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On 21 February 2020, a resident of the municipality of Vo', a small town near Padua (Italy), died of pneumonia due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection1. This was the first coronavirus disease 19 (COVID-19)-related death detected in Italy since the detection of SARS-CoV-2 in the Chinese city of Wuhan, Hubei province2. In response, the regional authorities imposed the lockdown of the whole municipality for 14 days3. Here we collected information on the demography, clinical presentation, hospitalization, contact network and the presence of SARS-CoV-2 infection in nasopharyngeal swabs for 85.9% and 71.5% of the population of Vo' at two consecutive time points. From the first survey, which was conducted around the time the town lockdown started, we found a prevalence of infection of 2.6% (95% confidence interval (CI): 2.1-3.3%). From the second survey, which was conducted at the end of the lockdown, we found a prevalence of 1.2% (95% CI: 0.8-1.8%). Notably, 42.5% (95% CI: 31.5-54.6%) of the confirmed SARS-CoV-2 infections detected across the two surveys were asymptomatic (that is, did not have symptoms at the time of swab testing and did not develop symptoms afterwards). The mean serial interval was 7.2 days (95% CI: 5.9-9.6). We found no statistically significant difference in the viral load of symptomatic versus asymptomatic infections (P = 0.62 and 0.74 for E and RdRp genes, respectively, exact Wilcoxon-Mann-Whitney test). This study sheds light on the frequency of asymptomatic SARS-CoV-2 infection, their infectivity (as measured by the viral load) and provides insights into its transmission dynamics and the efficacy of the implemented control measures.

Original publication

DOI

10.1038/s41586-020-2488-1

Type

Journal article

Journal

Nature

Publication Date

08/2020

Volume

584

Pages

425 - 429

Addresses

Department of Molecular Medicine, University of Padova, Padua, Italy.

Keywords

Imperial College COVID-19 Response Team, Imperial College COVID-19 Response Team, Humans, Pneumonia, Viral, Coronavirus Infections, Viral Nonstructural Proteins, Viral Envelope Proteins, Viral Load, Prevalence, Disease Outbreaks, Adolescent, Adult, Aged, Aged, 80 and over, Middle Aged, Child, Child, Preschool, Infant, Infant, Newborn, Italy, Female, Male, Young Adult, Asymptomatic Infections, Pandemics, Betacoronavirus, RNA-Dependent RNA Polymerase, COVID-19, SARS-CoV-2, Coronavirus Envelope Proteins, Coronavirus RNA-Dependent RNA Polymerase