#MSCOVID19: Asymptomatic Shedders

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Barts-MS rose-tinted-odometer: ★

The reason why so many people are coming down with COVID-19 and the second-surge is truly surging is the observation that three-quarters of people who are actively shedding SARS-CoV-2, i.e. have positive tests, are asymptomatic at the time of testing (see the latest study below).

In summary, having symptoms suggestive of COVID-19 is a very poor marker of whether or not you are infected with the virus and shedding. Therefore the only way to reduce the spread of the virus in the community is to assume that everyone who you come in contact with is infected and shedding. Therefore social distancing, masks, handwashing, avoiding high-risk environments, etc. becomes critical in slowing down the spread of the virus. 

Saying that there are many scientists and probably most politicians who are actively supporting the spread of the virus in low-risk communities, for example, University students, as an attempt to increase herd immunity. The danger of the latter is that it is very difficult to contain the virus in these low-risk communities and as a result, it is already spreading into high-risk groups which is why we are beginning to see an increase in hospital admissions and deaths from COVID-19. 

It is clear that we have many months still to run with this pandemic and sadly many more lives will be lost. On a positive note, the observation that many people in the general population and probably in the MS population as well, seem to have pre-existing cross-reactive immunity to the virus and hence seem to be resistant to infection. This means that we may get herd immunity at a population level much quicker than we expected. 

The latter may explain why the second-surge is not nearly as bad in London compared to some of our Northern cities, for example, Liverpool, Manchester and Newcastle. Many more people were infected in London in the first-wave, i.e. we have more herd immunity, which is acting as a firebreak and slowing down the spread in London. 

To paraphrase Robert Frost, we have many miles to go before we sleep. There is little doubt that 2020 is going to be a long hard year. We have just had to cancel our travel plans for Christmas; a small price to pay for being healthy and alive. Please try and stay positive things will get better; time is a great healer.

Stopping by Woods on a Snowy Evening
BY ROBERT FROST

Whose woods these are I think I know.
His house is in the village though;
He will not see me stopping here
To watch his woods fill up with snow. 

My little horse must think it queer
To stop without a farmhouse near
Between the woods and frozen lake
The darkest evening of the year.

He gives his harness bells a shake
To ask if there is some mistake.
The only other sound’s the sweep
Of easy wind and downy flake.

The woods are lovely, dark and deep,
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep.

Petersen & Phillips. Three-Quarters of People with SARS-CoV-2 Infection are Asymptomatic: Analysis of English Household Survey Data. Clinical Epidemiology. 8 October 2020 Volume 2020:12 Pages 1039—1043.

Background: To reduce transmission of SARS-CoV-2, it is important to identify those who are infectious. However, little is known about what proportion of infectious people are asymptomatic and potential “silent” transmitters. We evaluated the value of COVID-19 symptoms as a marker for SARS-CoV-2 infection from a representative English survey.

Methods: We used data from the Office for National Statistics Coronavirus (COVID-19) Infection Survey pilot study. We estimated sensitivity, specificity, the proportion of asymptomatic cases (1 – sensitivity), positive predictive value (PPV) and negative predictive value (NPV) of COVID-19 symptoms as a marker of infection using results of the SARS-CoV-2 test as the “gold standard”.

Results: In total, there were 36,061 individuals with a SARS-CoV-2 test between 26 April and 27 June 2020. Of these, 625 (1.7%) reported symptoms on the day of the test. There were 115 (0.32%) with a positive SARS-CoV-2 test result. Of the 115, there were 27 (23.5%) who were symptomatic and 88 (76.5%) who were asymptomatic on the day of the test. Focusing on those with specific symptoms (cough, and/or fever, and/or loss of taste/smell), there were 158 (0.43%) with such symptoms on the day of the test. Of the 115 with a positive SARS-CoV-2, there were 16 (13.9%) reporting symptoms. In contrast, 99 (86.1%) did not report specific symptoms on the day of the test. The PPV for all symptoms was 4.3% and for the specific symptoms 10.1%. The specificity and NPV of symptoms were above 98%.

Conclusion: COVID-19 symptoms are poor markers of SARS-CoV-2. Thus, 76.5% of this random sample who tested positive reported no symptoms, and 86.1% reported none of those specific to COVID-19. A more widespread testing programme is necessary to capture “silent” transmission and potentially prevent and reduce future outbreaks.

CoI: multiple

Twitter: @gavinGiovannoni  Medium: @gavin_24211

About the author

Prof G

Professor of Neurology, Barts & The London. MS & Preventive Neurology thinker, blogger, runner, vegetable gardener, husband, father, cook and wine & food lover.

12 comments

    • No, I am being optimistic and referring to 2020, which we are three-quarters through. I think 2021 is going to be a very different year; it is going to be ‘alive with the sound of people mingling and being social’.

      I am particularly looking forward to going to listen to live jazz and to show my support for our musicians and the entertainment industry 😉

      • I like thinking of what we will be able to do again one day!

        I’m looking forward to being able to go into my childrens’ school and see them in plays again and having harvest festivals and Christmas fayres and sports day again. Please let this happen in 2021!

  • Yep, that is what a vaccine will do. Population-based herd-immunity including high-risk people. Let’s hope there are not too many anti-VAXXERs.

    • It appears given the current rate of increase in infections, that government incompetence will get us well on the way to herd immunity (assuming there is such a thing for Covid) by default well before any vaccine is likely to be available.

  • Great advice. Assume everyone is infected and shedding. I’ve been doing this since the whole pandemic kicked off. Maintaining social distance, limiting high risk environments (e.g shopping centres), washing hands, working from home and wearing a mask in public. A pretty lousy life at the moment but things will improve. I live in Sydney where contact tracing is excellent and we have minimal community transmission. With that said, the government is now pushing for restrictions to be further reduced and we haven’t really experienced a second wave (like Melbourne). So, when it hits (and it will), it’s likely to be far worse than the first wave in April….

    Stay safe people and be kind to each other.

  • “there are many scientists and probably most politicians who are actively supporting the spread of the virus in low-risk communities, for example, University students, as an attempt to increase herd immunity. The danger of the latter is that it is very difficult to contain the virus in these low-risk communities”

    I know a young person who has had COVID-19 and is now still dealing with symptoms, i.e. “long covid”. This is a very nasty, unpredictable disease. So no one should talk lightly of letting it rip through young people.

  • Many more people were infected in London in the first-wave, i.e. we have more herd immunity, which is acting as a firebreak and slowing down the spread in London.

    That’s sheer conjecture, wishful thinking isn’t it? It’s spreading in London too. And Glasgow is being hit hard, again?

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