Testing Times?

There is a report (although it is a single study and urgently needs repeating) from the University of Padua where all 3,300 residents of the small town of Vo were tested twice for Covid-19 (https://www.theguardian.com/world/2020/mar/18/scientists-say-mass-tests-in-italian-town-have-halted-covid-19). There were initially 90 people with the condition in the town but this has, with management of contacts been currently reduced to zero. The really important observation, however, is that 6 asymptomatic people were identified. If they had not been found, they could have innocently infected the people around them, making controlling the pandemic very difficult. This strongly suggests that mass screenings for infection (and not just clearly ill people, in hospitals) will be necessary if this virus condition is to be eradicated. Just how common are asymptomatic people?