The US has now tested more than 4 million people for the coronavirus, but the number of tests being done per day is plateauing

• Widespread testing is a crucial tool in curbing the coronavirus' spread and getting people back to work.
• The US initially lagged many other countries in its rate of testing per capita, but it has recently caught up.
• Around 4 million Americans have been tested, and the country is completing around 150,000 test per day.
• Visit Business Insider's homepage for more stories.

Widespread testing is one of the most important tools for fighting the coronavirus, and while the US initially lagged behind many other hard-hit countries in its per-capita testing rate, it has been catching up.

The COVID Tracking Project, an initiative run by several data scientists and journalists, has been keeping a daily count of the number of positive and negative tests for the coronavirus done in each US state, based on what state and local health agencies have reported.

On Monday, the project reported that the US passed the 4 million test mark (excluding tests whose results are still pending). About 772,000 of those tests, or 19%, came back positive.

This chart shows the total cumulative number of completed tests in the US, according to the COVID Tracking Project. That number has been steadily increasing.

The COVID Tracking Project's figures also offer a look at the daily testing rate in the US.

The number of tests done each day rose rapidly in the second half of March, and around 150,000 tests have been completed each day as of mid-April. (The large spike on April 4 came after California reported the results of around 46,000 then-pending tests.)

While testing capacity in the US is much higher than it was earlier in the pandemic, the White House's guidelines for states and cities aiming to lift strict social distancing and reopen their economies suggest that testing still needs to increase much more.

That's because safely reopening requires that health authorities track the virus' spread and plan targeted interventions in growing hotspots.

To fully "remobilize the economy" in the US, a new report from Harvard University experts suggests, the US needs to be testing 20 million people per day by mid-summer.