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Mystery in Wuhan: recovered coronavirus patients test negative then positive

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Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#111

Post by bewaretheirs »

W4ldi wrote: post #62
bewaretheirs wrote: post #45

Earlier quoted context omitted.

They're highly sensitive to the presence of the target DNA or RNA sequence in the sample well. But they can't easily tell if the target sequence they amplified came from the patient's sample or from other potential sources of contamination in the lab (the test, after all, makes billions of copies of the target DNA sequence), whether from other positive tests or from positive controls.

But that doesn't explain false negatives, does it?

They typically do one swab of the nasopharynx (upper back of the throat, up above the soft palate). You might have the virus elsewhere but not there.

Saw reports that bronchoalveolar lavage (introducing and then suctioning out fluid from a branch of the lung) is better at picking up virus if it's present -- but it's much more time consuming, more invasive, and much less pleasant for the patient than sticking a swab up your nose. Not something you're going to do in a parking lot in a drive through testing center for someone only showing mild symptoms.

There are always compromises.

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#112

Post by devy »

perl4ever wrote: post #101
devy wrote: post #94

Earlier quoted context omitted.

Yep! CT scans and clinician's experience is more reliable than any tests for COVID-19 diagnostics (which should only serving as a definitive confirmation). This also why I believe human doctors are still unbeatable by AI

I think that's missing the point, which is that the only way to get the necessary accuracy is to use multiple independent sources of information. It's not whether clinicians are better than tests or vice versa, but that no single datum is good enough.

No. The point is, COVID-19 testing kit is in extreme short supply everywhere in the world right now given most countries are locked down and the viral outbreak patients are growing at an exponential rate, the next reliable way to diagnose COVID-19 for clinicians without testing kits is to use CT (which gets results fast and inexpensive and the equipment is universally accessible in every hospital) scans and find some patterns, which is exactly what doctors in Wuhan did during the early phase of the outbreak[1].

[1]: https://www.ncbi.nlm.nih.gov/pubmed/32134681

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#113

Post by devy »

davnn wrote: post #102
devy wrote: post #94

Earlier quoted context omitted.

Yep! CT scans and clinician's experience is more reliable than any tests for COVID-19 diagnostics (which should only serving as a definitive confirmation). This also why I believe human doctors are still unbeatable by AI

> This also why I believe human doctors are still unbeatable by AI. Because you hypothesize that they can rapidly learn new, not very distinctive patterns without much data?

> hypothesize

Of course not! We've got half a million cases now, hundreds of thousands cases in hospitals, and hundreds of papers published in all the medical journals. So yeah, data is rich.

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#114

Post by cjbprime »

DeonPenny wrote: post #77

You've locked healthy people inside with sick people during the quarantine. Wouldn't that cause some reinfections? After your immune system got beat down the first time.

Catching a virus normally provides you immunity for some time frame from three months up to years or forever. We aren't expecting reinfection (yet) because we're expecting immunity, but might be wrong.

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#115

Post by tehjoker »

dirtyid wrote: post #104
devy wrote: post #94

Earlier quoted context omitted.

Yep! CT scans and clinician's experience is more reliable than any tests for COVID-19 diagnostics (which should only serving as a definitive confirmation). This also why I believe human doctors are still unbeatable by AI

I remember an article early in the outbreak that Chinese doctors found the most reliable diagnosis comes from CT scans. Test was merely the first filter. They tuned the settings to increase scan speed at the cost of resolution and setup a process to scan up to 200 patients a day per scanner. I wonder if this is still best practice that other countries aren't adopting. On the other hand I expect tests to have improved…

My doctor friend who got the minutes of a call with a chinese doctor said they were also swabbing multiple areas of the body for PCR and doing an antibody screen as well (in addition to CT).

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#116

Post by davnn »

devy wrote: post #113
davnn wrote: post #102

Earlier quoted context omitted.

> This also why I believe human doctors are still unbeatable by AI. Because you hypothesize that they can rapidly learn new, not very distinctive patterns without much data?

> hypothesize Of course not! We've got half a million cases now, hundreds of thousands cases in hospitals, and hundreds of papers published in all the medical journals. So yeah, data is rich.

I was mainly referring to CT scan data. A symptomatic check should not require much experience, rather applying the knowledge in form of a simple decision tree.

