Just a reminder that we have two-fifths of FA real data on how any single person or group gets infected by SARS-CoV-2.
We're not there to observe the process. We mostly can't exclude surface or droplet or aerosol. We can apply what we expect to have happened.
But remember...
...we do that using our current settings with all their glorious biases. Some of the knowledge that came before has evidence that's a degree removed - we know SARS-CoV-2 survives in aerosols & can infect primates; but we haven't infected a human that way.
We know droplets are emitted when we cough, yell & sing & not when we breathe or talk normally. But aerosols are always emitted so how do you know droplets were in play & not time (dose) of aerosol exposure if you're proposing close-up infection was only by droplets? You can't.
We know virus survives on nice clean surfaces (sometimes in the dark & in ideal conditions & big doses) but we don't know how it lasts on surfaces in the real dusty, greasy, sunny, windy, oft-contacted world.
We also know that virus-contaminated fingers can spread virus that can be recovered from light switches and other surfaces & fomites thanks to work even from decades ago. But we can't point with absolute assurance to any person having been infected that way by SARS-CoV-2.
We know SARS-CoV-2 infects in a chunky way - not every person infects 2or 3 others, some infect none, some infect many. This "overdispersion" can't always be explained by proximity or shared surfaces, but aerosols fit. Sometimes it isn't that way & multiple routes are in play.
So embrace the uncertainty here folks!
And while you see scientists picking faults in what looks like any scientific paper from anywhere, make sure you ask them to tell you where the better data are as well. Or, if there are no better data, then that's also important to know

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More from @MackayIM

25 Nov
In the spirit of filling those with no PCR experience in. This is a lunchtime thread showing the progress of a reverse transcription polymerase chain reaction (RT-rPCR) "run".
The thing being amplified-the target or template-is a tiny amount of RNA I'd previously made
...in the lab ("in vitro transcribed RNA").
At this point there's too small an amount of RNA to view or use to get specific virus info from, so we put it through some chemistry & cycling temperature changes (the RT-PCR process) to copy it to levels we can "see".
RT-PCR isn't the only way to do this but its the topic here
So after the ivtRNA is added to a tiny tube (0.2ml) with enzyme, buffer, water, 2 primers and a probe, it's incubated at 50'C for a few minutes for RT enzyme to copy the RNA into complementary DNA (cDNA).
No signal yet
Read 24 tweets
20 Nov
I think these graphs from @NSWHealth are both beautiful and really interesting.
Look at that RSV take off. This will be impact young kids and those with asthma I'd expect. But it's a *very* late season. Highlights that "seasonal respiratory viruses" are about more than "season"
RSV and RV peaks don;t line up - but RSV lags RV. Here's one hypothesis (lest call it the RV as MASTER hypothesis)- RVs wane - for whatever reason, lots of immunity - RSV able to get a foothold and takes off.
Or RSV as MASTER, hypothesis: huge cohort of immune naive kids for RSV to take hold in, pushes out RVs (lag due to this happening in the background, not being captured by testing for some reason)
Read 4 tweets
20 Nov
Parafield, South Aust #COVID19 Media Update 20NOV2020
🎙️14,400 tests in past 24h
🎙️Restrictions to be rolled back but circuit breaker was needed
🎙️Contact tracers show person linked to pizza bar misled the team ("they lied")-new group being sought
🎙️SA public urged to get tested
🎙️Outside exercise permitted for those you live with or family groups, immediately
🎙️Stay at home order being repealed from midnight Sat, replaced by density rules (1/4m2 in premises; 100 in hospitality premises, 10/table; funeral-50, weddings 150)
🎙️Masks required for personal care provider
🎙️Gyms to reopen from midnight Saturday
🎙️Schools back from Monday
🎙️#PizzaLie=the person was working there for several shifts, not just purchased a pizza from there (no lockdown if they'd been honest!😬)
Read 9 tweets
18 Nov
"the trial did not test the role of masks in source control"
-which is a key role for masks in reducing transmission *from* and infected 'source', to others
acpjournals.org/doi/10.7326/M2…
But, you know, it had some acknowledged overall issues.
"Inconclusive results, missing data, variable adherence, patient-reported findings on home tests, no blinding, and no assessment of whether masks could decrease disease transmission from mask wearers to others."
-there doesn't seem to have been a baseline PCR test (would have been nice, but not essential except to catch ? Image
Read 4 tweets
17 Nov
I wonder if we'll ever really discuss eye protection for the public?
Pros/Cons.
Useful? Over-the-top?
So many things still have so little actual evidence to makes these calls.
An yet you see images like this...
Ugh.
Coincidentally...
Prevalence of SARS-CoV-2 in human post-mortem ocular tissues sciencedirect.com/science/articl…
Small studies have rarely found (old links):
😷SARS-CoV-2 RNA in tears & conjunctival secretion in 1 of 30 COVID-19 cases
doi.org/10.1002/jmv.25…
😷2 of 72 COVID-19 cases with conjunctivitis had viral RNA detected in a conjunctival swab
medrxiv.org/content/10.110…
Read 5 tweets
16 Nov
Where is South Australia, I hear you ask (hopefully I hear no Aussies ask that!)
A couple of amateur but curmudgeonly Comms thoughts
🦠Parafield cluster - the name of this #COVID19 event in #SouthAustralia.
sahealth.sa.gov.au/wps/wcm/connec…
🌊This isn't Wave 2 for SA-it's a cluster. And talking about it as if it is the start of Wave 2 may induce fear rather than caution and risk reduction activities.
Qld dealt with a cluster recently without statewide lockdown. Can be done.
Read 6 tweets

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