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A few months after the start of the epidemic of Sars on 2 Being able to quantify the real extent of contagion in Italy is not that simple. Official data that the Ministry of Health me the state drawn up thanks to the seroprevalence survey conducted from May 25 to July 15, it seems to limit the epidemic to one million 482 thousand cases. However, according to experts, the number of infected is certainly higher. And the reason lies precisely in the type of research being carried out: serological research, which looks for antibodies, actually has several objective limits. Starting with the share of false negatives.
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“It is possible that after some time – explains Fabrizio Pregliasco, virologist and hygiene researcher at the University of Milan – even in the case studies that I have followed, the positive test will be lost. So very often, not everyone develops antibodies. ‘ Added to this is the representativeness of the sample examined. “In fact, this research has some difficulty in capturing – adds Pregliasco – there was no enthusiasm on the part of the citizens due to the fear of being positive, of having to take a swab to be carried out and get stuck at home”.
THE TIME FACTOR
The reference period for serological tests performed on the population voluntarily is not secondary. “If the investigation were done at another time, it is clear that we could probably find a greater number of people exposed to the infection”, warns Claudio Mastroianni, director of the infectious diseases clinic at the Umberto I Polyclinic in Rome and vice president of Simit. (Italian Society for Infectious and Tropical Diseases). To have more reliable data, “research certainly needs to be done in smaller communities where there have been a high number of infected people, and this could give us important insights. In short, it would be useful if it was rescheduled periodically. Complicating matters is also the question of the public who have been tested, and the many reticent.
“Unfortunately, for seroprevalence the problem of the data obtained is linked to the fact that the sample was not reached. Then there may be a possible underestimation, ”observes Maurizio Sanguinetti, director of the Department of Laboratory and Infectious Diseases at the Gemelli Polyclinic Foundation in Rome and president of the European Society for Microbiology and Infectious Diseases (Escmid). “The initial sample stratified by age, sex, region and social status rather than by profession – recalls Nino Cartabellotta, president of the Gimbe Foundation – contemplated 150 thousand stratified, each one representative of a stratum, but as in that period there was the problem of One of those who tested positive were not offered the swab, only about half of the population agreed to participate. It is evident that today, taking into account that the contagion is increasing, it is probable that the number of immunized people is significantly higher than what the research documented 4 months ago ”. That the underestimation can be around 10 or 20 percent, experts for the moment prefer to consider it a plausible hypothesis.
ASYMPTOMATICS
On some fixed points, based on scientific evidence, however, everyone agrees. Mauro Pistello, director of Virology at the Pisan University Hospital, tenured professor of Microbiology and Clinical Microbiology at the University of Pisa and vice president of the Italian Society of Microbiology, prefers to dwell on scientific knowledge. Last, but not least, that related to the role of asymptomatic patients, who are not always detected and therefore notified. “The main causes for which official data are underestimated – emphasizes Pistello – depend on the fact that there are subjects who have developed a very mild infection, so they have not had symptoms: however, we have shown that the virus exists, it has infection, but have not developed antibodies. There is also a higher proportion of cases that have developed antibodies, for example two weeks after infection, but are then retested after two or three months have no more antibodies. Therefore, it is clear that not all these people have been counted in the total official data. Last updated: 06:25
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