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. 2020 Dec;25(49):2000790.
doi: 10.2807/1560-7917.ES.2020.25.49.2000790.

Epidemiological characteristics of COVID-19 cases and estimates of the reproductive numbers 1 month into the epidemic, Italy, 28 January to 31 March 2020

Flavia Riccardo  1   2 , Marco Ajelli  2   3   4   5 , Xanthi D Andrianou  1   6 , Antonino Bella  1 , Martina Del Manso  1   7 , Massimo Fabiani  1 , Stefania Bellino  1 , Stefano Boros  1 , Alberto Mateo Urdiales  1   7 , Valentina Marziano  3 , Maria Cristina Rota  1 , Antonietta Filia  1 , Fortunato D'Ancona  1 , Andrea Siddu  1 , Ornella Punzo  1 , Filippo Trentini  3 , Giorgio Guzzetta  3 , Piero Poletti  3 , Paola Stefanelli  1 , Maria Rita Castrucci  1 , Alessandra Ciervo  1 , Corrado Di Benedetto  1 , Marco Tallon  1 , Andrea Piccioli  1 , Silvio Brusaferro  1 , Giovanni Rezza  1 , Stefano Merler  3 , Patrizio Pezzotti  1 ; COVID-19 working group  8
Collaborators, Affiliations

Epidemiological characteristics of COVID-19 cases and estimates of the reproductive numbers 1 month into the epidemic, Italy, 28 January to 31 March 2020

Flavia Riccardo et al. Euro Surveill. 2020 Dec.

Abstract

BackgroundOn 20 February 2020, a locally acquired coronavirus disease (COVID-19) case was detected in Lombardy, Italy. This was the first signal of ongoing transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the country. The number of cases in Italy increased rapidly and the country became the first in Europe to experience a SARS-CoV-2 outbreak.AimOur aim was to describe the epidemiology and transmission dynamics of the first COVID-19 cases in Italy amid ongoing control measures.MethodsWe analysed all RT-PCR-confirmed COVID-19 cases reported to the national integrated surveillance system until 31 March 2020. We provide a descriptive epidemiological summary and estimate the basic and net reproductive numbers by region.ResultsOf the 98,716 cases of COVID-19 analysed, 9,512 were healthcare workers. Of the 10,943 reported COVID-19-associated deaths (crude case fatality ratio: 11.1%) 49.5% occurred in cases older than 80 years. Male sex and age were independent risk factors for COVID-19 death. Estimates of R0 varied between 2.50 (95% confidence interval (CI): 2.18-2.83) in Tuscany and 3.00 (95% CI: 2.68-3.33) in Lazio. The net reproduction number Rt in northern regions started decreasing immediately after the first detection.ConclusionThe COVID-19 outbreak in Italy showed a clustering onset similar to the one in Wuhan, China. R0 at 2.96 in Lombardy combined with delayed detection explains the high case load and rapid geographical spread. Overall, Rt in Italian regions showed early signs of decrease, with large diversity in incidence, supporting the importance of combined non-pharmacological control measures.

Keywords: COVID-19; SARS-CoV-2; descriptive epidemiology, infectious disease modelling.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Epidemiological curves of COVID-19 cases by date of onset and date of diagnosis/sample, Italy, 28 January–31 March 2020 (n = 98,716)
Figure 2
Figure 2
COVID-19 attack rates per 100,000 population (age-adjusted) by region/AP of diagnosis (A) and number of cases by region/AP of diagnosis (n = 98,716) (B) and by municipality of residence when in the region of diagnosis (n = 93,885) (C), Italy, 28 January–31 March 2020
Figure 3
Figure 3
COVID-19 case fatality ratio by age at diagnosis and sex, Italy, 28 January–31 March 2020 (n = 10,940)
Figure 4
Figure 4
COVID-19 estimated Rt in selected Italian regions over a 7-day moving average, Italy, January 28–March 12, 2020
See this image and copyright information in PMC

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