Coronavirus Outbreak: Part 2

Since the forum software automatically closed the originally, this thread is a continuation of:


@ryan1 said: “No. But presymptomatic spread does. And in the moment, one cannot tell if you are simply presymptomatic or asymptomatic. Therein lies the rub.”

That is incorrect. That’s why the CDC is no longer testing asymptomatic contacts of cases. If they were worried about presymptomatic spread, they certainly would. In fact, that would be their target population for testing. Instead, they’ve given it up.


My brother and his family got it due to presymptomatic spread. His daughter passed it to them a day before she started exhibiting symptoms. The moment she started with symptoms, she started isolating herself. But it was too late.


We are talking about drivers of the epidemic. While I’m sure that what you say is true, it isn’t the main route of transmission.


When did this change? This is pretty much the complete opposite of everything I’ve read up until now. Presymptomatic transmission is the MAIN source of transmission, because people tend to self-isolate once they exhibit symptoms. So they are contagious, but don’t yet know they are.


You’re talking about how the virus is transmitted with behavioral changes, versus how it is transmitted naturally. Those are two different things. I’m talking about the latter. Also, what’s the evidence that people self-isolate? I think the epidemic is still driven by people who don’t. They don’t self-isolate until they get a positive test back, for the most part, or never get tested at all.

Most cases aren’t diagnosed. We know that- estimates up to 10x as many as we know about. Those people aren’t self-isolating.

I do not know why the CDC changed their policy to not be worried about pre-symptomatic spread. I trust the RKI and ECDC more than I trust the CDC, they are still considering pre-symptomatic transmission to be a large factor (and this required them to change their stance and admit they were originally wrong).

It also doesn’t fit well with my lived experience - just as @ryan1 I also have close-to-home anecdotes that are explained by pre-symptomatic spread.

If a person thought their headache, runny nose, fatigue or anything like this was normal and didn’t realize it was an early Covid symptom, that might not be an official pre-symptomatic case, but if you can tell at the time, it doesn’t matter.

Select quotes:

Similar viral loads in asymptomatic versus symptomatic cases have been reported, indicating the potential of virus transmission from asymptomatic patients [30,42]. A community treatment center study (n=303) from Republic of Korea showed that RT-PCR Ct values for SARS-CoV-2 in asymptomatic patients (n=110, 36.3%) were similar to those in symptomatic patients [30]. The median time from diagnosis to the first negative RT-PCR conversion was 17 days for asymptomatic patients and 19.5 days for symptomatic (including pre-symptomatic) patients. Viral loads in asymptomatic patients from diagnosis to discharge tended to decrease more slowly than those in symptomatic (including pre-symptomatic) patients [30].

Asymptomatic transmission (i.e. when the infector has no symptoms throughout the course of the disease), is difficult to quantify. Available data, mainly derived from observational studies, vary in quality and seem to be prone to publication bias [34,43]. Mathematical modelling studies (not peer-reviewed) have suggested that asymptomatic individuals might be major drivers for the growth of the COVID-19 pandemic [44,45].

Pre-symptomatic transmission (i.e. when the infector develops symptoms after transmitting the virus to another person) has been reported [29,46,47]. Exposure of secondary cases occurred 1–3 days before the source patient developed symptoms [47]. It has been inferred through modelling that, in the presence of control measures, pre-symptomatic transmission contributed to 48% and 62% of transmissions in Singapore and China, respectively [48]. Pre-symptomatic transmission was deemed likely based on a shorter serial interval of COVID-19 (4.0 to 4.6 days) than the mean incubation period (five days) [49].

Major uncertainties remain with regard to the impact of pre-symptomatic transmission on the overall transmission dynamics of the pandemic, which is mainly based on the limited evidence on transmission from asymptomatic cases from case reports and modelling.


Yes. And there’s a lot of that, I believe. But that shouldn’t be listed as an asymptomatic case for the purposes of a study, which is what’s confusing everyone, and which is going to continue. That’s why I don’t trust studies that use patient-reported symptoms in this setting- they are unreliable, and it’s hard to draw conclusions of how the virus is transmitted based on that.

If asymptomatic/presymptomatic transmission is a significant aspect of this epidemic, then quarantines are useless. And that does happen, for instance, with chickenpox. That is a disease that is definitely spread before the index case is symptomatic, and quarantines don’t work.

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By the way, I texted my brother yesterday to find out how he’s doing. If you recall, his daughter was sent home from her job at a camp because a fellow employee was diagnosed with COVID. She came home, and the following day started developing symptoms. She was tested. Within a couple more days, my brother had it as did their youngest daughter. Their youngest son and his wife didn’t appear to catch it…although, they may have, but were only mildly symptomatic. It also was spread to my brother’s daughter-in-law, who lived across the street. So apparently just the act of coming home and hugging/greeting each other led to the spread in a single day.

Anyhow, my brother and niece experienced extremely lethargy and some mental “fog” symptoms for a few weeks. Now, several weeks later, my brother is finally feeling back to himself (although he said he has lost strength and needs to build it back up), but my niece (the one who brought it home from the camp) is still struggling with lethargy and mental fog.


I’m not following your logic. At all.

If people are symptomatic, it typically means they don’t feel well. It is true that if they are symptomatic mildly they might think they have a cold or something else and still go out. And, based on testing, a good percentage of the time they are right…a positivity rate in the 2-18% range shows that people think they have symptoms, but end up NOT having it most of the time.

