Testing at airports

[Alex50]

A chap was on BBC news this morning saying testing at airports is nearly 100% accurate even if you asymptotic, he is suggesting people can pay for this at the airports so they don’t have to quarantine, why don’t the government suggest this?

Maybe because they only work if you have active virus at the moment you test? If you are infected but 3 days, or 8 days off developing symptoms the test will be useless.

If you mean the guy from the airline industry on R4 just now, I thought he was talking out of his arse.

So what’s the point of testing? What about NHS staff if they have no symptoms, tested negative, does that mean the test maybe questionable? Does that make all the negative tests questionable who don’t show symptoms?

Testing shows you don’t have it today. If you have symptoms and get a negative test, then the symptoms aren’t from covid. (With the proviso that the tests aren’t totally accurate!)

Large scale testing of people without symptoms is to find people who are asymptomatic and is useful in groups where lots of people are being exposed - e.g. nurses.

But to escape quarantine I suppose you’d need a test every morning with instant results, and we don’t have those yet.

So that means tests don’t work whether you don’t travel or not? You could catch it anywhere and be spreading it, all negative testing is questionable then?

You may have a cold and also have Covid but could still test negative as you are asymptotic as you have only just caught Covid, that means all negative tests are questionable?

Every test has a failure rate - false negatives (ones that look negative but are really positive) and false positives (look positive but are really negative).

For Covid - the false negatives are what we want to minimise. We can use the test in such a way as to reduce the risk to an acceptable level - eg initial test then isolate for 5 days then another test (btw - numbers of repeat tests and duration are just given as examples as I don’t know the stats for that test).

That means the government numbers are wrong, there could be many more people who are testing negative that are positive?

Do we know what % of tests are correct?

Wrt NHS/care staff the weekly testing shifts out a certain number of those who are positive but asymptomatic. Anyone with symptoms knows to isolate and get tested. It's a pretty robust way of lowering transmission in an environment where people are at constant risk of contracting COVID.

What the tests are not able to do is to pinpoint people who have contracted coronavirus but are still currently in the process of developing COVID. The virus needs a number of days to multiply up to high enough numbers to trigger a positive result. In most people that takes around 3- 5 days, in others it can take up to 14. Which is why if you think someone may have COVID the best thing to do is to quarantine them for 14 days.

So it can take 14 days to come out without showing a positive test? Then surely after 14 days you can still spread it? I thought to control this virus we needed a rigorous track and trace system, how can that work if many people are walking round thinking they’re negative when they could be positive? None of this makes sense? How can schools go back in September if our testing system can’t pick up the virus for 14 days?

You are being facetious. The test and trace programme does not ask people to get tested after contact for just this reason and requires contacts to isolate for 14 days even if they get a negative test. The numbers of people who are both symptomatic from another illness, are in the early stages of Corona and have not been in contact with another person who tested positive is going to be so small to be completely insignificant on a population level, so it is safe to consider those who test negative with symptoms and who have not been in contact with a confirmed case to not have the virus in most circumstances and such people are only allowed to return to normal life when symptoms disperse in any case.

Well Germany seems to think it’s better to test than isolate for 14 days.

www.theguardian.com/world/2020/jul/27/bavaria-rolls-out-coronavirus-mass-testing-for-returning-holidaymakers

Just because Germany thinks something doesn't make it accurate. If you believe what the Germans say so much maybe you should consider going to live there.

So how will it work when schools go back, my daughter is in a bubble of 260 children they will get colds flu but say they have a negative test do they still need to isolate for 14 days? If so no one will ever be at school.

@Alex50- surely if schoolchildren are being tested it will be because they have developed symptoms. If it’s corona, and it’s at the stage where they have developed symptoms, it will show up on a test. The problem with testing people at the airport is that it won’t have had time to reach the symptoms/show up on a test stage.

I hope so but it sounds like if you have symptoms but test negative you still have to isolate for 14 days just in case the test was incorrect? I’m not sure how it will work if you can’t guarantee result on a negative test?

No, if you have symptoms and test negative you do not need to quarantine.