Mass tests and their limits

Mass testing took place this weekend in the canton of Graubünden. The tests revealed around 1% of positive cases. "This small figure is a bit like looking for a needle in a haystack. It's about one person in 100, whereas with the usual system of symptomatic people, it's one person in seven. It's an enormous amount of energy to catch very few people, most of whom aren't necessarily infectious because they have very small viral loads."