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. 2024 Feb 28:12:1324033.
doi: 10.3389/fpubh.2024.1324033. eCollection 2024.

The spread in time and space of COVID-19 pandemic waves: the Italian experience from mortality data analyses

Daniele Del Re #  1 , Luigi Palla #  2 , Paolo Meridiani  3 , Livia Soffi  3 , Michele Tancredi Loiudice  4 , Martina Antinozzi #  2 , Maria Sofia Cattaruzza #  2
Affiliations

The spread in time and space of COVID-19 pandemic waves: the Italian experience from mortality data analyses

Daniele Del Re et al. Front Public Health. .

Abstract

Introduction: Italy was the first European country affected by COVID-19. Thanks to governmental containment measures (9 March 2020), the spread of COVID-19 was limited. However, in this context, accurate data assessment is crucial and mortality is a more reliable indicator of the virus spread compared to the count of positive cases. This study aimed to retrospectively evaluate the impact of the pandemic in different areas of Italy using the time series analysis of official deaths and excess COVID-19 deaths.

Methods: Mortality data (23 February-30 April 2022) by Istituto Nazionale di Statistica (ISTAT) were analyzed, including four waves of COVID-19. Previous mortality data (January 2015-November 2019) were used to estimate a Poisson regression model of the pre-pandemic mortality pattern and derive the excess COVID-19 deaths as the difference between the actual deaths number and the extrapolation of the previous mortality pattern to the pandemic period, separately for Northern, Central, and Southern Italy, to compare the impact of mortality across time periods and geographical areas.

Results: Estimated excess compared with official COVID-19 mortality shows that, during the first wave, there was an underestimation of deaths. COVID-19 mortality rate almost doubled the official rate in the North (1.60‰ vs. 0.86‰) and nearly tripled it in the South (0.22‰ vs. 0.08‰). In late 2020-early 2021, official and estimated mortality curves are closer, displaying just a small gap at the start of the second wave. During the fourth wave (end of 2021-early 2022), Northern and Central Italy show reasonable agreement; the South presents a large relative underestimation of deaths (+90% increase), with a large increase in its excess deaths national quota, 9% in the first wave to 42% in the fourth.

Discussion: The results provide a measure of the COVID-19 excess deaths and an unbiased estimate of Italian mortality rates. In the first wave, the gap between official COVID-19 and excess mortality was particularly high and lockdown measures may have reduced the spread of the infection. In the fourth wave, the gap for the South increases again, probably because the healthcare system may not have coped with the prolonged pressure of the pandemic, or for a decreased compliance with the official paper-based mortality surveillance system that could be overcome in the future by digitalizing the process.

Keywords: COVID-19; EuroMOMO; Italy; containment measures; mortality; pandemic.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Deaths per day in Italy since 1 January 2015 shown with a blue histogram. The fitted function to describe the baseline is also shown with a continuous red line. The periods used to fit the baseline correspond to the blue regions, where the impact of influenza and heat waves is negligible.
Figure 2
Figure 2
Excess in deaths per day in Italy 23 February 2020–30 April 2022. Results are compared with the official COVID-19 deaths (light blue line). Death excesses are shown with respect to zero, represented with a red dashed line.
Figure 3
Figure 3
Geographical distribution of Italian mortality excess rate during the first wave of COVID-19 (23 February 2020–30 April 2020) shown in the heat map.
Figure 4
Figure 4
Excess in deaths per day for the first wave of COVID-19 (23 February 2020–30 April 2020) for the whole of Italy (A), Northern Italy (B), Central Italy (C), and Southern Italy (D). Results are compared with the official COVID-19 deaths (light blue line). Death excesses are shown with respect to zero, represented with a red dashed line. The vertical axis defining mortality excess/day uses a scale up to 2300 in the two top graphs (A,B) and a scale up to 300 in the two bottom graphs (C,D).
Figure 5
Figure 5
Excess in deaths per day for the second and third waves of COVID-19 (6 October 2020–23 May 2021) for the whole of Italy (A), Northern Italy (B), Central Italy (C), and Southern Italy (D). Results are compared with the official COVID-19 deaths (light blue line). Death excesses are shown with respect to zero, represented with a red dashed line. The vertical axis defining mortality excess/day uses a scale up to 2,000 in the two top graphs (A,B) and a scale up to 600 in the two bottom graphs (C,D).
Figure 6
Figure 6
Excess in deaths per day for the fourth wave of COVID-19 (1 November 2021–30 April 2022) for the whole of Italy (A), Northern Italy (B), Central Italy (C), and Southern Italy (D). Results are compared with the official COVID-19 deaths (light blue line). Death excesses are shown with respect to zero, represented with a red dashed line. The vertical axis defining mortality excess/day uses a scale up to 1,200 in the two top graphs (A,B) and a scale up to 400 in the two bottom graphs (C,D).
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Grants and funding

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This study was supported by Sapienza University of Rome (Research Project Grant 2020 no. D.R. n. 992/2020 Prot. n. 25415 del 27.03.2020; identification research project no. RM120172B844277E). The content is solely the responsibility of the authors and does not necessarily represent the official views of Sapienza University of Rome.