Regarding CT scans .. machine learning will be so much better than humans in classifying those once enough data is available... it‘s completely out of question for me as an ML researcher.

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#117

Post by rumanator »

robocat wrote: post #71
rumanator wrote: post #63

Earlier quoted context omitted.

> I have seen realistic assessments of the ultimate effectiveness I'm afraid we only see the chinese government's report and data on how the epidemic is spreading within China.

I think China is mostly telling the truth. Firstly, exports are hard to lie about. Order something from alibaba yourself, or here’s some graphs: https://www.plex.com/blogs/china-potential-model-for-post-co... Secondly, Trump would break that news if it were fact. Hiding 10’s of thousands of deaths and 100’s of thousands of very ill is extremely difficult in the modern world when relatives live overseas. Thirdly, I be…

Your points boil down to:

a) China keeps on exporting,

b) liars are caught and Trump didn't caught the Chinese regime lying,

c) The Chinese regime enforced quarantined effectively.

From these points, only the third has any relation with and impact in the outbreak of covid19 within China.

However, as the virus is reported to have an asymptomatic incubation period that can be as long as 2 to 3 weeks, and as there are reports from within China that show that covid19 can be transmitted at over 4 meters, then, as we have seen in Italy and Spain, the impact of this measure would only start to show with that much of a lag.

I admit I am not an epidemiologist, but claiming that an epidemic was just stopped on it's tracks almost instantly has little to no credibility. For that to be even remotely realistic, there needed to be zero asymptomatic carriers from one day to another.

To add insult to injury, the Chinese government reported that the only new covid19 cases experienced within China came from foreigners who imported the disease.

I'm sure the measures imposed by the Chinese regime has a profound impact on the epidemic, but none of the official reports appear to have any credibility whatsoever. A disease with a 1 to 3 week incubation period does not stop spreading or killing people from one day to the other. What does stop immediately is how you chose to report the data, specially counting the dead.

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#118

Post by rumanator »

scribu wrote: post #84
robocat wrote: post #71

Earlier quoted context omitted.

I think China is mostly telling the truth. Firstly, exports are hard to lie about. Order something from alibaba yourself, or here’s some graphs: https://www.plex.com/blogs/china-potential-model-for-post-co... Secondly, Trump would break that news if it were fact. Hiding 10’s of thousands of deaths and 100’s of thousands of very ill is extremely difficult in the modern world when relatives live overseas. Thirdly, I be…

Whoever's downvoting this comment, how do you refute the point that export numbers are hard to fake? It would collusion from all of China and all of the importing countries.

> how do you refute the point that export numbers are hard to fake?

By the fact that there are already reports of factories throughout the world that kept operating eventhough they were experiencing an outbreak of covid19 within their staff.

And let's be honest: no one places China in the top spots in rankings on safe working conditions and human rights.

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#119

Post by baxtr »

bewaretheirs wrote: post #111
W4ldi wrote: post #62

Earlier quoted context omitted.

But that doesn't explain false negatives, does it?

They typically do one swab of the nasopharynx (upper back of the throat, up above the soft palate). You might have the virus elsewhere but not there. Saw reports that bronchoalveolar lavage (introducing and then suctioning out fluid from a branch of the lung) is better at picking up virus if it's present -- but it's much more time consuming, more invasive, and much less pleasant for the patient than sticking a swab u…

It depends on the time of the illness. Roughly my understanding is: 1st week - high virus load in the nasopharyngeal area. 2nd - almost no virus load in the nasopharyngeal area, high virus load in the lungs

Re: Mystery in Wuhan: recovered coronavirus patients test negative then positive

#120

Post by perl4ever »

devy wrote: post #112
perl4ever wrote: post #101

Earlier quoted context omitted.

I think that's missing the point, which is that the only way to get the necessary accuracy is to use multiple independent sources of information. It's not whether clinicians are better than tests or vice versa, but that no single datum is good enough.

No. The point is, COVID-19 testing kit is in extreme short supply everywhere in the world right now given most countries are locked down and the viral outbreak patients are growing at an exponential rate, the next reliable way to diagnose COVID-19 for clinicians without testing kits is to use CT (which gets results fast and inexpensive and the equipment is universally accessible in every hospital) scans and find some…

Well, that's your point, but I think everyone knows the tests are scarce.
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