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Coronavirus Covid-19 (Read 681173 times)

petejh

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#1100 Re: Coronavirus Covid-19
March 26, 2020, 01:46:06 pm
Yes that's the theory going round. Supposedly related to 'Cytokine release syndrome' (layman caveat applies). 
But isn't it well established that there's a lower probability of reaching that point in the stage of illness, from one microbe of a virus entering your system then one thousand?
(numbers obvs just for illustration, magnitudes higher in reality) 

Will Hunt

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#1101 Re: Coronavirus Covid-19
March 26, 2020, 01:46:43 pm
If you have a high viral load you are more likely to infect others seriously when coughing etc

That bit in bold there is the bit that you've assumed. People with higher viral loads are more infectious, and they tend be more unwell. But you haven't shown any evidence to suggest that a greater infectious dose would lead to a more severe illness.


Pete, I think you're right that other viruses (like flu and SARS type viruses) do show this behaviour. But I don't think it's yet been demonstrated in COVID-19 (or rather, I haven't seen it demonstrated). There is evidence (from mice I think) that lots of low-level exposures can infect just as well as a single high infectious dose, but again, I haven't seen evidence that shows that this then leads to more or less severe illness.

I think Offwidth is probably correct in his assumption, but it irks me that it's made with such authority when it is actually just an assumption (albeit one that is quite probably correct).
The way that I conceptualise the disease, it seems obvious that a greater infectious dose would lead to more severe illness - you could say you're giving it a head start. But I'm not a virologist or an immunologist, so I don't know whether (let's say) a higher infectious dose would trigger a greater response from the body's immune system, which cancels out the higher initial dose. It could be that higher infectious doses lead to more severe illness, but that the effect is generally not significant. What would a graph look like if you plotted infectious dose on the x and disease severity on the y? Would it be a straight line climbing up? Would it be a steep line? Or would it a curve? At what rate would the curve steepen? What is the critical infectious dose that we should be wary of - a cough in the face from someone on an intensive care bed, or using a mucky door handle followed by picking your nose?

This is a really critical thing to understand because it has an impact on how careful we need to be when out and about, and about how we might need to isolate in our own homes to protect our families. My suspicion is that Offwidth is jumping to conclusions because it gives a good opportunity to get cross at the government. As I say, he's probably right, but I wouldn't mind being shown the science behind it so that we can actually understand it fully.

Ru

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#1102 Re: Coronavirus Covid-19
March 26, 2020, 01:52:39 pm
Will's point is correct.

We know that those that are more seriously ill have a higher viral load (more of it in their body) and are therefore more likely to infect others (as more of it expelled into the air/onto surfaces).

What seems to be conjecture is that the seriousness of the resulting illness in the person that catches it is dependant on the strength of the initial dose. Clearly this makes intuitive sense in that the immune system may find it easier to fight off a lower initial dose, and it accords with anecdotal experience of lots of doctors being seriously ill, but I've not seen any evidence for it.


Will Hunt

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#1103 Re: Coronavirus Covid-19
March 26, 2020, 01:54:36 pm
And when I say that "we" don't understand it, I'm referring to the amateur medics who are posting on this thread like we're some sort of WHO critical research team  :) :lol:

petejh

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#1104 Re: Coronavirus Covid-19
March 26, 2020, 01:59:43 pm
Good points.


My suspicion is that Offwidth is jumping to conclusions because it gives a good opportunity to get cross at the government. As I say, he's probably right, but I wouldn't mind being shown the science behind it so that we can actually understand it fully.

 :)
I read the majority Offwidth's posts as if in brackets:
[I am angry at this government and all I see, do and say is tainted by this bias]
Offwidth's comment.
[/I am angry at this government al everything I see, do and say is tainted by this bias]


I think the forum would benefit from this option and some others..

mrjonathanr

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#1105 Re: Coronavirus Covid-19
March 26, 2020, 02:05:59 pm
Clearly this makes intuitive sense in that the immune system may find it easier to fight off a lower initial dose, and it accords with anecdotal experience of lots of doctors being seriously ill, but I've not seen any evidence for it.

We are all making lots of assumptions. It seems simplistic to me that a single numerical input determines severity of illness. I'm unconvinced it makes much difference to outcomes whether you ingest a single virus picked up from a dirty touch screen vs being coughed over by a very unwell person- once. Surely doctors are repeatedly exposed to high numbers of virus cells, hour after hour, day after day- and it is that which impacts the body's ability to cope?

tomtom

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#1106 Re: Coronavirus Covid-19
March 26, 2020, 02:25:34 pm
Ru: health workers in China and esp now in Spain have far higher rates of hospitalisation wjenCb19 positive than the general population. This is well documented.

