Asymptomatic - infection and transmission question

[Catyness]

Has anyone got any research information on asymptomatic infection and transmission? Thought I'd ask the hive mind. of all the clever and informed people on here.

It seems from testing that people can have covid-19 but not have any noticeable symptoms. Do these people go on to develop symptoms - so they are in the pre-symptomatic phase? Or is the test picking up remnants of an old infection from when they did have symptoms? Or are they false positives? Or do people truly have this virus to detectable levels and not get poorly? Why would that be?

The second part of the question is, if people can have covid-19 and never experience symptoms, is there research yet on if they are contagious?

Appreciate these may not be answered yet but hopefully research is at least being done as it seems rather important information.

Thanks!

I am being routinely tested at work. I tested positive but never developed symptoms at all but my dd did get symptoms about 6 days after I tested positive so I’m pretty sure she got it from me.

A friend of mine was in hospital with an ulcer, he had the test and was told that he had antibodies and was asked when he had covid. He said he hadn’t experienced anything other than a slight cough in January.

I can only partially answer your question.

Being asymptomatic doesnt mean you necessarily go on to develop symptoms, some do and some dont. If you do, you were pre symptomatic at the time of testing, rather than being asymptomatic.

If you are pre symptomatic then you most certainly can transmit COVID- that's mostly how it spreads now that people are more careful. If you are asymptomatic the picture is less clear ie no-one knows for sure - partly because it's pretty tricky to know with certainty where an individual got infected. I was exposed to a presymtomatic colleague 5 days before I got sick but I cant be sure that is how I caught COVID. I then went on to infect dh whilst I was pre symptomatic and he went on to infect the kids, one of whom was asymptomatic. That chain of infection was pretty clear.

I certainly believe that symptomatic individuals are likely to be more infectious than asymptomatic ones but there seems to be a wide variation in how infectious individuals are anyway, look at "super spreaders".

I can't answer all your questions but it is much harder for an asymptomatic person to pass on Covid-19 as they are not distributing air droplets through coughing to the same extent as a symptomatic person. However, if you live with someone then the increased exposure would override that minimising factor. But for the general public it is harder for the asymptomatic person to infect people, especially with hand sanitising/washing and masks.
Both cases are true: you can asymptomatic and then develop symptoms or asymptomatic and never get symptoms.
And there are false positives - people would rather highlight the false negatives though as these involve public risk rather than personal inconvenience. There are issues with dead virus genetic material and replicating a tiny amount of virus to make it detectable in a PCR test that for other viruses would not qualify for a positive result and would be marked negative. But for Covid-19 they are reporting these very low levels as positive - apparently.

My husband and his colleagues have had antibody tests- they work for the Nhs but not patient facing. One of them had high enough antibody levels to be eligible to donate convalescent plasma. He had no symptoms at all, has worked from home throughout and doesn't know anyone who's had it. Doesn't help with the question of asymtomatic transmission but gives me hope that more people have got antibodies than we're aware of

It's all a complete mystery

There was an imperial college epidemiologist and mathematical modeler on The Life Scientific yesterday. His statement was that infected asymptomatic people were less likely to pass it on. Which makes sense as 1) they have a lower viral load and 2) not sweating/ coughing means there’s fewer routes for the virus to get out and onto others.

I work on the coalface of covid response -- PP responses are good.

I wouldn't say complete mystery, but there's always some uncertainty. All of the high quality evidence points to covid being mostly (probably overwhelmingly) transmitted by direct contact with droplets. Contagious person needs to do something to spit those droplets out or it's very unlikely to transmit.

Do these people go on to develop symptoms - so they are in the pre-symptomatic phase?

Most often yes one study I'm involved in, those without symptoms who had a positive test majority got symptoms within 2 weeks. The others remained truly asymptomatic. Other studies have similar findings.

Or is the test picking up remnants of an old infection from when they did have symptoms? Or are they false positives?

Test picks up matching RNA, but the RNA may not be viable (so unable to infect anyone). So post-symptomatic positives are very possible. % of false positives is probably small. There are a few different PCR tests on the market, I'm not sure how reliable each one is.

Or do people truly have this virus to detectable levels and not get poorly? Why ?

Some people can have high viral load & not be sick: nobody knows why. Also The tests are very sensitive is why they can detect levels that are so low that they can't make a person feel ill. We don't know why some immune systems stop virus from making people feel ill. It's normal with most infections that some people get it bad & others barely at all. Zika & polio are good examples: symptoms can range from nothing to very bad or even lethal.

The second part of the question is, if people can have covid-19 and never experience symptoms, is there research yet on if they are contagious?

Hot topic in active research! Likely to be low-to very low risk for infecting others, for reasons others said. But low risk is not Zero risk.

Thank you for such well thought out answers. If it wasn't so serious and stressful it would actually be quite and interesting subject.