Thread: very useful new systematic review & meta analysis: 1/n

One caveat re: duration of infectiousness is that the cell culture studies almost exclusively looked at naso/oropharyngeal specimens. 2/n
The question is, is cell culture of naso/oropharyngeal specimens an adequate surrogate measure for infectiousness? 3/n
Some studies have shown that viral loads may be higher and slower to decline in sputum, suggesting greater and potentially more prolonged infectiousness: 4/n

nature.com/articles/s4146… Image
Only one study referenced in the Lancet Microbe SR&MA attempted to culture sputum from a cohort of 16 patients with mild disease: 5/n

nature.com/articles/s4158…
A greater proportion of sputum samples yielded positive cultures as compared with swabs, but no cultures from any location were positive beyond day 8: 6/n Image
And all positive cultures had high viral loads: 7/n

(orange=sputum, yellow=swab, grey=stool). Image
However, there were only 5 sputum cultures performed on samples beyond day 8 from an unclear number of patients (though there are 16 orange dots, so probably 5): 8/n

(orange=sputum, yellow=swab, grey=stool). Image
And the study included only 2 patients who showed signs of lung infection, in whom:

“sputum viral loads showed a late and high peak around day 10 or 11, whereas sputum viral loads were on the decline by this time in all other patients.”

When they were cultured isn't clear. 9/n
A <5% isolation success from cell culture was predicted >9.78 days or <5.4 log10 (~250k) RNA copies/mL, but 95% confidence intervals were wide: 10/n Image
Whether these small numbers of patients and sputum cell cultures beyond day 8 are representative is unclear and I’m not sure we can be confident about the tail end of the infectious period based on the information currently available from cell culture studies. 11/n
On the other hand, the authors of the Lancet Microbe SR&MA reference two contact tracing studies that also point to early transmission, one of which addresses the tail of the infectious period: 12/n
100 index cases in Taiwan led to 22 secondary cases/2761 contacts; no cases were identified in contacts whose exposure started more than 5 days following symptom onset in the index case (0/852 contacts). 13/n

jamanetwork.com/journals/jamai…
Pretty reassuring, but still a relatively small number of index cases and transmission events.

Anyone know of any meta analyses of contact tracing studies looking at the infectious period? 14/14 - end.

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Devon McDonald

Devon McDonald Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @McDevonMD

28 Jun 20
I wish I had a bigger follow to promote this paper because I think this kind of research is so important. I just joined twitter, so I don't, but I'll try to do my part anyway. Have a look at: medrxiv.org/content/10.110…
They found that HCWs were identified as cases of COVID at a rate 5.5x nonHCWs (range 2-6 mirroring the epidemic curve), and that 9.8% of HCWs likely transmitted to a household contact. Lots of other stuff in here but these were the findings I found most interesting.
I don't think the available data allowed them to adjust for a differential rate of testing, which was almost certainly higher among HCWs, though I doubt 5.5x higher. On the other hand, the denominator used to calculate rates of identified cases in HCWs was probably over-inclusive
Read 11 tweets

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal Become our Patreon

Thank you for your support!

Follow Us on Twitter!