Whilst that doesn’t mean that viral load or repeat exposure (to more viral load) is the cause - it’s hard to explain in any other way. Cause and effect,  Black swan/white swan etc.. etc.. 

Interestingly - this and the key issue of shortage of health workers due to illness and the need to protect them was one of the key points by the virologist charting in a podcast linked in the first few pages of this thread.

petejh

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#1107 Re: Coronavirus Covid-19
March 26, 2020, 03:31:33 pm
Can someone critique my maths?

There' an infographic doing the rounds on FB, advocating social distancing and  saying
- If 1 person infects 2.5 others every 5 days, then after 30 days you have 406 infections
- If 1 person infects 1.25 others every 5 days, then after 30 days you have 15 infections
- If 1 person infects .625 others every 5 days, then after 30 days you have 2.5 infections

But my rough numbers, when assuming it takes 15 days to become "uninfected and uninfectious" come out as more like 1600, 65 and 0 (it's fudged because doing things in blocks of 5 days doesn't work nicely). Am I wrong or are they?

Saw that and just posted on CD's page.

Isn't it to the power of 6?
If the period is every 5 days, and total is after 30 days, then:
there are 6 of those 5-day periods in 30 days.
So after 30 days,
@ infection rate of 2.5 to power of 6 = 244 people infected
@ infection rate 1.5 to power of 6 = 11 people
@ infection .625 to power of 6 = .006 of a person (doylo, the only one remaining with residual infection)


That's disregarding 'becoming uninfected' which is important in maths terms but unimportant in terms of the message being given.
Caveat I'm a dumbass not a phd

You have to include the original infections i.e. total infections after 5 days = 1 (starting person) + 2.5 (new infections) = 3.5, not the 2.5 that you've assumed. Then 3.5*2.5+3.5 etc... This makes a huge difference after a few cycles.

Interestingly - but obvious really if you think about exponential curves - deducting cases that have expired after 2 weeks makes less difference:
With deductions:1705, 100, 10
Without: 1838, 129,18


Just revisiting this - I noticed a tweet by the mathematician and epidemiologist Adam Kurcharski where he does this same calculation and gets 244. Here: https://twitter.com/AdamJKucharski/status/1239146318301483009

So three different answers to the same problem: '1 person infects 2.5 others every 5 days; after 30 days how many infected?'
No wonder there's confusion about the more complicated stuff!

Your answer, which takes account of the number previously-infected people in each 5-day period, seems to be the correct one when you think about it.. But he's the expert, calculating infection growth rates is surely bread and butter in that field!?

Seems pretty important to the rest of the modelling...Is he right with 244 or are you right with 1600? (I think I can see the infographic answer is wrong).

JamieG

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#1108 Re: Coronavirus Covid-19
March 26, 2020, 04:00:42 pm
In this case Pete what he means is you now have 244 people that are out in public infecting new people. The cumulative number of infected is still 406, just that at the end of each 5 days the old infected are removed from number out in public (i.e. self isolation).

These are the newly infected at each stage 1, 2.5, 6.25, 15.625, 39.0625, 97.6562, 244.1406. Added those numbers up and you get 406.2344 infected.

abarro81

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#1109 Re: Coronavirus Covid-19
March 26, 2020, 04:13:57 pm
His version assumes 2.5 infections total per infected person - they infect 2.5 over the course of 5 days and then, presumably, stay home and stop infecting. In my version they're still out there infecting 2.5 more on days 5-10, then again on days 10-15... then they're removed from the model and stop infecting. I guess the difference between 406 and 1705 shows how important it is to stay indoors and not even go to the shops if you or any in your household have any symptoms!

But yeah, just goes to show that even with the simplest little model there are loads of ways to approach it that could have very drastic influence on the outcomes

petejh

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#1110 Re: Coronavirus Covid-19
March 26, 2020, 04:41:31 pm
Yeah I understand the logic for the three different figures.

What I don't understand so much is which figure represents the reality we live in. It can't be all three. (yep, all models are wrong etc..) So which one is most useful?
As in what do the models assume people who carry the covid infection actually do in real life? They can't all stay at home because they aren't all symptomatic and so won't be aware that they're spreading anything. Obvs this is why the lockdown.

JamieG

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#1111 Re: Coronavirus Covid-19
March 26, 2020, 06:01:48 pm
This response to his original post suggests its much more infectious than 2.5 new infections every 5 days.

https://twitter.com/epsilon3141/status/1239174442770665478

It says the time to double infections is around 2 and a half days. Apparently this gives you 3000 cases by the end of the month. So much much worse. And this seems to hold for the actual data out of Italy, Wuhan and the States.

