[The impact of the COVID-19 pandemic on the Italian and foreign population in the various phases: the results of an interregional multicentre project]

Objectives: to analyze the difference of the SARS-CoV-2 infection impact between Italian and foreigner subjects, evaluating the trend of infections and access to diagnostic tests (molecular or antigenic swabs for the detection of SARS- CoV-2) in the two different populations, inducing the detection of new positive cases in the population.

Design: retrospective population study for the period February 2020-June 2021.

Setting and participants: Italian and foreign resident population on 1st January of the years 2020 and 2021 in the Regions participating to the project: Piedmont, Lombardy, Veneto, Emilia-Romagna (Northern Italy), Tuscany, Lazio (Central Italy), and Sicily (Southern Italy).

Main outcome measures: in the two populations, for every week and aggregated by macropandemic period were calculated: • the test rate (people tested on the population); • the swab positivity rate (positive subjects on those who are tested); • the new positives (positive subjects on study population); • the percentage of foreigners among the new positive cases. The ratio of the value of the indicators in the foreign and Italian populations (with 95% confidence interval) was calculated to evaluate the association between nationality (Italian vs not Italian) and outcome. The analyses were conducted at the regional level and at pool level.

Results: the trend of new positives by nationality (Italian vs not Italian) has a similar tendency in the different pandemic waves. However, the incidence of new positives during pandemic waves among foreigners is lower than in Italians, while it tends to increase during intermediate periods. Except for the summer periods, foreigners are less tested than Italians, but the percentage of new positives out of the total of new ones tested is higher among foreigners compared to Italians. The relative weight of new positives among foreigners tends to increase in periods with the greatest risk of inflow of SARS-CoV-2 for foreigners.

Conclusions: the epidemic trends in the two populations are similar, although foreigners tend to show lower incidence values, probably in part because they are tested less frequently. Furthermore, in foreigners compared to Italians, there is a greater risk of contracting SARS-CoV-2 infection, especially in periods of relaxation of containment Coronavirus measures, reopening of national borders, production and commercial activities.