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The tests for Covid-19 are more than one, based on different techniques, offered by the public and the private, more or less quickly. The very rapid and predictable evolution that, with the passage of time, new technological developments allow the creation of even more reliable and faster kits.
In Italy the diagnostic system organized by the National Health Service designed in such a way that Avoid as much as possible the DIY trend by citizens.. For this reason, swabs, or at least “positive” swab results, should be communicated to the Health Protection Companies (former ASL) both by the public and by the private entities that carry them out.
Performance of a test are generally measured according to two main indicators: the “sensitivity”, or the proportion of positives, in this case of infected subjects, correctly identified, where a high sensitivity corresponds to a few false negatives and “specificity”, or the proportion of negatives, individuals who are not infected, who are correctly identified, where a high specificity corresponds to a few false positives. In particular, to correctly identify coronavirus positives, therefore, the test needs to have a high “sensitivity”.
Tests from different brands may have different characteristics with respect to cost, time required to result, and sensitivity. Some are “validated” by the Higher Institute of Health (ISS) and by the Technical-Scientific Committee (CTS). Not necessarily that individuals (or public laboratories) necessarily use validated tests; In general, there is a wide freedom of choice (and experimentation): the variables related to the different tests used are not easy to “control” by a citizen.
Hyssop
The buffer or molecular buffer or PCR (from the English “Polymerase Chain Reaction”, polymerase chain reaction) or RT-PCR (from the English “Reverse Transcription Polymerase Chain Reaction”, the main test of diagnosis for pandemic control, the method recognized and validated by international organizations to make diagnosis, that is, detecting the presence of the Sars-CoV-2 virus in an infected individual. The test must be processed by specialized personnel in a microbiology laboratory with complex reagents and machinery. That is why the handling of tampons has been entrusted to public centers or by convention.
Material
The test is performed on a sample of respiratory secretionsIt is usually taken with a nasopharyngeal swab.
How the withdrawal occurs
Harvesting is done with sticks inserted into nostrils and / or pharynx.
What is it based on
The hyssop a molecular assay based on the recognition of the virus RNA (nucleic acid) by a viral amplification method (PCR).
Response times (result)
1-2 days from collection, 2 to 6 hours from arrival at the laboratory. Times vary a lot depending on the type of machines supplied to a laboratory, the available personnel and the number of swabs to be processed at any given time. The ability to test large numbers of people is often one of the standards that positively or negatively rates a state’s efficiency in controlling the coronavirus epidemic.
Reliability
The sensitivity of the buffer averages 98%. (In essence, out of every 100 infected, one molecular swab correctly identifies, on average, 98). Obviously it also depends on other variables, for example, how the sample was taken, whether the swab was not inserted deep enough, for example, or whether the screening was done in the inappropriate time. When a patient is tested too early (during the incubation phase) or at the end of the illness, the amount of virus may be too low to be detected.
Outcome
The swab can be “Positive” and indicates that a person contracted the virus and was infected at the time of collection, or “negative” and indicates that the person does not appear to have contracted the virus. and be infected at the time of collection. As they say, the “photograph of a moment” because a topic can be negative today and positive tomorrow. Not only. “Positive” does not necessarily mean “symptomatic”, since there are people who have the virus but remain without symptoms (the so-called “asymptomatic”) and it does not necessarily mean “contagious.” We know that the maximum contagion occurs in the 48 hours before the onset of symptoms and for about 7 days thereafter (although there are cases up to a maximum of 14 days). There are situations in which a person remains “positive” for months, but after a certain period of time they are no longer contagious: the swab is so sensitive that it finds traces of viral RNA from it, but they are “harmless” virus fragments, unable to replicate. The “positive” result in Italy is obligatorily reported to the competent health authorities.
When should it be done
Whenever someone believes that they have had the opportunity to become infected with Sars-CoV-2 and as a screening (at school, at work) or to find out the positivity of categories with higher risk of contagion (such as doctors and nurses). The tampon is decided and prescribed by the doctor-pediatrician-ATS. If it’s done too soon with respect to the date on which the contagion (exposure) is assumed, it can be negative (that’s why we speak of “false negative”). The false negative rate at least 8 days after exposure, or 3 days after the onset of symptoms (on average and if any). For this, scientists recommend rubbing no earlier than 72 hours after the suspected infection, to minimize false negative results.
In private
I can decide to do it privately (although it should be a doctor to evaluate when it is more advisable to do it, see above the problem of “false negatives” ed). In case of “positive”, the result will be communicated to the competent health authorities.
How much
In private it costs on average between 80 and 150 euros.
What happens when I rub (me and my family)
After running a swab, the result is awaited in isolation. In case of a positive result, the ATS takes over the person and organizes the selection of close contacts:obligation of isolation for the person who took the test and quarantine for close contacts (They are family members or classmates or colleagues). Isolation and quarantine end for themselves or close contact when two subsequent swabs are negative or after 14 days in case you haven’t cleaned. The need to have negativity in two swabs, however, questioned by many scientists who indicate how a single negative time could be sufficient to indicate successful resolution of the infection. Some countries (like France) have also halved the length of quarantine. In Italy there was the hypothesis of taking it to 10 days, but for now the Scientific Technical Committee (CTS) has confirmed the 14 days.
Salivary swab / salivary test
The diagnosis can also be made by rubbing a small amount of saliva. Again, this is a molecular biology test. (“classic” swab) made with different techniques. They can give a result in the laboratory within 5-10 minutes. Salivary swabs are used in some countries in the world (such as the USA and Japan) especially when massive screening is necessary, so it is necessary to know in a short time the positivity of groups of subjects considered at risk. High sensitivity, but, even in this case, it depends on the kits used. In Italy, experiments with this type of test are being carried out, but have not yet been validated by the Ministry of Health.
“Quick” swabs or “antigen tests” or “bars of soap”
Other rapid diagnostic swabs have been developed that detect the presence of the virus in infected individuals. They are already used in Italy at airports or when they serve as mass control (as happened with the return of countries considered “at risk” such as Croatia, Spain, Malta and Greece). They work differently than traditional tampons: they are based on the detection of viral proteins (antigens) present in respiratory secretions. Also in this case the sampling is done with sticks inserted in the nostrils and in the pharynx., or saliva can be collected. The answer “yes / no” as for the pregnancy kits and it arrives on average in 30 minutes. No special training is required for reading and the result does not require laboratory tools. The answer (but it depends on the models) comes in minutes. They have a sensitivity of 80-85%, less than “classic” tampons: recognize around 80-85 out of 100 infected. If a person has a low amount of the virus in their body, the test could give a false negative result. Sometimes they look like “bars of soap” or “credit cards” with colored bars.
September 24, 2020 (change September 24, 2020 | 10:47)
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