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Swabs and serologic tests, how to speed up COVID-19 diagnosis

The capability of testing as many people as possible is becoming an essential element to contain the contagion and defeat the COVID-19 virus.
The number of swabs performed daily is increasing all over the world, but the lack of laboratories able to process the tests, together with the prohibitive costs of its execution, determined an initial delay, partially responsible for the spreading of the pandemic.

The test currently used for the diagnosis of the COVID-19 infection is the very well-known swab: a stick like an ear cotton swab is rubbed against the mucosa of the mouth or nose (posterior or upper pharynx), then undergoing molecular tests by real time PCR that is able to confirm the presence of the virus.

The swab test is for the moment the more reliable method: it allows, among other things, to identify asymptomatic subjects, usually difficult to find out but carrying the virus transmission, and to consider any mutation of the virus undergoing the test to avoid false negative outcomes.

This is a method requiring specific equipment and materials, and that can therefore be carried out only by specialised virology laboratories. For this reason, in the last weeks, a hunt to ‘rapid tests’ has started, namely diagnostic procedures yielding immediate results and much cheaper, that can at least exclude immunised people from the picture of the pandemic management.
Serologic tests and rapid swabs have been under discussion in the last few days, with interventions of experts and health authorities on their safety and reliability.
The serological test is performed on blood and shows the presence of some antibodies forming after the contagion in the serum of the patient. If the test detects these antibodies, then the immune system of the patient was in contact with the virus.

These tests can be carried out with a blood withdrawal or even with a lancing device, as for rapid test for blood sugars, but they still have some dark side. They cannot say when he person was infected: according to the available data, coronavirus antibodies would form at least after 8 days from the onset of the symptoms, and early testing could yield negative results.
Moreover, not all serologic tests are able to detect the quantity of antibodies produced by the immune system. ‘Rapid’ serological tests only detect their presence. Only quantitative serologic tests, looking for the presence of IgG antibodies, the last to form, can confirm that the infection occurred long before and that the patient could be immunised. For the latter, a drop of blood is not enough, a blood sample is needed.

While their reliability is still under discussion, the Ministry of Health gave the green light to rapid molecular tests (CE-Ivd and/or Eua/Fda, aslo called Point of Care tests, Poct), able to detect viral genes directly in the secretions of the airways mucosae. They also take much time – only few samples at the time can be processed – but they are a useful support for infections to be urgently diagnosed.

The memorandum letter released by the Ministry also includes a list of diagnostic kits and certified companies manufacturing and distributing them. The list, drafted by the in vitro diagnostics working group of the Technical Health Committee at the Ministry, reminds us in fact that, as in vitro diagnostics, the kits to carry out these tests have to be authorised by the competent authorities.
The registration of serological tests and rapid swabs shall therefore take place according to the provisions of Directive 98/79/EC currently in force, taking into account the priorities identified by the Ministry memorandum. The support of consulting companies specialised in the registration of medical devices and in vitro diagnostics can help to market these products quickly.

Written by: Maria Pia Felici