There are deep concerns laboratory tests are incorrectly telling people they are free of the coronavirus.
Stories in several countries suggest people are having up to six negative results before finally being diagnosed.
Meanwhile, officials in the epicentre of the epidemic, Hubei province, China, have started counting people with symptoms rather than using the tests for final confirmation.
As a result, nearly 15,000 new cases were reported on a single day – a quarter of all cases in this epidemic.
What are these tests and is there a problem with them?
They work by looking for the genetic code of the virus.
A sample is taken from the patient. Then, in the laboratory, the virus’s genetic code (if it’s there) is extracted and repeatedly copied, making tiny quantities vast