A sudden spike in new coronavirus cases in China this week shocked researchers. But the huge bump in numbers isn’t a sign that the epidemic is worsening, say researchers, it is instead the result of authorities changing how cases are confirmed. On 12 February, Hubei province reported nearly 15,000 new cases of COVID-19, the disease caused by the coronavirus, representing a 33% jump in total infections worldwide in a single day. But most of the Hubei cases — about 13,000 — are the result of a new policy in the province that means physicians can diagnose suspected cases of COVID-19 on the basis of chest images, rather than having to wait for genetic tests to confirm the presence of the virus, which can take days. The new classification was listed in updated disease reporting guidelines issued last week, only applies to Hubei, where the virus originated in the city of Wuhan.