1/ 🧪🧐 A thread on asymptomatic/pre-symptomatic testing.
Currently we know that COVID-19 may be transmitted from person to person through multiple different routes.
Currently we know that COVID-19 may be transmitted from person to person through multiple different routes.
https://twitter.com/DrVeronikaCH/status/1327679649669926912
2/ The primary transmission paths are currently described as person-to-person contact through respiratory droplets generated by breathing, sneezing, coughing etc. Transfer might also occur through hand contact of fomites.
3/ A more recently suggested route might be the faecal-oral route but data on this route seems scarce.[1, 2, 3]
After infection it takes anywhere between 2 to 14 days for symptoms to develop with a median reported at 5 to 6 days.
After infection it takes anywhere between 2 to 14 days for symptoms to develop with a median reported at 5 to 6 days.
4/ This time from infection until symptoms develop is called the incubation period.[4]
When infected, the virus will start to make copies of itself inside the body. It does this trough a process called viral shedding.
When infected, the virus will start to make copies of itself inside the body. It does this trough a process called viral shedding.
5/ This process plays an important role in transmitting the virus to others and in making people sick. We now know that viral shedding is higher at the time of symptom onset but might happen 48 hours before symptom onset.
6/ This means one can infect others up to 48 hours before having symptoms. This is called pre-symptomatic spread.
7/ Where pre-symptomatic stands for 'happening before symptoms develop'.[4]
Now here's the main part of this thread: there is increasing evidence that a significant number of infected go on to develop no symptoms at all.
Now here's the main part of this thread: there is increasing evidence that a significant number of infected go on to develop no symptoms at all.
8/ These individuals still go on and shed the virus and are thus potentially infecting others. The ECDC reports various numbers on the proportion of asymptomatic cases in various studies.[5] They especially talk about asymptomatic cases in children.
9/ According to a systematic review[6] about 14.9% of the children were identified as asymptomatic.
10/ Other studies seem to indicate somewhat similar numbers at 18%[7] and 16%.[8] It is not exactly clear on how much asymptomatic cases contribute to the spread of the virus, but some not peer-reviewed mathematical modeling studies[9, 10] suggests this might be significant.
11/ Because of this testing without symptoms might not always be pointless. After all, one could be pre-symptomatic or asymptomatic.
12/ But it is currently unknown how well the current golden standard in COVID-19 testing, RT-PCR, performs in this subset of the population.[11] As such the current approach in the Netherlands is to only test potentially infected without symptoms if there is a strong suspicion…
13/ …of a potential infection. For example if there is an outbreak in a nursing home or if contact tracing or corona apps have a strong suspicion that you might be infected. The government is however working on making testing available to people without symptoms.
14/ So yes, it's weird that @DrVeronikaCH her leaflet specifies there's no use in testing without symptoms. The leaflet should phrase it more mildly: "as of yet we don't know the effect of testing without symptoms, the scientific evidence is not clear on this yet.
15/ As such it is currently discouraged but might become available in the near future."
16/ [1] sciencedirect.com/science/articl…
[2] who.int/news-room/comm…
[3] sciencedirect.com/science/articl…
[4] ecdc.europa.eu/en/covid-19/la…
[5] ecdc.europa.eu/en/covid-19/la…
[6] jamanetwork.com/journals/jamap…
[7] onlinelibrary.wiley.com/doi/full/10.10…
[8] thelancet.com/pdfs/journals/…
[9] medrxiv.org/content/10.110…
[2] who.int/news-room/comm…
[3] sciencedirect.com/science/articl…
[4] ecdc.europa.eu/en/covid-19/la…
[5] ecdc.europa.eu/en/covid-19/la…
[6] jamanetwork.com/journals/jamap…
[7] onlinelibrary.wiley.com/doi/full/10.10…
[8] thelancet.com/pdfs/journals/…
[9] medrxiv.org/content/10.110…
18/ @GGDGHORNL Kunnen jullie iets vertellen over het testen van verdachte pre-symptomatische en asymptomatische gevallen? Wat is hier momenteel het beleid in binnen Nederland? Is het in de nabije toekomst mogelijk om zonder symptomen een testafspraak te maken?
19/ @Cas_Bax Kan jij iets vertellen over het preventief testen van verdachte pre-symptomatische en asymptomatische gevallen? Wanneer doen jullie dit bijvoorbeeld? Hoe ervaar jij dit?
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