The rapid performed by experienced personnel, for example in a pharmacy, can give 10% false negatives. The percentage increases with devices used at home
In which cases should you have a tampon?
There are three situations: contact with a positive person, the onset of symptoms that suggest Covid and prevention, in view of an encounter with fragile people (immunosuppressed, cancer patients, transplanted). The vaccinated with 2 or 3 doses can become infected, but less than the unvaccinated; they can infect, to an even lesser extent; and are about 95% protected from severe disease. So, in the absence of symptoms or tracking required by the local health authority, they do not need to undergo a tampon.
What types of tests can be used?
Molecular swab is the most reliable for diagnosing coronavirus infection. It is performed on a sample taken at the oropharyngeal level and the margin of error is practically zero, because the presence of the viral genome is detected even in subjects with low load, pre-symptomatic or asymptomatic. Antigenic (rapid) tests are sensitive to viral proteins. There are several types, from immunochromatographic lateral flow (first generation) to immunofluorescent read tests (second generation), which offer better performance. The latest generation tests (immunofluorescence with microfluidic reading) seem to show results that are comparable to molecular ones, if performed in the right way. “The antigen test can give a range of false negatives between 10 and 25 percent, depending on whether it is carried out by an expert, for example in a pharmacy, or not – he says. Pierangelo Clerici, president of the Italian Clinical Microbiologists Association and of the Italian Federation of Laboratory Scientific Societies -. This means that with the quick “do it yourself”, you risk having inaccurate results in one out of four cases, since the positivity is not detected. This happens because it is not easy to carry out the nasal oropharyngeal sampling correctly by yourself which, as we know, must cause some discomfort ».
And the salivaries?
Rapid saliva tests are not recommended, because they do not reach the minimum acceptable levels of sensitivity (ability to detect positives, ie patients) and specificity (ability to detect negatives). They are therefore excluded from the European list of valid tests to obtain the green pass. “The quality of the saliva sample is subject to many variables, for example the time elapsed from food or drink and the way the swab was held in the mouth – underlines Clerici -: in general, tests of this type offer fewer guarantees than those who analyze a nose oropharyngeal sample ».
What is the lancing device?
It is a serological test that measures the presence or absence of antibodies in the blood, but without measuring the quantity. If antibodies are present, it does not indicate whether the infection is ongoing or has occurred in the past.
When is it necessary to undergo a serological test?
At this time it is not useful to carry out this examination (unless requested by a doctor), not even in view of the anti Covid vaccination. In fact, there is no standard method and it is therefore possible to have different results by repeating the test in various laboratories. Furthermore, we do not know the “correlated protection” of Sars-CoV-2, which is the level of antibodies necessary to defend ourselves from infection. “The studies are underway, in mine as in other laboratories – says Clerici -: the data collection will be completed one year after the first mass vaccinations, which began in March 2020. I remember that 5-6 needed for hepatitis B years to come to define the “correlated protection”. In the case of Covid, 12 months will be enough. When the study, which is coordinated by the Higher Institute of Health, will be completed we will know what is the level of antibodies that can really protect us from the coronavirus and all its possible variants “.
December 28, 2021 (change December 28, 2021 | 09:09)
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