It could be weeks before the United States can meet the demand for coronavirus testing because doctors, hospitals and some public health labs say they aren’t set up yet to do the tests.

Ratcheting up the country’s ability to detect the disease is crucial to understand how the coronavirus — now confirmed in at least 12 states — is spreading. But testing so far has been severely limited by problems with a diagnostic test developed by CDC.

The CDC has fixed its test and is working to get more test kits to labs. At the same time, the FDA has given some local labs and hospitals permission to develop their own tests. But many labs aren’t yet ready to analyze samples from patients.

FDA Commissioner Stephen Hahn said Monday that, by the end of the week, U.S. labs would have enough materials to perform close to 1 million tests. Public health experts say that figure is misleading because it is far larger than the number of samples that can be processed in labs in the coming weeks.