Assessment of the Overall Mortality during the COVID-19 Outbreak in the Provinces of Milan and Lodi (Lombardy Region, Northern Italy)

Abstract

Objectives: to describe the overall mortality increase in the provinces of Milan and Lodi - area covered by the Agency for Health Protection of Milan - during the COVID-19 epidemic in the first four months of 2020, compare it with the same time period in the years 2016-2019, and evaluate to what extent the mortality can be directly attributed to the outbreak.

Design: cohort study.

Setting and participants: using a new information system developed during the pandemic, we gathered data on the number of daily deaths in the population residing in the provinces of Milan and Lodi by Local Health Unit (ASST) and age groups. To describe the case fatality of COVID-19, we performed a record linkage with a database specially constructed during the epidemic to identify deaths that occurred in confirmed cases.

Main outcome measures: mortality and excess mortality were analysed by comparing the number of observed deaths in the first 4 months of 2020 with the average deaths of the years 2016-2019 in the same calendar period and with expected deaths, estimated using a Poisson model. Furthermore, a measure of relative risk was calculated as observed/expected ratio with a 95% confidence interval.

Results: the increase in mortality for all causes occurring in the study population in the first 4 months of 2020 was 48.8%, 30.8% for ages between 60 and 69, 43.9% for ages between 70 and 79, and 56.7% for subjects above 80 years of age. Focusing on the epidemic period, from 1 March to 30 April, the excess is quantifiable as more than 2-fold and mainly concerns the population over 60 years of age. The excess mortality was observed in all local health units (ASSTs). The highest increments were in the province of Lodi and the North-East of Milan (ASST Nord). In the ASSTs of Lodi and Melegnano-Martesana the mortality excess was detectable from March 15th, while for the other ASSTs the increase began in the first week of April.

Conclusions: evaluation of overall mortality in the provinces of Milan and Lodi during the first wave of the Covid-19 epidemic showed a significant excess compared to the first 4 months of the years 2016-2019, mainly in the population over 60 years of age. However, this excess cannot be completely attributed directly to COVID-19 itself. This phenomenon was more intense in the Lodi ASST, with daily deaths up to 5 times higher than expected.

Keywords: COVID-19; mortality excess; mortality.