https://www.scientificamerican.com/article/latest-u-s-coronavirus-case-suggests-true-scope-of-undetected-spread-is-unknown/

The discovery that a California woman was likely infected with the novel coronavirus by a previously unrecognized case in her community is proof of an enormous problem the country is facing at the moment, according to public health experts. It’s clear that the virus is spreading undetected in the United States—but how broadly it’s spreading is an utter mystery.

Before Thursday, a perfect storm of problems in the Centers for Disease Control and Prevention’s development of test kits—and the agency’s reluctance to expand its recommendation of who should be tested given the limited availability of kits—meant very little testing has been done in the country. As of Wednesday, the CDC said that 445 people had been tested—a fraction of the number of tests that other countries have run.