Covid-19 in Milan before the start of the epidemic


We know it by now. When February 21 was identified on Patient 1 in the Codogno Hospital, the CoViD-19 epidemic was already widespread. But how much it was, and how long, it is still a debated issue. Now, a study carried out on the blood donors of the Polyclinic of Milan between February 24 and April 8, sheds new light on that initial phase that has been ignored by official counts: it has been observed that, in the last week of February, 4.6% of donors – that is 1 in 20 – had already developed antibodies to the new coronavirus, SARS-CoV-2, a sign that the disease had already been around for some time, since the immune response is not immediate. In early April, the figure had risen to 7.1%, moving towards higher age groups. What do these data mean? We see it immediately.

Unexpected cases. The study – conducted by Daniele Prati and Luca Valenti, of the Policlinico, in collaboration with the Luigi Sacco Hospital, the European Institute of Oncology and the University of Milan – covers 800 donors, which are a significant sample – albeit not directly representative of the entire population of the city, because “they are healthy subjects with public health issues, aged between 18 and 65”, explains Daniele Prati, creator of the research, director of the Department of Transfusion Medicine and Polyclinic Hematology. So these people were asymptomatic, indeed, completely unsuspected. But asymptomatic, unfortunately, they can be very infectious.

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Hunting for antibodies. Together with routine tests, each of the donors was subjected to an antibody sensitive serological test that the immune system produces against SARS-CoV-2. And two types of antibodies have been traced: IgM immunoglobulins (a sign of a recent infection), and IgG (a sign of long-term immune memory). To speed up its spread, the study was published in MedRxiv without peer review, that is, without having been controlled by the scientific community yet. The results, therefore, must be considered preliminary.

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First the young people, then the elderly. In its essential lines, the picture that emerges is that the virus presumably arrived in Italy between late December and early January. It began to spread underground from the second half of January, initially mainly among young people. By the time Patient 1 was identified, thousands of infected people were already circulating in Lombardy, but they were largely asymptomatic or had mild symptoms. Then the virus reached the weaker sections of the population, and things went as we unfortunately know. In the meantime, hygiene and social distancing measures have had their effect: they have blocked the spread, especially among young people. And traces are also seen in the blood of donors.

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