U.S. cases have doubled in 18 days and make up one-third of all infections in the world, according to the tally.
The actual number of cases is thought to be higher, with state public health officials cautioning that shortages of trained workers and materials have limited testing capacity.
About 30% of the cases have occurred in
New York state, the epicenter of the U.S. outbreak, followed by New Jersey, Massachusetts,
California and
Pennsylvania.