BACKGROUND: The SARS-CoV-2 infection has emerged as a rapidly spreading infection . Today it is relatively easy to isolate Covid-19 symptomatic cases, while remains problematic to control the disease spread by infected but symptom-free individuals . The control of this possible path of contagion requires drastic measures of social distancing, which imply the suspension of most activities and generate economic and social issues . This study is aimed at estimating the percentage of asymptomatic SARS-CoV-2 infection in a geographic area with relatively low incidence of Covid-19 .
METHODS: Blood serum samples from 388 healthy volunteers were analyzed for the presence of anti-SARS-CoV-2 IgG by using an ELISA assay based on recombinant viral nucleocapsid protein .
RESULTS: We found that 7 out of 388 healthy volunteers, who declared no symptoms of Covid-19, like fever, cough, fatigue etc., in the preceding 5 months, have bona fide serum anti-SARS-CoV-2 IgG, that is 1.8% of the asymptomatic population (95% confidence interval : 0.69-2.91 %).
CONCLUSIONS: The estimated range of asymptomatic individuals with anti-SARS-CoV-2 IgG should be between 26,565 and 112 , 350 . In the same geographic area, there are 4665 symptomatic diagnosed cases.