Covid-19: does more testing always mean more cases?

Since the beginning of the pandemic, ‘test, test, test’ has been the key message from epidemiologists, infectious disease specialists and healthcare professionals alike. But how does a country know if it’s doing sufficient testing? Or that it’s catching enough of the asymptomatic cases? Nicola Davis speaks to Prof Rowland Kao about the positivity rate, a value that can help to answer some of these difficult questions. Help support our independent journalism at