Testing for Covid-19 infections and a fast turnaround for results are critical for controlling the pandemic, but broad-based population tests are not always useful, officials at the World Health Organization said on Thursday.

Maria Van Kerkhove, a WHO epidemiologist, said the UN agency recommended suspected cases be tested and their contacts, if feasible, likewise, but the focus should be on people with symptoms.

Mike Ryan, head of its emergencies programme, noted that broad population testing programmes absorbed a large amount of resources.

The comments come after the U.S. Centers for Disease Control and Prevention (CDC) said this week that people exposed to Covid-19 but not symptomatic may not need to be tested, surprising doctors and politicians and prompting accusations the guidance was politically motivated.