This tool to calculate risk of becoming infected w/ COVID19 is being promoted by some loud (& not well informed) folks. It gives ridiculously precise probabilities & data simply do not exist to quantify things this precisely.
Short thread
zeit.de/wissen/gesundh…
Tool allows you to adjust 1 or more: size of room, duration, # people, ventilation (4 levels!), masks (3 kinds!), speaking duration&volume. Online tool then gives prob of becoming infected & # infected through aerosols w/ precision (e.g. 21%, 2 people infected).
It then gives examples of risk calculation for 5 settings (classroom, restaurant, choir, office, living room). 4 shown here.
This tool is the worst kind of misinformation - it combines valid information w/ BS to provide an answer.
Real data:
-masks, ventilation, space decrease risk
-crowds, yelling, duration increase risk
It's absolutely silly to provide risks of becoming infected with extreme precision. As one single example, here's real data on masks showing huge variability in protection: 0->~50% in non-health care setting!

thelancet.com/journals/lance…
The tool also ignores most important aspect of risk: # of people in room - this DETERMINES probability that 1+ person will be infected/infectious! Tool assumes 1 person is infected & your chance of being infected doesn't change in room of 5 or 30!
It's accurate to say that settings where we can't wear masks are more dangerous than those where we can
It is also accurate to say we should ventilate rooms & bigger airspaces are safer.
Similarly, it's much higher risk if people are singing or talking loudly for a long time (which is partly why SCOTUS' recent decision blocking restrictions on church gatherings is so harmful).
It is NOT accurate to report a precise probability of being infected.
I hope this tool DOES encourage people to wear masks, open windows & avoid spending much time in small indoor settings w/ singing or loud talking.
But I hope people DO NOT think tool actually gives them accurate estimate of risk or adjustment for each option.

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More from @DiseaseEcology

3 Nov
Interesting new preprint trying to assess surface transmission of COVID-19/SARS-CoV-2.

tl;dr RNA is everywhere but in very low amounts; surface sampling could be useful for surveillance. Risk of infection unknown b/c study didn't look at live/infectious virus.
Short thread
Background
One of the huge early questions about transmission of SARS-CoV-2 was if the virus could be easily transmitted on surfaces. We all heard 1000s of times how much we should wash our hands, in part, to protect us against surface transmission. But...
Epidemiological evidence rarely suggested surface transmission was major issue. The best evidence for the absence of its importance (which is a hard thing to study!) was that (nearly?) all early cases in some locations (e.g. Singapore) could be traced back to known close contact.
Read 14 tweets
31 Oct
New paper showing very high household transmission of COVID-19 in US. I haven't seen detailed summary, so here's one. There's a ton here to think about. Kids, culture, COVID.
Thread.
cdc.gov/mmwr/volumes/6…
Background
Transmission of SARS-CoV-2 occurs primarily through sustained close contact. Certainly there are rarer more distant spreading events, but study after study shows that close contacts have an order of magnitude higher chances of becoming infected.
In case you want refs for this very well supported claim, here's a couple (& some data):
wwwnc.cdc.gov/eid/article/26…
thelancet.com/action/showPdf…
Read 24 tweets
29 Oct
How many SARS-CoV-2 infections are there per COVID-19 case now?
Early estimates & guesses suggested there were 10 infections for every case, but these estimates were done when testing capacity was very low. With higher testing capacity & better engagement where are we now?
Thread
Background
It's well known that confirmed COVID-19 cases are only a fraction of all infections. Infections can be missed because people are asymptomatic, have mild enough symptoms that they don't get tested, or can't get tested even if they want to due to accessibility.
In Mar-Apr underascertainment of infections was so large & uncertain it led to claims that there may have been hundreds of infections per confirmed case. A famous example is paper suggesting 1/2 of UK MAY have been infected by Mar
ft.com/content/5ff646… medrxiv.org/content/10.110…
Read 23 tweets
26 Oct
Very provocative new paper by @dylanhmorris @jlloydsmith on effects of temp & humidity on survival of SARS-CoV-2 on surfaces. Need to be careful in interpreting most novel aspects of this paper.
Thread.
Background
Effects of temperature & humidity on survival of viruses is potentially of huge importance as it can influence transmission b/w people & has been argued to be key mechanism driving flu seasonality. See perspective by @mlipsitch C Viboud pnas.org/content/106/10…
New paper suggests that viral survival on surfaces declines w/ temp & is lowest at intermediate humidity. If robust, could guide how to reduce risk of indoor transmission - warmer & 40-60% RH best. Indoor risk v important for next 4-6 mo. But... Image
Read 18 tweets
16 Oct
@CDCgov needs to harmonize/update all websites on spread of COVID-19
1 updated page has clear &(nearly) accurate information:
cdc.gov/coronavirus/20…
(here's detailed thread on update:
)
Many other CDC pages still focus on wrong mechanisms of spread
Thread
Updated page is clear about #1 mechanism of spread:
close (<6') contact
It also makes it clear that further >6' spread is possible
("airborne transmission") & when this occurs (indoors, poor ventilation)
Perhaps most importantly it accurately tells people how to be safe. Image
Relative ranking isn't completely right, but pretty good (still too much focus on surfaces, hand washing). For far more details on update see:
Read 11 tweets
10 Oct
How do we survive next 6-12 months?
Tweets by @TinaG_SD epitomize what many feel - even w/ relatively good measures in place, as in CA (mask mandate, bars/restaurants closed or nearly so, sick pay, etc.), transmission continues & cases ebb & flow & restrictions crush jobs.
Thread
COVID cases are surging in many parts of the US now where there are few measures in place (no mask mandates, open bars, etc.).

These measures certainly help but don't seem to be enough (see previous tweet). Why?
Transmission of COVID-19 is inherently a 2 step process. Step 1: Transmission w/in households is rapid with whole households sometimes getting infected.
Step 2: Transmission between households.
Read 17 tweets

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