California’s new case rate has remained high in California this month as Golden State’s total number of cases has surpassed New York’s, making it the state with the best-known coronavirus infections of all in the United States.
Average new cases have flattened slightly in the past two weeks, after growing rapidly in previous weeks. To see where the virus is spreading, we calculated the rate of new cases in each county, the number of cases reported in the previous 14 days per 10,000 residents, then mapped that data over time. The animated map shows how, and when, the coronavirus spread through California from April 1 to July 23.
In early April, the virus was most prevalent in Bay Area and Southern California counties, then became more concentrated in Los Angeles and Imperial counties by the end of the month, spurred by widespread community transmission. In May, the virus spread more across the state, as large outbreaks in prisons caused spikes in Santa Barbara and Kings County.
In June, the virus took hold most strongly in many parts of Southern California and the Central Valley, and has continued to spread rapidly from late June to mid-July.
As of April 1, only 12 counties had a rate of more than 2.5 cases per 10,000 residents in the previous 14 days. As of June 1, 26 counties had a new high case rate, and by July 9, almost all counties, 53 of 58, had a new case rate greater than 2.5. Two weeks later, on July 23, only 3 counties had a case rate below the 2.5 threshold.
While the state has dramatically increased testing for the coronavirus, that does not fully explain the increasing rate of infections. According to the California Department of Public Health, the positivity rate of the 7-day test, which they call “a key indicator of community spread,” tends to rise and has once again reached the positivity rate threshold. 8% used by the state. The 7-day positivity rate in an individual county is a factor used to determine if the county is on the state’s monitoring list that determines the degree of reopening allowed. The state’s positive testing rate started high when the tests were rationed in March and April, but remained between 4 and 6% for most of May and June, before trending upward in July, topping 8% in mid-July and again on July 23)
The map shows that California’s early order to stay at home likely saved the state from the early exponential growth seen in places like Italy and New York. But while the Golden State kept the curve in check for many weeks, the trend lines have become steeper and worse this month. Now the number of new cases has stabilized, and only time will tell if it’s a sign of a downward trend or just a temporary slowdown.
Find more data on coronavirus cases, hospitalizations, and deaths in the Bay Area and elsewhere in California with our coronavirus tracker
