7d.
Either that’s real (going for the LRT?) or a weird artifact.
Note Dosten’s found that for Ct > 24 case has no live virus.
Most people don’t have live virus after the couple of days at most but some have a spike at 5-7d.
Either that’s real (going for the LRT?) or a weird artifact.
Those days are “After enrollment” so perhaps “after infection + n”
But we have no idea what n is.
But we have no idea what n is.
So if the viral RNA copy count matches the live virus load in the throat for the first week then asymptomatics have
But the individual Ct counts seem to show Ct > 24 for a lot of these patients.
Do they have even less virus? Nice to see a regression that thresholded at 24.
But the individual Ct counts seem to show Ct > 24 for a lot of these patients.
Do they have even less virus? Nice to see a regression that thresholded at 24.
So what are my conclusions from the Vietnamese asymptomatic study from this reading:
1. Asymptomatics are probably < 50% of cases.
2. Asymptomatics are less infectious (possibly much less infectious, more than the paper says) than (pre)symptomatics.
1. Asymptomatics are probably < 50% of cases.
2. Asymptomatics are less infectious (possibly much less infectious, more than the paper says) than (pre)symptomatics.
What is with patient 21? Asymptomatic with Ct > 40 for all tests
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%.
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%.
