The coronavirus testing dilemma: quality or quantity?

PANDEMIC

Swab, serological examination and rapid test: we assess current methods for detecting COVID-19 infections

The coronavirus testing dilemma: quality or quantity?
The coronavirus testing dilemma: quality or quantity? © Shutterstock

The coronavirus testing dilemma: quality or quantity?

The coronavirus testing dilemma: quality or quantity? © Shutterstock

After the surge in infections recorded in recent weeks and the imminent overlap with seasonal flu, the need to carry out more and more tests, and rapidly is becoming crucial. With the Swiss laboratories already under pressure, the solution could be so-called ‘rapid tests’, which could provide results in minutes. But what types of tests are available? And what would be the pros and cons of moving from current to ‘rapid’?

Nasopharyngeal molecular test - but we all call it swab

Widely used in Switzerland and around the world, this type of examination involves the taking of a sample by inserting a stick, a sort of cotton swab, into the nasal cavity. The analysis in the laboratory then allows to ascertain on the sample the presence or absence of the RNA of the virus, the genetic material with which it reproduces. The accuracy of this test is considered very high, with the main problems represented by the invasiveness of the same and the relatively long times for obtaining the results (from a few hours to a day or two).

The usefulness of the serological test: understanding the real incidence in the population

With serological (or immunological) tests, the laboratories look for, in the blood samples taken, the presence of antibodies against the coronavirus: if found, the logical deduction is that the patient must have come into contact with COVID-19. The problem lies in the fact that serological tests are very useful to understand how many have been infected (symptomatic or not) and already cured, less so to understand who has an infection still in progress. Their reliability in identifying ‘currently ill’ is therefore usually considered lower than that of swabs, while its statistical value for understanding the actual long-term incidence is unmatched.

Quick tests: remedying shortcomings in quality through quantity

Although rapid molecular tests are spreading (which identify, like the swab, the presence of the virus RNA), the most talked about test in recent weeks is the antigenic one. Faster than molecular swabs (we are talking about 15-20 minutes of waiting for the result) and very practical, it would allow to ascertain the presence or absence of coronavirus proteins in the patient. These, in fact, would trigger a chemical reaction if put in contact with the coronavirus antibodies. The trouble is that this type of test is generally considered less reliable than the molecular one. According to swissinfo.ch, for example, the antigenic that Roche developed reported a 3.8% higher probability, than tampons, of generating a false negative to therefore provide a negative result to a patient who is actually positive for coronavirus. This disadvantage, according to some experts, could be compensated by the possibility of making the antigenic rapid an examination carried out more frequently.

And while some countries have already decided to embrace the philosophy of quantity over quality (the US announced the expenditure of 760 million dollars for the production of multiple antigen tests between August and September), what will Switzerland do? To alleviate the urgency on the laboratories, considering that rapid tests could also be managed by qualified medical personnel, even our country could one day focus on quantity.

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