Asymptomatic SARS-CoV-2 Infections - How rare?

[NW-Bound]

Reading the two official reports from the WHO and the CDC on the SARS-CoV-2 virus and the COVID-19 disease that it causes, I notice the following major discrepancy.

The WHO report on the COVID-19 disease in China released on Feb 25 had this to say about asymptomatic infections with the SARS-CoV-2 virus.

Quote:

Asymptomatic infection has been reported, but the majority of the relatively rare cases who are asymptomatic on the date of identification/report went on to develop disease. The proportion of truly asymptomatic infections is unclear but appears to be relatively rare and does not appear to be a major driver of transmission...

A month later, the CDC report released recently stated the contrary to the above, when studying the passengers on the stricken Diamond Princess cruise ship.

Quote:

Available statistical models of the Diamond Princess outbreak suggest that 17.9% of infected persons never developed symptoms. A high proportion of asymptomatic infections could partially explain the high attack rate among cruise ship passengers and crew...

How to explain the discrepancy?

Note that the WHO report was co-authored by China medical experts. The West learned of the virus outbreak in Wuhan back in January 2020. China did not allow the WHO to go in to observe until mid February 2020. I recall being surprised that the WHO published the report quite quickly after being allowed into China. With the WHO having limited amount of time and access to the "battle front", I would think that the WHO had to rely on a lot of data collected and presented by China. Somehow, that was not corroborated by the field observation that CDC made on the passengers on the cruise ships.

I also recall that the US wanted to send along CDC experts with the WHO, but China did not agree to the request.

Sources:

1) https://www.who.int/docs/default-sou...nal-report.pdf

2) https://www.cdc.gov/mmwr/volumes/69/...cid=mm6912e3_w

[Sojourner]

That is an odd discrepancy, but we're still relatively early in this pandemic. I imagine the true statistics will become much clearer over the next 6-12 months as all the numbers are studied intensively and exhaustively.

The more puzzling question for me is: How do asymptomatic people spread the virus? Everything I've heard and read indicates the virus is spread when an infected person coughs or sneezes, expelling tiny droplets of virus-laden moisture from their lungs and mouth. If someone is asymptomatic, one would assume then they aren't coughing or sneezing very much. Seems to me an asymptomatic person would spread the virus much less effectively, to far fewer people, than would an obviously sick person.

[LOL!]

I don't think any of these numbers make any difference. After all, it seems to me that 100% of infected people are asymptomatic and spreading coronavirus for at least a few hours or days early in their infection.

One might as well assume that everyone one sees is infected including oneself.

[Rianne]

Quote:

Originally Posted by Sojourner That is an odd discrepancy, but we're still relatively early in this pandemic. I imagine the true statistics will become much clearer over the next 6-12 months as all the numbers are studied intensively and exhaustively. The more puzzling question for me is: How do asymptomatic people spread the virus? Everything I've heard and read indicates the virus is spread when an infected person coughs or sneezes, expelling tiny droplets of virus-laden moisture from their lungs and mouth. If someone is asymptomatic, one would assume then they aren't coughing or sneezing very much. Seems to me an asymptomatic person would spread the virus much less effectively, to far fewer people, than would an obviously sick person.

But that one cough or sneeze. I understand the "patient 0 or 0" number or letter has been debunked. But just starting the spread with a droplet from an accidental sneeze that the asymptomatic person did quickly thinking they were not infected thus was less cautious about how they sneezed.

[JoeWras]

Quote:

Originally Posted by Sojourner The more puzzling question for me is: How do asymptomatic people spread the virus?

Talking can be a good way to expel particles. Find a shaft of sunlight sometime and look at yourself or someone else. You may be surprised.

Eating is another way.

By now many of us have heard of these lunch gatherings where someone had it, didn't know, and days later other people got ill. Talking, eating and passing the phone were present.

Quote:

Originally Posted by LOL! I don't think any of these numbers make any difference. After all, it seems to me that 100% of infected people are asymptomatic and spreading coronavirus for at least a few hours or days early in their infection. One might as well assume that everyone one sees is infected including oneself.

Yes. Unfortunately, some people are still going about their business unless their fever goes over 38C. You are right, but few are following that guideline.

"My family is fine. My friends are fine. Let's visit!"

[NW-Bound]

Quote:

Originally Posted by LOL! I don't think any of these numbers make any difference. After all, it seems to me that 100% of infected people are asymptomatic and spreading coronavirus for at least a few hours or days early in their infection...

