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Testing people with coronavirus symptoms

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 jonny taylor 18 May 2020

I'm puzzled by the apparent emphasis on testing people who *already have symptoms of Covid19*. This seems rather back-to-front to me - surely it makes sense to focus limited testing resource on people who don't have symptoms, but who you really don't want to be spreading the disease (e.g. medical staff, care home workers). I know there is increasing amounts of that precautionary testing going on (as announced today in Scotland, for example), but it seems odd that that's not the main priority.

Anyone fancy speculating about why that is? The only purposes I can see would be to reassure those who have symptoms that turn out not to be Covid that they can continue without self-isolating, monitoring mutations of the virus, or providing certainty for epidemiological tracking. I'm no expert, but I'd have guessed that picking out asymptomatic spreaders in vulnerable areas would be at least as important as any of those factors...

In reply to jonny taylor:

If you are separating care facilities into 'COVID' and 'non-COVID' sides, then it's probably a good idea to know into which side patients should be sent (false negative rate here is the worry).

In order to identify the asymptomatic, you'd have to keep regularly testing the entire population (less the already positive results). Which we clearly cannot do with the resources we have.

If you assume that prior infection confers immunity (unconfirmed so far, but more normal for such infections), then those found to be previously infected might continue life less restricted, and would need no further testing. Depending, that is, on the false positive rate of the test, and the ability for tests to detect previous, overcome infections (which doesn't seem the case except for more complex antibody tests by the likes of Porton Down), and the social acceptability/public health risk of such a move.

If you want to know the extent of the real problem, and distinguish COVID-19 from other coronavirus or influenza infections, which present similar symptoms, you need a test to distinguish them.

If you're looking to see the extent to which the disease has spread within the population, then carefully-designed randomised testing might be performed (which I think is the case).

Just a few thoughts.

Post edited at 14:13
 fred99 18 May 2020
In reply to captain paranoia:

> In order to identify the asymptomatic, you'd have to keep regularly testing the entire population (less the already positive results). Which we clearly cannot do with the resources we have.

But what could be done is test those in highly vulnerable situations who are not showing symptoms - front line NHS, care home and ambulance staff for example - in order that they don't spend a few days prior to showing symptoms unnecessarily infecting their fellow workers and families. Waiting until they have it is a bit like shutting the stable door after the horse has bolted. This might also give a more accurate assessment of whether their PPE levels are actually doing the job.

Post edited at 15:17
 marsbar 18 May 2020
In reply to captain paranoia:

You could just test those who are front line dealing with the public.  

I thought testing and tracing was the plan.  Apparently not.   

In reply to marsbar:

> I thought testing and tracing was the plan.  Apparently not. 

No, apparently not:

https://www.ukclimbing.com/forums/the_pub/nhs_study_into_asymptomatic_cv19_positive_staff-719546

 wintertree 18 May 2020
In reply to jonny taylor:

Best practice in clinical care for covid patients are diverging from those for other diseases with the same symptoms, so I can see it makes a difference to the individual’s care.  As most “pillar 1” testing only done on hospital admissions and there is an unusually high barrier to hospital admissions this seems justified.

It allows one to separate wards and staffing along covid carrier status, balkanisation being a powerful way to lower transmission.  No idea how much that is actually being done mind you.

Most of the new testing capability is going to the kind of workers who risk spreading the disease.  It’s hard to really know though as there’s overlap in the definitions of pillar 1 and pillar 2, and pillar 1 numbers are rising as well.

 jt232 19 May 2020
In reply to captain paranoia:

Just because you test someone in Monday doesn't mean they don't have CV on Tuesday so you would have to constantly retest people. 

The NHS alone employes over 1 million people, plus care workers, plus and other 'front line' staff. Currently the UK sometimes does over 100,000 tests per day, but the actual number of people tested each day is much less. I just don't think there is anywhere near enough capacity for what you are suggesting.

In reply to jt232:

> Just because you test someone in Monday doesn't mean they don't have CV on Tuesday so you would have to constantly retest people

errrr....

"In order to identify the asymptomatic, you'd have to keep regularly testing the entire population (less the already positive results). Which we clearly cannot do with the resources we have."

I think you may have replied to the wrong person...

Post edited at 01:00
 jt232 19 May 2020
In reply to captain paranoia:

Apologies, meant to reply to the OP

Post edited at 05:23
In reply to jt232:

Good replay

In reply to Self service bd limited:

Is it me, or is it unclear exactly what antigen testing and swab testing is suppose to achieve other than provide a headline figure for the government to glean a tiny bit of credit for?

I can see that testing patients when they enter hospital is good, especially as care pathways for Covid diverge from other treatment plans; I can see that regular testing of asymptomatic frontline workers would be excellent; once a day would be good, (if not too intrusive), but once a week would still be (almost infinitely) better than never, which according to some people of this parish still appears to be the case.

And antigen testing of sample populations seems to be a good way to study how prevalent the disease is and has been in the population at large, for the majority of which will always be asymptomatic . 

But I've been watching those briefings and it's not clear that the government or their various advisers and bureaucrats have a clear idea of what to do, other than to being seen to be doing SOMETHING.

  

In reply to Rob Exile Ward:

Surely one also needs to swab test infected health and other key workers to make sure that they are no longer an infection risk and can go back to work. (This also applies to patients released back to care homes, and even other patients going back to an uninfected household or workplace).

There was a thread yesterday where I think a paramedic was saying  that a colleague had been off several weeks and kept testing positive, sending an assumed virus negative paramedic back to work untested is bad. Ideally there probably should be two swab tests before returning as there is apparently a high % of false negative results.

Research sampling of the population for antibodies against the virus seems obvious and is apparently being done at least by Porton Down. One assumes there is similar swab testing of the population.

As you say they do seem to concentrate on impressing us with number of tests done, rather than coordinating or targeting them to best effect.

In reply to oldie:

> Surely one also needs to swab test infected health and other key workers to make sure that they are no longer an infection risk and can go back to work.

Post-treatment confirmatory diagnostic tests don't appear to be something widely used in medicine, in my limited experience. X-rays are rarely taken to confirm bones have healed after six weeks, for example. Most other 'maintenance' disciplines would routinely test that repairs had fixed the problem. I wonder if this apparent belief in treatment regimes has something to do with the approach in this case. Any medics please correct me if my impression is incorrect.

Or maybe it's a numbers game again; what is the probability that an infection will not have passed within 7 days? vs the chance of them becoming a super-spreader due to their close contact role.


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