The answer comes in less than 10 minutes: positive for Sars-CoV-2, negative for Sars-CoV-2. The rapid test produced in South Korea and used in Veneto has the advantage of highlighting the presence of the virus. “It is not sensitive to antibodies, like previous tests, but to the germ itself – he clarifies Roberto Rigoli, head of Microbiology at the Treviso Hospital and national vice president of microbiologists -. We asked the South Korean company to send us some devices under test because we believe that the rapid test may represent a new diagnostic approach necessary to face the new outbreaks: in recent weeks the manifestations of the virus have moved from hospitals to the territory. In Veneto we see outbreaks, related above all to cases of importation from other countries, such as the case of the entrepreneur returning from Serbia or the more recent return of people from Kosovo ».
How does it work
The test costs 12 euros, against the 18 of a normal pad. The Ulss 2 of the Marca Trevigiana is experiencing this which, announced the president Luca Zaia, “will make the data available to the Spallanzani Institute of Rome and to the Ministry of Health so that consideration can be given to the possibility of including the diagnostic test in the Plan of public health “. «The test is performed in the following way: the nasopharyngeal swab is performed in exactly the same way as indicated in the classical method; the swab is diluted in a test tube with a liquid that stabilizes the antigen; finally some drops are deposited on a support (similar to the one used for the pregnancy test) commonly called “bar of soap”. The liquid begins to migrate and, if the viral antigen is present, it is captured in an area where specific antibodies to Covid-19 have previously been fixed. In case of positivity, the bond generates a chromatographic reaction that generates a red band easily detectable with the naked eye “explains Rigoli. The test has been tested on over a thousand subjects. “It is a screening for which we do not make a definitive diagnosis – adds the expert -: positive cases are confirmed with molecular biology. However, the speed of the analysis allows us to immediately isolate the positive ». In addition to Treviso, other centers are using the device, such as Vicenza and Trento. A study should also start soon in Lombardy.
Professor Rigoli, does the test give true results?
«Yes, out of a thousand samples analyzed in duplicate (that is, with the counter-proof of molecular biology) we only had one false positive and no false negative. But we must proceed with the work because so far we have only tested 40 positives, to have more consistent data we must at least analyze 100 positive subjects in duplicate. The point is that, fortunately, there are few infected subjects in circulation ».
What is the difference between antibody detection devices and those that detect the presence of the virus?
“The former show if there has been an infection, but they cannot rule out the possible presence of the virus. On the contrary, the test we are using in Veneto gives an answer on the patient’s current situation, or if the virus is in his nasopharynx ».
What is the degree of sensitivity?
«Less high compared to laboratory tests on biological samples, but this can be an advantage: only positives with a fairly high viral load are identified: subjects who can get sick and probably infect others. Most of the rapid test negative subjects would probably be positive in molecular biology, but they carry a non-replicating virus ».
Can anyone perform the rapid test, even at home?
«No, it is a swab, so you need a preparation to take the sample correctly. A simple citizen cannot do it, but it is certainly a useful tool for family doctors, who can know in real time if a patient with symptoms has coronavirus infection in progress ».
You said you analyzed swabs with a low viral load: can you explain this point to us?
«In laboratory tests an amplification of the viral genome is carried out so that the germ can be detected by the instruments. In the patients of March and April, very few cycles were enough, each of which doubled the amount of virus, to reach millions of copies of the virus RNA. In many of today’s positives, however, many amplification interventions are needed: this means that a low viral load is present in the nasopharynx. Not only that: in laboratory tests we use three targets, i.e. three parts of the virus RNA. The positives we see today, in addition to having a small amount of germ, often respond to one or two of the targets. This may mean that only parts of the virus are present in their body, not capable of causing disease. We have had several cases of health workers, who are swabbed every 20 days, negative and then returned positive, without having any symptoms: it could be residuals from the previous infection, now harmless ».
Can the rapid test evaluate the amount of viral load present?
«No, but it only identifies the subjects in which the virus is present in significant quantities, therefore it makes a sort of” selection “of those that we evaluate as false positives, that is people with a viral load so low that they cannot be considered contagious. For the moment we are using it in patients who arrive in the emergency room, to avoid their waiting hours: until now it was necessary to wait for the results of laboratory tests, which take time. Think of a serious patient or a woman who is about to give birth: being able to intervene immediately makes the difference. Furthermore, plans are being made to extend its use to other realities, such as residences for the elderly and possibly schools, by intervening on the Regional Public Health Plan. The rapid test is a solution to go to the territory and quickly identify the positives, also through the work of family doctors. I would add that in the next few days other devices equal to the Korean one, which already has the CE mark, will arrive on the market. We are already testing some of them. Market competition may perhaps lead to a further drop in prices “.
Are import outbreaks worrying?
“Unfortunately they can become one, we are starting to see some hospitalized patients, even if the numbers are currently reduced. The Venice Zooprophylactic Institute sequenced the virus coming from Serbia, after the case of the entrepreneur who returned to Veneto, and it turned out that it has important differences (mutations) compared to what circulates in Italy. The epidemic is probably in a different phase in that country. We must continue to type the strains and associate their clinical manifestations with them, to understand which strains cause serious disease. Unfortunately we cannot rely on flock immunity which does not exist for this virus: in Italy, according to estimates, Sars-CoV-2 immune is only 2-3% of the population “.
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