The difference is the exposure time that an infected person can spread the disease. A truly asymptomatic person can go on spreading the virus for days or weeks. After a while, the infected develops antibodies, which can get rid of the virus hopefully. This period to get rid of the virus, we have not been told.

A patient with symptoms would tend to isolate himself, or is shunned by others. The exposure to the public is more limited.

Quote:

One might as well assume that everyone one sees is infected including oneself.

Yes, once people know and understand that there's an outbreak. A month ago, when nobody around you was sneezing and coughing, why would you stay 6 ft away from them?

Even now, we know people who do not give a darn despite warnings. Spain allowed a big political demonstration in Madrid on March 8, and some soccer games. It is paying a heavy price for that now.

What I am saying is even if everybody starts to practice social distancing now, many seeds have already been sown. Familial spread will continue.

We can still reduce the number of new seeds being cast.

[Sojourner]

Quote:

Originally Posted by JoeWras Talking can be a good way to expel particles. Find a shaft of sunlight sometime and look at yourself or someone else. You may be surprised. Eating is another way. By now many of us have heard of these lunch gatherings where someone had it, didn't know, and days later other people got ill. Talking, eating and passing the phone were present.

Yeah, I've definitely encountered my share of "spray" talkers over the years. And the eating vector also makes sense. But both of these modes of transmission require fairly close contact with others. So I would be far less worried about casual interaction with an asymptomatic person (say, in a grocery store aisle) than an obviously sick person.

[MichaelB]

A South China Morning Post article discussing the WHO claim.https://www.scmp.com/news/china/soci...d-asymptomatic

Quote:

The number of “silent carriers” – people who are infected by the new coronavirus but show delayed or no symptoms – could be as high as one-third of those who test positive, according to classified Chinese government data seen by the South China Morning Post.

I think we don’t understand enough about how this is transmitted. Is he contagion factor the same for all, or are some people “super susceptible”? Likewise, are some people super spreaders? This has tremendous impact on the projections, becasue most of them assume everyone as the same level of exposure.

[JoeWras]

Quote:

Originally Posted by Sojourner But both of these modes of transmission require fairly close contact with others. So I would be far less worried about casual interaction with an asymptomatic person (say, in a grocery store aisle) than an obviously sick person.

Agree. I'm less worried about a walk in the isle than I am of gatherings of people who think they are all good, as I'm seeing proposed on Nextdoorumb.

Quote:

Originally Posted by MichaelB I think we don’t understand enough about how this is transmitted. Is he contagion factor the same for all, or are some people “super susceptible”? Likewise, are some people super spreaders? This has tremendous impact on the projections, becasue most of them assume everyone as the same level of exposure.

Agree we don't know enough. China could do the world a favor and gain a lot of good will by helping come up with a serology/antibody test, and then doing a study on the Wuhan population to ascertain the percent infected, symptomatic, hospitalized and deceased. It would help move toward knowing the silent spreaders and receivers.

But we need a good test first. I've read that some are in development and need to be vetted for false positives from other coronaviruses, etc.

[NW-Bound]

Quote:

Originally Posted by JoeWras Talking can be a good way to expel particles. Find a shaft of sunlight sometime and look at yourself or someone else. You may be surprised. Eating is another way. By now many of us have heard of these lunch gatherings where someone had it, didn't know, and days later other people got ill. Talking, eating and passing the phone were present...

And that's how Italians are falling sick in droves.

Germany now says that any group of more than 2 is a crowd, and levies hefty fines.

Quote:

"My family is fine. My friends are fine. Let's visit!"

If people realize that others can be virus spreaders even though they look fine, perhaps Italy does not have the disaster it has now.

Quote:

Originally Posted by JoeWras Agree. I'm less worried about a walk in the isle than I am of gatherings of people who think they are all good, as I'm seeing proposed on Nextdoorumb.

That's my feeling. I can consciously keep a safe distance from other shoppers. Even so, I have not been back to Costco in a long time, and have not stood in line to get in once. Too big of a crowd, and you will not see me there.

But in a gathering when there's food and booze flowing and people are convivial, that's when the seeds for sorrow are sown and people only realize afterwards. And that's how many countries know to ban restaurants and bars. Late because they did not know, but still better than never.

[Ian S]

It seems to me that the stats for the Diamond Princess are liable to be far more reliable than the WHO China ones. The former is as close as you're going to get to an experiment on humans. It still doesn't explain how the asymptomatic infected spread the disease. Sure maybe through talking in close proximity I guess. When we are out and about now, we've extended the separation between us and others to at least 10 feet and preferable more. We are fortunate in being able to do that due to where we live.