Stu Littlefair

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#1112 Re: Coronavirus Covid-19
March 26, 2020, 06:12:22 pm
The most common estimate used in epidemiology models at the moment is that it takes circa 5 days from exposure to become infectious and you remain infectious for about 3 days. Some slack in these obviously.

Each person infects on average 2.2-2.5 people.

When you crunch the numbers this gives you the 2.5 people in 5 day figure. 

Offwidth

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#1113 Re: Coronavirus Covid-19
March 26, 2020, 06:17:08 pm
Will's point is correct.

We know that those that are more seriously ill have a higher viral load (more of it in their body) and are therefore more likely to infect others (as more of it expelled into the air/onto surfaces).

What seems to be conjecture is that the seriousness of the resulting illness in the person that catches it is dependant on the strength of the initial dose. Clearly this makes intuitive sense in that the immune system may find it easier to fight off a lower initial dose, and it accords with anecdotal experience of lots of doctors being seriously ill, but I've not seen any evidence for it.

I don't mind posters playing devils advocate on theoretical arguments but in the end when dealing with actions relating to current NHS staff risk not reaching crazy levels it's better to do what can be done on whats likely, given what they are about to face. Health staff need to be careful and good PPE gear is vital. The delays in sourcing what the government said would be provided for PPE is a scandal (and not the only one... but it's a tough game they are playing where even the best intentioned would make mistakes). Here is another recently published mistake (I don't support the lurid headline but am worried about what happened)

https://www.theguardian.com/world/2020/mar/26/no-10-boris-johnson-accused-of-putting-brexit-over-breathing-in-covid-19-ventilator-row

From working for decades around  biomedical research staff I thought it was well establised that for most virus infections the initial infection dose mattered (either single size or cumulatively) in severity of subsequent symptoms. The body's defences have less chance to adapt and defend. I've not seen a paper proving that yet for coronavirus but it's very likely to be the case and it certainly explains the unuusal severity level in young healthy medical staff  treating the most seriously infected. It's  very much best to assume it's true if you want to protect NHS staff as well as you can. If someone wants to see some public explanatory journalistic links google Dr Edward Archer of the London School of Hygene and Tropical Medicine (or maybe email him... academics are human too).  Otherwise for those who prefer arguments to civilised discourse on important topics I can bill  for five minutes at standard rate or at a discount for 10.

Offwidth

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#1114 Re: Coronavirus Covid-19
March 26, 2020, 06:56:49 pm
Another 'U turn' in the last hour (but we still failed to secure those ventilators offered in the link above).

From Guardian live @ 18.25:

"Downing Street announced a U-turn over the EU-wide ventilator procurement scheme. A spokesman for No 10 said the UK did not receive an invitation in time to join in the first effort to procure ventilators and other equipment “owing to an initial communication problem”."

https://www.theguardian.com/politics/live/2020/mar/26/uk-coronavirus-live-news-updates-self-employed-rishi-sunakhospital-car-parking-charges-waived-for-nhs-staff-in-england

spidermonkey09

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#1115 Re: Coronavirus Covid-19
March 26, 2020, 07:17:47 pm
Parents monumentally screwed by that self employed package as it doesn't cover small ltd companies who take dividends. This is a significant proportion of the self employed, surely there will have to be a row back over the next few days...

Offwidth

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Ru

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#1117 Re: Coronavirus Covid-19
March 26, 2020, 07:35:05 pm
I don't mind posters playing devils advocate on theoretical arguments but in the end when dealing with actions relating to current NHS staff risk not reaching crazy levels it's better to do what can be done on whats likely, given what they are about to face. Health staff need to be careful and good PPE gear is vital.

I didn't say it was not likely that greater initial exposure = greater severity. I was just wondering if it had been proven. No one suggested that medical staff should not be equipped for the worst case.

Quote
From working for decades around  biomedical research staff I thought it was well establised that for most virus infections the initial infection dose mattered (either single size or cumulatively) in severity of subsequent symptoms.

It might be well established, but the referenced paper wasn't about that. That's all.

Quote
The body's defences have less chance to adapt and defend. I've not seen a paper proving that yet for coronavirus but it's very likely to be the case and it certainly explains the unuusal severity level in young healthy medical staff  treating the most seriously infected.

That's what I said.

Quote
It's  very much best to assume it's true if you want to protect NHS staff as well as you can.

Agreed. No-one suggested otherwise.

