Temporal dynamics in total excess mortality and COVID-19 deaths in Italian cities

Abstract

Background: Standardized mortality surveillance data, capable of detecting variations in total mortality at population level and not only among the infected, provide an unbiased insight into the impact of epidemics, like COVID-19 (Coronavirus disease). We analysed the temporal trend in total excess mortality and deaths among positive cases of SARS-CoV-2 by geographical area (north and centre-south), age and sex, taking into account the deficit in mortality in previous months.

Methods: Data from the Italian rapid mortality surveillance system was used to quantify excess deaths during the epidemic, to estimate the mortality deficit during the previous months and to compare total excess mortality with deaths among positive cases of SARS-CoV-2. Data were stratified by geographical area (north vs centre and south), age and sex.

Results: COVID-19 had a greater impact in northern Italian cities among subjects aged 75-84 and 85+ years. COVID-19 deaths accounted for half of total excess mortality in both areas, with differences by age: almost all excess deaths were from COVID-19 among adults, while among the elderly only one third of the excess was coded as COVID-19. When taking into account the mortality deficit in the pre-pandemic period, different trends were observed by area: all excess mortality during COVID-19 was explained by deficit mortality in the centre and south, while only a 16% overlap was estimated in northern cities, with quotas decreasing by age, from 67% in the 15-64 years old to 1% only among subjects 85+ years old.

Conclusions: An underestimation of COVID-19 deaths is particularly evident among the elderly. When quantifying the burden in mortality related to COVID-19, it is important to consider seasonal dynamics in mortality. Surveillance data provides an impartial indicator for monitoring the following phases of the epidemic, and may help in the evaluation of mitigation measures adopted.

Keywords: COVID-19-related death; Demographic factors; Mortality displacement; Surveillance system; Total excess mortality.

Fig. 1

Distribution of COVID-19 confirmed cases by province (rates by 100,000 resident population, data up to May 4th) and location of the Italian cities included in the study (The map has been generated using R statistical software and the source of the shape file is the Italian Institute of Statistics released with Creative Commons License – Attribution – 3.0)

Fig. 2

Mortality trends^a before and during the COVID-19 outbreak by geographical area^b. Footnotes. ^a Panel a and c show daily deviations between observed and baseline mortality, together with COVID-19 daily deaths for Northern and Central and Southern Italy respectively. Panel b and d present daily trends in net excess mortality (e.g. total mortality after removal of baseline and COVID-19 deaths) with parametric curve derived from natural spline with 3 degrees of freedom (red line) and 95% confidence bands (light blue shaded area) for Northern and Central and Southern Italy respectively. ^b Panel a and b: northern Italy (12 cities); panel c and d: central and southern Italy (19 cities)

Fig. 3

Cumulative mortality differences^a before and during COVID-19 outbreak, by geographical area^b, age and sex. Footnotes. ^a Green and red bars represent cumulative differences between observed and expected deaths before and during the COVID-19 outbreak, respectively; yellow bars show cumulative COVID-19 deaths. ^b Panel a: northern Italy (12 cities); panel b: central and southern Italy (19 cities)