coronavirus who had no symptoms infected 71 people when she took a 60-second trip in a lift on her own, according to a new study.Contact tracing experts were left baffled when trying to locate the source of an outbreak that spread across two hospitals in Heilongjiang Province, China, in mid-April.They discovered a woman, who had recently travelled to the US, was patient zero of a cluster in the province which had not reported a new Covid-19 infection in a month.The study, released by the US