That map shows only reported cases, ones that had been confirmed by testing. For about a week by that point, we knew that the virus had been spreading, infecting people who had no known connection to someone who had traveled internationally. The virus was out of containment.
As of noon on Thursday, the map looked like this.
The change is dramatic, with multiple states declaring emergencies as the number of cases increased. That increase was steady, day by day, and occurred across the United States.
Several of the country’s most populous states make up the bulk of the recorded cases. Washington state, New York, Massachusetts and California have about two-thirds of the recorded cases. You’ll notice a big jump in Massachusetts on March 10. That reflects cases tied to a large meeting of a biotechnology company where a participant was contagious.
In some states, the spread of the virus has been slow. Texas, for example, has added only about 30 recorded cases in the past 10 days. Florida’s rate of recorded-case growth has been similarly constrained.
Nationally, though, the increase has been dramatic. More than twice as many new cases have been reported in the past day as were recorded nationally 10 days ago. If that rate of growth is not constrained, things will get worse before they get better.