Two weeks ago, my husband and I ordered glasses from Costco. We practiced social distancing as much as we could. Now that our glasses are in, we decided to just pay to have them mailed to us because the optical department is pretty much shut down and they are not doing any fitting/adjustments at this time anyway.

[audreyh1]

Quote:

Originally Posted by Ian S It seems to me that the stats for the Diamond Princess are liable to be far more reliable than the WHO China ones. The former is as close as you're going to get to an experiment on humans. It still doesn't explain how the asymptomatic infected spread the disease. Sure maybe through talking in close proximity I guess. When we are out and about now, we've extended the separation between us and others to at least 10 feet and preferable more. We are fortunate in being able to do that due to where we live.

People occasionally sneeze when not sick. I suspect a lot of infections were spread to other passengers via the crew.

[EveryLady]

"Iceland, which says it’s tested a higher proportion of inhabitants than any other country, found that about half those who tested positive have no symptoms of Covid-19, Thorolfur Gudnason, the nation’s chief epidemiologist, told BuzzFeed News.

https://www.bloomberg.com/news/artic...m-scmp-reports

That's bad for containment (which is lost battle) but perhaps a positive for eventual herd immunity. The WHO-China Study was done hurriedly under still-chaotic conditions in China. The latter-developed data may well be the more reliable.

[EveryLady]

Quote:

Originally Posted by Sojourner That is an odd discrepancy, but we're still relatively early in this pandemic. I imagine the true statistics will become much clearer over the next 6-12 months as all the numbers are studied intensively and exhaustively. The more puzzling question for me is: How do asymptomatic people spread the virus? Everything I've heard and read indicates the virus is spread when an infected person coughs or sneezes, expelling tiny droplets of virus-laden moisture from their lungs and mouth. If someone is asymptomatic, one would assume then they aren't coughing or sneezing very much. Seems to me an asymptomatic person would spread the virus much less effectively, to far fewer people, than would an obviously sick person.

Right before we started social distancing, I watched how often folks touch other objects and then themselves - or the other way around. One friend in particular at a lunch casually wiped the back of his hand across his nose, twisted his nose, played with his napkin, then put the napkin on the bare table.

In the course of an hour he did this multiple times. And he was totally oblivious. I didn't say anything, but we just now spoke on the phone and he told me how he does not touch his face and so he will be fine with just washing his hands once home.

Then like others say, with the disease initially present in the upper respiratory one little sneeze even caused maybe by a stray dust particle might eject a stream of viral spores.

[EveryLady]

Quote:

Originally Posted by NW-Bound That's my feeling. I can consciously keep a safe distance from other shoppers. Even so, I have not been back to Costco in a long time, and have not stood in line to get in once. Too big of a crowd, and you will not see me there. But in a gathering when there's food and booze flowing and people are convivial, that's when the seeds for sorrow are sown and people only realize afterwards. And that's how many countries know to ban restaurants and bars. Late because they did not know, but still better than never.

It seems that contamination is most likely when you spend 30 minutes within 6 feet of an infected person without a mask. I think this assumes no physical contact. Now, of course, you can get unlucky and that random passing stranger sneezes just as a gust of wind comes your way. But, by and large, it appears to be a 'social' disease (or a 'touching' one):

https://www.newyorker.com/news/news-...h-care-workers -- link broken, won't take the time to fix it.

“In Hong Kong, “close contact” means fifteen minutes at a distance of less than six feet and without the use of a surgical mask; in Singapore, thirty minutes.”

.”Those of us who must go out into the world and have contact with people don’t have to panic if we find out that someone with the coronavirus has been in the same room or stood closer than we wanted for a moment. Transmission seems to occur primarily through sustained exposure in the absence of basic protection or through the lack of hand hygiene after contact with secretions.”

[aiken]

Quote:

Originally Posted by EveryLady "Iceland, which says it’s tested a higher proportion of inhabitants than any other country, found that about half those who tested positive have no symptoms of Covid-19, Thorolfur Gudnason, the nation’s chief epidemiologist, told BuzzFeed News. https://www.bloomberg.com/news/artic...m-scmp-reports That's bad for containment (which is lost battle) but perhaps a positive for eventual herd immunity. The WHO-China Study was done hurriedly under still-chaotic conditions in China. The latter-developed data may well be the more reliable.

That could be great news, although it isn't clear to me whether the "half who tested positive have no symptoms", will in fact never become symptomatic? What % of the asymptomatic positives are incubating the virus and WILL eventually develop illness? Still so many unanswered questions.

