[BostonCard]

I think he's referring to a different Stanford study (note, it didn't measure antibodies, it was a PCR study of stored respiratory samples that were negative for other pathogens.

https://jamanetwork.com/journals/jama/fu...ultClick=1

They sampled ~3000 respiratory samples (nasopharyngeal and bronch) between Jan 1 and Feb 29, and found only two positive samples, both in the second to last week of February.

Obviously now we have at least one case that dates back to Feb 6 (and probably means she was infected in late January).

So how to reconcile the two sets of facts.  One possibility is sampling.  Stanford was collecting 300 - 500 samples a week during that period of time.  Getting zero positive tests would mean the confidence interval around the proportion is 0 to 0.9%.  Assuming the population reflects individuals in the Bay Area that display flu-like symptoms, it would be easy to envision a rate within that interval producing no positives in the study, but that still leaving many people out in the community, of which only one might have died.

Second possibility is that at the time it was a very localized cluster that wouldn't have normally gone to Stanford hospital for testing.  Same county, but there are a lot of hospitals in San Jose closer than Stanford, and if the cluster hadn't yet spread more widely, Stanford wouldn't see it.

The third possibility is that there is a methodological flaw in the Stanford study.  In order to cut down on their PCR kits, the Stanford researchers pooled samples together (and if any of the pools was positive, evaluated the individual samples).  If the pooling diluted the samples and decreased the sensitivity, it is possible that they would have missed cases.


Apparently California is relaxing restrictions for COVID testing, so if you do get serology, please do report your results (if you are ok doing so on a semi-anonymous forum).  Curious minds want to know!

BC

[BostonCard]

I think he's referring to a different Stanford study (note, it didn't measure antibodies, it was a PCR study of stored respiratory samples that were negative for other pathogens.

https://jamanetwork.com/journals/jama/fu...ultClick=1

They sampled ~3000 respiratory samples (nasopharyngeal and bronch) between Jan 1 and Feb 29, and found only two positive samples, both in the second to last week of February.

Obviously now we have at least one case that dates back to Feb 6 (and probably means she was infected in late January).

So how to reconcile the two sets of facts.  One possibility is sampling.  Stanford was collecting 300 - 500 samples a week during that period of time.  Getting zero positive tests would mean the confidence interval around the proportion is 0 to 0.9%.  Assuming the population reflects individuals in the Bay Area that display flu-like symptoms, it would be easy to envision a rate within that interval producing no positives in the study, but that still leaving many people out in the community, of which only one might have died.

Second possibility is that at the time it was a very localized cluster that wouldn't have normally gone to Stanford hospital for testing.  Same county, but there are a lot of hospitals in San Jose closer than Stanford, and if the cluster hadn't yet spread more widely, Stanford wouldn't see it.

The third possibility is that there is a methodological flaw in the Stanford study.  In order to cut down on their PCR kits, the Stanford researchers pooled samples together (and if any of the pools was positive, evaluated the individual samples).  If the pooling diluted the samples and decreased the sensitivity, it is possible that they would have missed cases.


Apparently California is relaxing restrictions for COVID testing, so if you do get serology, please do report your results (if you are ok doing so on a semi-anonymous forum).  Curious minds want to know!

BC