Wednesday, September 27

Antigen test with saliva samples, are they available? are more useful to detect micron?


Some scientific research indicates that taking the sample in saliva is more effective in detecting viral load. The available tests do not yet allow this and the experts explain when it is useful

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A child gives saliva for an antigen test for Covid-19.PHILIPPE LOPEZAFP

In the same way that some people are from the beach and others from the mountains, the different variants of coronavirus also have their preferences about where to set up their camp and reproduce. micron has decided that she it’s more to taste reproducing in the throat while its older sisters had a predilection for the lungs.

we are before a new paradigm shift in this disease that changes our step daily. To begin with, what there is more viral load in the throat can now cause the variant to be more contagious (we spend the day talking) or that among the symptoms we have included a sore throat as a frequent one.

Another novelty are the declarations of experts that during the last days assess whether the traditional way where we are taking the sample is really now the most appropriate.

Are we making a mistake by taking the sample only in the nose? What does Science say? In a study conducted at the University of Cape Town in South Africa, the diagnostic tests of 382 patients with COVID-19 were compared.

in patients with the delta variant of the coronavirus, saliva swabs detected the virus 71% of the time, while nasal swabs found it 100% of the time.

The surprise was that in patients with micron just the opposite happened: saliva swabs detected the virus 100% of the time, while nasal swabs detected it 86% of the time.

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Another recent study has concluded that in the three days before the onset of symptoms and the two days after, the samples of saliva contained about three times as much virus as nasal samples and they were 12 times more likely to get a positive PCR. If this is true, if we were able to detect the positive one day earlier depending on the type of sample, many infections could be avoided.

Although it all sounds very logical, the truth is that both studies (and others with similar characteristics) are preliminary and have not yet been published in scientific journals. The evidence we still have for this is very weak. Being aware of this, many epidemiologists and immunologists in the US have decided to open the melon on the convenience of changing the type of sample collection additionally taking a throat. They believe that despite the inconclusive evidence, we should start making decisions and taking action. The truth is that the coronavirus is always two steps ahead of us. the coronavirus lives inside a song by Chenoa and when we go he has already returned.

What do the health authorities say?

For now the instructions on how to perform the tests have not changed and it is not recommended to do “home experiments” by modifying the manufacturer’s instructions.

In fact, proponents of throat swabs, including one of its greatest exponents, Michael Mina, a former epidemiologist and immunologist at the Harvard TH Chan School of Public Health, nor do they endorse the practice for the general public until there is an approval by regulatory agencies.

That is to say: the experts themselves who have opened the debate and who recognize that they themselves take the double sample at home (throat + nose) they affirm that they do it under their responsibility but they do not encourage the population to act contrary to the instructions of the test. As scientists they admit that this is not the way the tests have been developed and tested and that further investigation is needed.

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What are the drawbacks?

  • In the first place, although it seems that the classic nasal swab tests could be suitable for throat swabbing, it is necessary that they be tested for this purpose since we do not know the number of false positives or negatives that the smear in the throat can cause.
  • On the other hand, there are some practical drawbacks when taking the sample. In some patients it could produce greater rejection (in fact gagging is frequent) or it will be difficult to obtain a correct sample on the palate.

What would the ideal sample collection be like?

Although, as we have explained, it is not indicated to do it for the general population, some experts suggest that the ideal would be a double sample, taken first from the throat and then from the nose.

In fact, in the United Kingdom recommended doing so for a long time and disseminated informative videos to teach the general population how to do it. However, due to the difficulty experienced by many people in taking the sample from the throat later it was decided to simplify and recommend only nasal sampling.

  • First of all, you will have to rub with the swab on the soft part of the palate, on both sides of the bell, and then do the smear in the usual way in both nostrils.
  • It is important to note that to avoid errors You should not eat, drink, smoke or chew gum for 30 minutes before to the test
  • It has been observed, for example, that traces of orange juice could create a false positive in the antigen test.
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Saliva test: the alternative

An alternative that in principle seems simpler to double sampling would be to favor the use of saliva tests. In fact, this week there has been a free delivery of this type of test in Galician schools.

However, there is no evidence or official indication that performing this type of test is preferable to nasopharyngeal tests. For now, both are considered to be equally valid and reliable if done at the right time and in the right way.

In fact, although a priori the taking of the sample seems simpler (“spitting into a tube” is easier than “putting a stick”) the truth is that doing it correctly has a little more crumb.

First of all you have to cough deeply, three to five times, Y push saliva from the back of the throat into the mouth to favor that the saliva is not superficial and comes from the throat. This is something that for some people (especially children or older people with dry mouth) can be difficult. If the sample is superficial, we run the risk of false negatives.

In summary: at the moment”we stay as we are“, making nasal tests as directed by the manufacturer, but with the antenna on (and jaws open) waiting for the recommendations to change at any time. Hopefully, for once, we can get ahead of the bug.

According to the criteria of

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