Covid-19, duration of viral shedding, and infectiousness: meta-analysis
thelancet.com
thelancet.com
Self-isolating/quarantining for 10 days after a positive test result, which many regions enforce, seems consistent with these findings (again, if I'm interpreting the results correctly).
Quarantine is mandatory if you had exposure or returned from abroad.
Though, it would very logical as a precaution.
I know people in Poland who avoided getting a COVID19 test because they knew they would have to quarantine if they took the test, and would not have to quarantine if they didn't. That's perverse incentives for ya'.
It's very hard to enforce, of course, but if you get caught, there are (in abstract) severe fines.
So it's not pointless in that sense. You know who might have been exposed.
It's also not pointless for monitoring spread.
Was somebody in that profile only contagious up until day 9?
Edit: https://www.medrxiv.org/content/10.1101/2020.05.27.20115238v...
Check out Figure 1 and the Discussion section for a good overview.
Everyone is different but by the time people are in the hospital on respirators they're usually suffering from the follow on effects of either direct viral damage or their own immune system going nuts.
Also, there has to be above a certain viral load to be contagious. I am however far from qualified to even guess what the thresholds are and I would think that it is mostly a matter of definition.
Many of the worst symptoms aren't related to the presence or absence of the virus itself. If someone is turning blue from lack of oxygen, it isn't that the virus is doing anything here and now. It is that their lungs are non-functional from damage that the virus already did (note: past tense). You could remove every trace of active coronavirus from them and while they'd probably not get worse they also wouldn't get better very quickly. New lungs don't grow overnight.
If you get shot, you still have a bullet wound when the bullet comes out.
Why? I thought the body’s (potentially delayed) reaction caused the cough, not the virus
That could also explain the strange heterogenity of the virus spreading - maybe some people have more IgA or have IgA earlier and don't really spread a live virus?
Does anybody know what the data says about how long to wait for symptoms after being in contact with somebody who has it?
This has long been a key question: how much of community transmission is due to truly asymptotic individuals? Michael Mina style Lick-a-Stick daily tests could answer this question and remove the potential errors surrounding symptom self-assessment.
"There were no positive tests amongst 1,174 close contacts of asymptomatic cases."
The originally linked Lancet paper makes a distinction between "viral shedding" and "viral RNA shedding". I think the unanswered question involves individuals in the first week of their newly acquired infection (EDIT: after the incubation period). I hope that doesn't come across as nit picking; the scale and scope of the Wuhan study is impressive but an equivalent study is needed in an area with ongoing community transmission.
I'm assuming it means a full, viable string of RNA, rather than (presumably harmless) fragments of same -- and the fragments we're finding being described here are definitely non-viable. Is that roughly right?
Alive in this context means that it can infect host cells and replicate.
Contrary to what the sibling posts say, that doesn't just require intact viral RNA, which by itself is not infectious, but an intact viral assembly, i.e in this case a lipid hull with various accessory proteins, such as the nucleocapsid that packs the RNA and the spike protein that binds to host cells.
A positive PCR test does not imply infectiousness. Many people who have a positive test are not just asymptomatic, they are not really infected to begin with.
A negative PCR test does not rule out disease. Some people who have a clinical diagnosis of COVID may produce a negative PCR result.
It should mean that a 10-day isolation for positive cases, combined with high frequency testing should have a massive impact on the spread of the virus. That the virus can be found in your body much much later, in an "inactive" state should not have much impact on the spread.
https://www.cbsnews.com/news/trump-backer-charged-with-assau...
So covid-19 is transmissible for up to 83 days once infected?
"Although SARS-CoV-2 RNA shedding in respiratory and stool samples can be prolonged, duration of viable virus is relatively short-lived. SARS-CoV-2 titres in the upper respiratory tract peak in the first week of illness. Early case finding and isolation, and public education on the spectrum of illness and period of infectiousness are key to the effective containment of SARS-CoV-2."
> no live virus was isolated from culture beyond day 9 of symptoms despite persistently high viral RNA loads.
> This finding is supported by several studies demonstrating an association between viral load and viability of virus, with no successful culture from samples below a certain viral load threshold.
So the amount shed is too low to infect anyone beyond 9-10 days (I think, I am not a virologist, etc.)
Is it possible to acquire immunity against the virus (in a similar way that vaccines work) by being in contact with someone at say day 20+?
There is also a similar theory that cloth masks might have the unintended positive side effect of building immunity. They are not perfect, so the virus might still reach its target. But the viral load could be reduced enough that instead of infection it leads to immunity.
This meta analysis only includes studies of multi patients so there's pretty much a guarantee that there are individual case studies that differ from this.
The paper cites 34 replication cycles as the lower bound to obtain viable viral cultures. Whether a PCR test is reported as "positive" depends on the chosen replication cycle threshold (Ct value). As far as I'm aware, this "magic number" is usually chosen to be 35.
Beyond that, it is possible to do more cycles to demonstrate the existence of trace amounts of PCR fragments, but such a test would not be considered "PCR positive".
There are published case reports where someone has tested PCR positive during an infection, then PCR negative, and then PCR positive again later and the explanation given has been that they did not get re-infected and their infection did not flare back up but just that virus had been continually shed and the later test was able to capture that.
edit: s/DNA/RNA. The PCR process actually operates on DNA so the virus RNA is converted to DNA as the first step of RT-PCR.
That does put into question the validity of counting PCR test positives as a benchmark of viral load among the population, but as a safety measure for potentially infected individuals, the trade-off is worthwhile.