The CDC makes a clear distinction between asymptomatic and presymptomatic. But it is recognized that there is no way to effectively distinguish the two until later. Which means the presymptomatic people are happily going about their business.

Why has the CDC dropped testing recommendations in the asymptomatic stage? There could be a myriad of reasons…although I expect the major one has more to do with testing resources, and the fact that they can’t convince people to go get tested without any reason at all. I don’t think it is because they think it isn’t a major source of spread. And, as I said, just about everything I’ve read about this suggests that it is the presymptomatic cases that is the major cause of spread. Asymptomatic spread is possible, but less likely.


This NyTimes article uses the term “oligo-symtomatic”

I thought the whole basis for quarantining people who seemed healthy was pre(or oligo-)symptomatic spread.

Here you need to quarantine after being tested regardless of symptoms, and if you test positive you need to remain in quarantine. We have a 24h/24h testing guarantee (which means you can get a test in 24 hours and your results will arrive 24 hours after you are tested).

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But they have a reason, a very good reason. They’ve been exposed to someone with COVID19.

What we’ve stopped doing here as a result of having more cases and fewer tests than we need is to stop doing random population testing, where we did drive-thrus of anyone who wanted a test. That just doesn’t happen anymore.

Again, I’m not saying that asymptomatic/presymptomatic spread has no role in spreading this illness, I’m just saying that it isn’t the main cause.

Also, If 10x the number of cases exist over what have been actually confirmed by testing, and only 30-40% of cases are truly asymptomatic according to the CDC, then MOST cases are mildly symptomatic people running around out there. That may be what’s driving this epidemic. People who don’t think they’re sick.

I don’t actually think we disagree all that much, I am just much stricter regarding what constitutes a presymptomatic case. As a clinician, I’m well aware that patient-reported symptoms can be fuzzy at best.

Exactly. Everything you cite there is based on modeling and laboratory studies of the possibility of presymptomatic transmission. And it does seem possible. Whether this has a big impact IRL remains to be seen.

I have my doubts on that. I mean, sure…if someone thinks they have been exposed, they are more likely to be tested. But even here in Michigan, that isn’t technically enough to allow you to be tested. When my wife and I wanted to be tested after fear of exposure at a funeral (granted, we don’t know if ANYONE actually had it or not there), the “rules” wouldn’t have allowed us to be tested based on that alone. We had to confirm we had symptoms. Now, my wife did have what seemed like mild cold symptoms, and so she could be tested. I didn’t. But I got around it because of a question that asked if I had been requested to be tested by someone. I answered this broadly in that certain recommendations I’d seen suggested you should be tested in a scenario such as mine. So, I put “Yes”, which allowed testing.

Anyhow, point is, in Michigan, the number of tests is huge, while the number of positives is relatively low. This suggests a lot of people are being tested mostly due to symptoms, but coming back negative.

You weren’t in prolonged contact with a confirmed case. That’s a big difference. That’s why I was fairly surprised that the CDC dropped testing the contacts of a confirmed case that as a testing criterion. I mean, I can’t think of a population that’s more likely to have it. I guess they’re counting on people staying in quarantine, but that confidence might be misplaced, IMHO.

I want to add that there’s a term I saw recently that I really like- “undocumented infection”. That puts all unknown cases (presymptomatic, asymptomatic and undiagnosed symptomatic) in one basket, which might be the proper way to look at them at this point. If we can’t tell which is which, it might be best to treat them all alike.


Yeah. This is definitely true.


I’m glad we agree on something, It’s too early in the morning to debate with you & @adusca
I’m already worn out.

Which is actually a good thing, it’s why I like to come here. :wink:


Ultimately, everything we’ve seen played out on this thing makes me think that really, the ONLY thing people should be doing consistently is wearing a mask. I’m not really even concerned with the social distancing (except when unmasked) or even having to sanitize everything. I’m not entirely convinced they are helping much. If everyone would just wear their mask! :roll_eyes:


I think that’s true, and that’s what worries me a little about this restaurant scenario. It seems that spread by air is the main mode of transmission, and it’s something that it has taken the authorities a long time to come around to, because it means it’s harder to control. I would hate for restaurants to be a higher risk, there are a lot of jobs riding on that industry. But if it is so, then they have to remain closed or operating at reduced capacity. Because people can’t keep their masks on in a restaurant.

We are not the only ones discussing the new CDC guidelines:


Also reposting this since the other thread was closed after hitting the 10,000 post limit.

As I mentioned previously, I wish more schools would commit to staying open (or closed). It’s the in-between that makes planning impossible. DS22 is sitting out this semester at a large public school- they are starting with in-person classes but we have a strong feeling it won’t end that way, and the school is over 2000 miles from here, so that’s a pretty big chance for him to take, IMHO.

Edit: Also, just a word about Shepherd schools- from what I’ve heard, they are very high-quality and the town is rightfully proud of their schools. I have a feeling they would educate their kids come hell or high water, FWIW.


My DS21 starts his senior year next week at U of M(ichigan). They are doing some classes in person, some virtually. For my son, almost all are virtual except for one. He’s quite bummed about it. He HATES on-line learning, and feels he’s being cheated out of the education he is paying for since in at least ONE of the classes, they are already eliminating some of the material that can’t be done unless in person.

Fortunately, he lives at home and we’re just a 20 minute drive to campus, so he can come and go easily enough.