Offwidth

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#1118 Re: Coronavirus Covid-19
March 26, 2020, 07:53:18 pm
An article looking at the situation in the US and speculating about the future.

https://www.theatlantic.com/health/archive/2020/03/how-will-coronavirus-end/608719/

gme

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#1119 Re: Coronavirus Covid-19
March 26, 2020, 08:14:38 pm
Parents monumentally screwed by that self employed package as it doesn't cover small ltd companies who take dividends. This is a significant proportion of the self employed, surely there will have to be a row back over the next few days...
This is what he was hinting at when he mentioned future changes. Limited company status has been pushed by accountants for years to people who shouldn’t really be limited as a way to avoid tax. The rope access industry is full of it.

gme

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#1120 Re: Coronavirus Covid-19
March 26, 2020, 08:17:29 pm
Someone paying a minimum salary from a limited company then the rest of what really should be salary as dividend saves them selves a fortune in tax and also the company saves on NI. The biggest tax loop hole in the country that is used by tens of thousands.

petejh

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#1121 Re: Coronavirus Covid-19
March 26, 2020, 08:33:34 pm
Parents monumentally screwed by that self employed package as it doesn't cover small ltd companies who take dividends. This is a significant proportion of the self employed, surely there will have to be a row back over the next few days...

The self-employed package opens up a huge can of worms.

As someone who for the last ten years has employed self-employed subbies almost weekly and who's got to know many of them and their ...ahem approaches to tax... I can fully appreciate the impossible task of trying to come up with fair financial aid scheme for the self-employed in this circumstance.
Consider for e.g. the offshore worker who boasts of earning £50k and is proud of the fact he doesn't pay a penny in income tax or national insurance - like many of these guys, he runs a 'limited company', pays himself a company 'dividend' and writes off all possible profits that he can against  the purchase of (non-existent) 'essential work equipment and plant' along with various other fraudulent ruses. By the way his father's in the local hospital being treated for a heart attack but he doesn't twig that the treatment's paid for by the taxes he's dodging.
Under this government aid scheme this person will get 80% of 0, because he doesn't make a profit right?
If this person ends up in financial hardship I find it difficult to generate much sympathy for his plight. A proportion of these types of guys (nearly always guys) spend their lives doing their utmost not to contribute their share to the welfare net when it suits them, instead squandering their (inflated) wages on toys.

Then on the other end of the spectrum, the person working from home providing some service or trade, making a reasonable living and who declares all their income. They'll get 80% of their declared profits which seems fair (although a 2 month wait for it).

Somewhere in the middle there'll be various tradespeople who do a range of stuff, on a spectrum of fully working for cash to fully declared for tax. There are so many combinations of circumstances it's hard to come up with something fair to all.

Not trying to be divisive, just that I've dealt with a lot of the former types (and was probably guilty of being one to a small degree a long time ago) and it's interesting to see this play out now they're in need of a state-funded welfare net. Lots of expensive toys going cheap on ebay.. 
« Last Edit: March 26, 2020, 08:41:54 pm by petejh »

gme

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#1122 Re: Coronavirus Covid-19
March 26, 2020, 08:41:53 pm
I am really impressed with what’s been offered by the chancellor so far. Yes there will be some genuine people it doesn’t work for but I think as a whole it puts money in people’s pocket at the bottom rather than how the bank bailout was dealt with.
The one man Ltd company thing is a joke and has been for years.
As a business owner not one thing the government has offered benefits the business at all, all the business has been offered is cash flow help.
The give aways are all to the employees which is how it should be.

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#1123 Re: Coronavirus Covid-19
March 26, 2020, 08:47:58 pm
Someone paying a minimum salary from a limited company then the rest of what really should be salary as dividend saves them selves a fortune in tax and also the company saves on NI. The biggest tax loop hole in the country that is used by tens of thousands.

I know absolutely nothing about this sort of thing to be honest, but on an instinctive level being say a single person rope access worker who is a Ltd. company has always seemed a bit of an odd one. There are no huge set up costs, or indeed ongoing costs / liabilities which require Ltd. status. And semantically being the sole shareholder just seems weird for a start (not really sharing is it?). They are sole traders.

All that said, I would happily rather see the tax loopholes used by large corporations closed as a priority.

As an aside, a lot of companies seem quite happy to be the sole employer of self-employed people on effectively a full time basis, rather than make them employees with increased rights, to save themselves a few bob on NI and holiday pay...as always these things cut both ways.

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#1124 Re: Coronavirus Covid-19
March 26, 2020, 08:52:34 pm
They were already clamping down on one man Ltd companies with the IR35 reforms. They’ve been postponed to next April now due to the virus. The offshore brigade all going ape about having to go PAYE as you can imagine.

 

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