[NW-Bound]

Quote:

Originally Posted by aiken That could be great news, although it isn't clear to me whether the "half who tested positive have no symptoms", will in fact never become symptomatic? What % of the asymptomatic positives are incubating the virus and WILL eventually develop illness? Still so many unanswered questions.

I assume that officials waited long enough to be sure that they never developed symptoms. Never is a long time, but perhaps 1 month is a long enough time.

The CDC report on the cruise passengers said "17.9% of infected persons never developed symptoms". I guess the word never here means at the end of their 14-day quarantine period.

Did these people eventually clear themselves of the virus? Were the cruise passengers allowed to go home with virus in their body? Maybe "never" means they had no symptoms till they tested negative.

Regarding the contagious potential from these lucky people who were infected and did not even know it, the Iceland report said that

Quote:

One of the 18 patients didn’t develop symptoms, yet the viral load was similar to that of the symptomatic patients, the researchers said, “which suggests the transmission potential of asymptomatic or minimally symptomatic patients.”

[NW-Bound]

Two more points I noticed in the Bloomberg article that EverLady linked to in her post.

Quote:

A report by a joint WHO-China mission last month described such infections as “relatively rare” and not appearing to be major drivers of transmission. “It’s becoming clearer that spread of Covid-19 by people who are asymptomatic or mildly symptomatic may be responsible for more transmission than previously thought; making control of the virus more difficult,” Scott Gottlieb, the former head of the U.S. Food and Drug Administration...

The above means that experts have already recognized the deficiency in the month-old WHO report. The recent CDC report is closer to the truth. That settles the question in my original post in the thread.


Finally, the following is a very curious note.

Quote:

In South Korea, more than 20% of asymptomatic cases reported to the Korea Centers for Disease Control and Prevention didn’t develop symptoms during hospitalization...

No symptoms during hospitalization? South Korea has enough hospital capacity to take in infected people with no symptoms?

Here, Americans with some symptoms cannot even get tested. What a 3rd world country we are.

[EastWest Gal]

Quote:

Originally Posted by NW-Bound Two more points I noticed in the Bloomberg article that EverLady linked to in her post. The above means that experts have already recognized the deficiency in the month-old WHO report. The recent CDC report is closer to the truth. That settles the question in my original post in the thread. Finally, the following is a very curious note. No symptoms during hospitalization? South Korea has enough hospital capacity to take in infected people with no symptoms? Here, Americans with some symptoms cannot even get tested. What a 3rd world country we are.

I agree. Greatest health care system in the world? I think not.

Three points:

1. South Korea had a good viral PCR test early on, and did the classic thing epidemiologists do in an outbreak: Do contact tracing and testing. Without testing of asymptomatic people, you cannot determine the rate of asymptomatic infections. I believe South Korea hospitalized all those testing positive, regardless of symptoms, to disrupt the spread of the infection. Here in the USA, we'll get billed for several thousand dollars just for walking into an ER with any problem, however minor, and we don't have the hospital beds to isolate mildly ill people with COVID-19. South Korea did, apparently.

2. It is too early in the pandemic to do testing for asymptomatic infection. The viral PCR test is done on a nasopharyngeal swab, or on sputum when available. Viral PCR test from blood or body fluids is unreliable, with many false negative tests. Countries are now developing serologic testings. Serologic tests cannot identify acute infections, as they test antibody response. In some infections, early antibody tests can be done to identify acute infection (measurable levels of the acute type of antibodies, known as IgM) vs past infection, with the long term type of antibody, known as IgG). These do not provide rapid diagnosis though, and it can take 4-6 weeks or longer to develop detectable IgG levels to a virus.

3. There are other well known infections which are asymptomatic in large numbers of people. One of these is mumps. 50% of those infected never have any symptoms at all, but develop IgG antibodies. However, mumps can cause meningitis or encephalitis, deafness, pancreatitis, orchitis (inflamed testicles) and male sterility, so we have a vaccine to prevent all the bad stuff. Measles, on the other hand, is almost never asymptomatic.

Given how quickly the numbers started dropping in South Korea, I suspect we will find that there are a higher number of asymptomatic cases than we have suspected up until now. In the long run, this is a good thing, as "herd immunity" may then develop more quickly than expected. This is just a slightly educated guess. Still, one can hope.

[NW-Bound]

Come to think of it, the "hospitalization" of infected asymptomatic South Koreans may be nothing more than a quarantine in a motel or barrack for observation. With them feeling well, there's nothing that's needed to do for them, except to check up on them twice daily, and to give them food. There's no need to waste a precious hospital room to house them.

We cannot even manage to do that quarantine.