These maps show how quickly Covid engulfed the US again

The Centers for Disease Control and Prevention (CDC) measures community transmission using two metrics — the number of cases per 100,000 people and the test positivity rate, both measured over the previous seven days.

The latest figures from the CDC show an alarming rise in the number of counties that are considered at high risk of community transmission. On Monday, 2,361 counties in the United States were listed in the “high” tier, a stark increase from 457 counties in the same tier at the beginning of July. A look at the past five weeks shows just how rapidly community transmission has increased across the country.

An area with a low transmission rate has 10 or fewer cases per 100,000 people and a positivity rate below 5%, while an area with a high transmission rate has 100 or more cases per 100,000 people and a positivity rate of 10% or higher.