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October 23, 2020

Bergamo city and province: the number of people infected by the virus, the rapid serological test and swabs in the Mario Negri study

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Bergamo, 21st October 2020 – The Mario Negri Institute’s study, which will be featured in EBioMedicine – one of the journals belonging to The Lancet publishing group– was conducted in May of this year and involved 423 volunteers: 133 were Mario Negri researchers and 290 were employees of  Brembo S.p.A. Each volunteer underwent a nasopharyngeal swab and two different types of serological tests, in order to evaluate, among other things, performance and reliability.

38.5% of participants tested positive with the serological test and had developed antibodies to SARS-CoV-2. Bergamo is therefore one of the areas with the highest seroprevalence in the world, which far exceeds the current estimated seroprevalence in New York (19.9%), London (17.5%) and Madrid (11.3%).
If the data from the sample are extended to the population of the province of Bergamo, one can hypothesise that up to 420.000 individuals have been exposed to the virus, in contrast with the 16.000 cases that were recorded officially as of 25 September 2020. This would indicate that 96% of COVID-19 cases were missed by the healthcare system.

Luca Perico, first author of the study, stated that “With this study we confirmed that the rapid qualitative serological fingerprick test could be a valid alternative to the quantitative test (ELISA), which necessitates venous blood sampling.” The test, developed by PRIMA® Lab, is comparable to the venous test with regard to sensitivity and specificity. This makes the rapid fingerprick test a very efficient and valuable tool for the identification – within ten minutes – of individuals who have been infected with the virus.

Most individuals who tested positive for Coronavirus antibodies reported experiencing symptoms during the first two weeks of March, though a subset reported experiencing symptoms attributable to Coronavirus as far back as the beginning of February 2020. There are no significant differences between men and women with regard to positivity rates, while positive individuals were, on average, a few years older than those who tested negative.

Of the subjects who tested positive with the serological analysis, only 23 olso had a positive nasopharyngeal swab, which measures the amount of SARS-CoV-2 genetic material found in the nose and throat. These 23 individuals had reported experiencing symptoms in the weeks preceding the test.

Susanna Tomasoni, Head of the Laboratory for Gene Therapy and Cellular Reprogramming, stated that, “Our analysis shows that these are cases with a very low viral load, which leads us to conclude that it was probably too low to be infectious. The data relating to the situation in May suggest that quantifying viral load, rather than simply ascertaining positivity per se, is an important factor in optimising criteria for discharging individuals who have been infected.”
Ariela Benigni, Scientific Secretary and Research Coordinator, concludes “This study has important implications for the containment policies that our healthcare system will have to put in place in case there is a second wave of infections. It also shows us that it would be beneficial if the viral load in every positive swab was also quantified, in order to avoid creating a misleading impression of the situation.”

For further information, please contact:

Ariela Benigni - ariela.benigni@marionegri.it

Luca Perico - luca.perico@marionegri.it

Susanna Tomasoni - susanna.tomasoni@marionegri.it

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