Mapping the COVID-19 epidemic in Lombardy, Italy, years 2020–2022: a population-based study of temporal trends, geographic distribution, and risk factors for incidence, hospitalization, and mortality

Background In late winter of 2020, the first locally transmitted outbreak of COVID-19 in Europe was reported in Lombardy, Italy. This study provides a comprehensive analysis of the epidemic’s trajectory in this heavily impacted region from March 2020 to the end of 2022. Methods We conducted a cohort study utilizing anonymized data from Lombardy’s eight local public health authorities (LPHAs). The dataset included all individuals registered with the Regional Health Service as of January 2020, with monthly data aggregated by sex, age, country of origin, municipality or ZIP area, and comorbidities. SARS-CoV-2 lineage data from the regional repository allowed us to segment the study period into four sub-periods by predominant viral lineages. We report the temporal trends and geographical distribution of three outcomes (COVID-19 incidence, hospital admissions, and mortality) as well as COVID-19 test positivity rates and vaccination coverage across LPHAs and Local Health Districts (LHDs). Multivariable regression models were employed to identify key risk factors for COVID-19 incidence and mortality in each of the four sub-periods. Results We describe the impact of the COVID-19 pandemic over a population of 10 million people, of whom 45% were aged ≥ 50 years and 22% had a history of cardiac diseases. The outbreak was concentrated, in the early phases, in a few LHDs, none of which had large cities. As soon as the SARS-CoV-2 transmission increased in the population, hospital admission and mortality decreased over time, especially for areas impacted early. Our results confirm the role of age and neurologic and renal comorbidities, as well as geographical location, hinting at the impact of local epidemic dynamics and health system factors on both outcomes. Conclusions Our findings provide essential insights into the dynamics of COVID-19 in one of Europe’s earliest and most severely affected regions, contributing valuable evidence to the global understanding of pandemic management and public health responses.