Impact of COVID-19 on foreign population resident in urban areas of Italy: selection of indicators, data sources, and definition of geographical stratification levels

Objectives: to describe indicators, data sources, and levels of geographical stratification used within the framework of the CCM project "Epidemiological Surveillance and Control of COVID-19 in Metropolitan Urban Areas and for the containment of SARS-CoV-2 circulation in the immigrant population in Italy".
Design: population-based observational study based on data from the Integrated Covid-19 Surveillance System and the archive of hospital discharge records.
Setting and Participants: interregional collaborative project. Resident population in 5 Italian Regions (Piedmont, Emilia-Romagna, Tuscany, Lazio, and Sicily).
Main Outcomes Measures: crude and age-standardized rates of diagnostic test utilization and positivity, hospitalization (in any department and in intensive care unit), and mortality in COVID-19 cases.
Results: starting from the set of 11 indicators from the Italian National Institute for Health, Migration and Poverty (INMP) project "Epidemiology of SARS-CoV-2 Infection (COVID-19) and Use of Health Services in the Immigrant Population and Vulnerable Population Groups in Italy", the five most effective indicators for CCM purposes were identified. The INMP project highlighted higher rates of test access and positivity among Italians compared to foreigners, higher standardized hospitalization rates among foreigners, and higher standardized mortality rates among Italians, with geographical and temporal heterogeneity. The intersection between the DEGURBA (degree of urbanisation) classification and altimetric zones defined five levels of territorial stratification characterized by decreasing population density. Approximately 81% of the population involved in the CCM project resided in the first two levels; 43% of Italians lived in areas with intermediate population density in hilly or plain areas, while 48% of foreigners were concentrated in densely populated areas.
Conclusions: sharing the collaborative approach and a research methodology already tested, integrated with the analysis of disaggregated indicators by morphological, functional, and administrative characteristics of the residential territory, allowed for assessing differences in the impact of the pandemic between Italians and foreigners residing in more or less densely populated areas.