Life under the pall of coronavirus is rapidly becoming the new norm. Millions are now in quarantine, global stocks have plunged and supplies of toilet paper and hand gel have become prized commodities. More than 100,000 cases of Covid-19 have been officially reported around the globe. Even more sobering is that questions over the patchiness and reliability of testing may mean the real numbers are far higher.

Diagnosing Covid-19 is crucial to tracking its spread and evaluating the measures necessary to stop it. Some countries have risen to the challenge: South Korea suffered a serious early outbreak, but has tested more than 130,000 people. The picture worldwide is less promising. The US Centers for Disease Control and Prevention — which provides the aggregated US figures — had only tested 1,700 as of Sunday. Beating coronavirus will require much more comprehensive testing.

The slow US response stems from early mis-steps by the CDC. It initially restricted testing to its laboratories alone, severely limiting the numbers of samples it was possible to assess each day. That bottleneck was worsened when a problem with the design of CDC’s original tests meant that they had to be manufactured again.