The US government is fighting to contain and slow down the spread of the coronavirus. Testing is central to these efforts. Molecular biologist and viral researcher Maureen Ferran answers some basic questions about how these diagnostic tests work—and if there are enough to go around.

Who gets tested for the virus?

Currently there are two main reasons someone would be tested for the coronavirus: having symptoms or exposure to an infected person.

The main symptoms of COVID-19, the disease caused by the coronavirus SARS-CoV-2, are fever, dry cough, and shortness of breath. These look a lot like the flu and the common cold, so it takes a physician to determine if testing for the virus is necessary.

Initially, the Centers for Disease Control and Prevention recommended testing only people with symptoms and who had potentially been exposed to the virus. But to the surprise of public health officials, several of the first people in the US who tested positive for the virus had no obvious exposure. This development suggested that the virus was being transmitted locally, meaning it was spreading from person to person easily and/or that people may have been transmitting the virus without experiencing serious symptoms.