Test positivity rate: How this one figure explains that the US isn’t doing enough testing yet

The U.S. has performed more coronavirus tests than any other country in the world. Yet, at the same time, the U.S. is notably underperforming in terms of suppressing COVID-19. Confirmed cases – as well as deaths – are surging in many parts of the country. Some people have argued that the increase in cases is solely due to increased testing.

I am a statistician who studies how mathematics and statistics can be used to track diseases. The claim that the increase in cases is only caused by increases in testing is just not true. But how do public health officials know this?

Testing, confirmed cases and total cases

COVID-19 testing has two purposes. The first is to confirm a diagnosis so that medical treatment can be appropriately rendered. The second is to do surveillance for tracking and disease suppression – including finding those who may be asymptomatic or only have mild symptoms – so that individuals and public health officials can take actions to slow the spread of the virus. Continue reading.