Abstract
Early in the COVID-19 pandemic, asymptomatic transmission represented an important challenge for controlling the spread of SARS-CoV-2 through the traditional public health strategies. Further understanding of the contribution of asymptomatic infections to SARS-CoV-2 transmission has been of crucial importance for pandemic control. We conducted a retrospective epidemiological study to characterize asymptomatic COVID-19 cases occurred in the Apulia region, Italy, during the first epidemic wave of COVID-19 outbreak (February 29-July 7, 2020). We analyzed data collected in a regional platform developed to manage surveillance activities, namely, investigation and follow-up of cases and contacts, contact tracing, and laboratory and clinical data collection. We included all asymptomatic cases that were laboratory-confirmed during the appropriate follow-up, defined as persons infected with SARS-CoV-2 who did not develop symptoms/clinical signs of the disease. Between February 29 and July 7, 2020, a total of 4,536 cases were diagnosed with COVID-19 among 193,757 tests performed. The group of persons with asymptomatic SARS-CoV-2 infection consisted of 903 cases; the asymptomatic proportion was 19.9% (95% CI: 18.8-21.1%); this decreased with increasing age (OR: 0.89, 95% CI: 0.83-0.96; p = 0.001), in individuals with underlying comorbidities (OR: 0.55, 95% CI: 0.41-0.73; p < 0.001), and in males (OR: 0.69, 95% CI: 0.54-0.87; p = 0.002). The median asymptomatic SARS-CoV-2 RNA positive period was 19 days (IQR: 14-31) and the cumulative proportion of persons with resolution of infection 14 days after the first positive PCR test was 74%. As the public health community is debating the question of whether asymptomatic and late spreaders could sustain virus transmission in the communities, such cases present unique opportunities to gain insight into SARS-CoV-2 adaptation to human host. This has important implications for future COVID-19 surveillance and prevention.
Highlights
SARS-CoV-2 is a novel coronavirus causing the current pandemic [1], which has resulted in millions of infections and hundreds of thousands of deaths worldwide
The asymptomatic proportion was defined as the proportion of infected individuals who were never symptomatic for COVID-19 among the total number of infected individuals [15]
Our results showed that asymptomatic infections were more common in young individuals without underlying diseases and among females
Summary
SARS-CoV-2 is a novel coronavirus causing the current pandemic [1], which has resulted in millions of infections and hundreds of thousands of deaths worldwide. A total of 11,500,302 coronavirus disease 2019 (COVID-19) cases were diagnosed in the world during the initial wave of the epidemic (as of July 7, 2020). 137 days since the first confirmed COVID-19 case was announced, Italy was the eleventh most affected country, with 241,819 total cases and 34,869 deaths [2], mainly concentrated in the Northern area of the country, in Lombardy, Piedmont, BioMed Research International. The clinical outcomes of SARS-CoV-2 vary from asymptomatic infection to a mild-to-severe or critical disease [5, 6]. The proportion of asymptomatic infection could be estimated to be 10.1-23.0% of all confirmed cases before May 2020 [8]. It was reported that asymptomatic infections were more common in middle-aged individuals in Shenzhen (median age: 49 years; 30.9% between 30 and 49 years) and a few younger people in Nanjing (median age: 32.5 years) [9]
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