NR Coronavirus Update: Cross-State Comparisons in the U.S.

Last updated March 20, 3:30pm EST

There are now three coronavirus clusters in the U.S.: New York, California, and Washington. As of Friday afternoon, more than 7,000 New Yorkers had tested positive for the virus, while California and Washington continued to hover in the low to mid thousands. Louisiana and Florida are both on a trajectory to match those numbers in the coming weeks.

Due to the variance in testing between states, it’s hard to directly compare the severity of the three large domestic outbreaks. Washington has administered more than 20,000 tests per one million residents, compared with roughly 2,400 per million in California. As a result, there are likely many more cases in California than have been confirmed. New York, while lagging Washington, has ramped up testing in recent days, carrying out nearly 8,000 tests yesterday alone.

Likely due to that increase in testing, including drive-through testing in certain areas, New York has seen a steep increase in confirmed cases over the past few days. The five-day average growth rate of new cases in New York is 49.5 percent — a staggering figure, but, again, probably not reflective of the actual rate of transmission in the city. Today, Governor Andrew Cuomo ordered a shutdown of non-essential businesses and required that employers let non-essential workers stay home. California governor Gavin Newsom issued a similar order last night. In Washington, Governor Jay Inslee has ordered restaurants, bars, and other entertainment businesses to close their doors; limited large gatherings; and redirected medical personnel into emergency care for coronavirus patients. The growth rate of new cases in the state has leveled off in recent days.

A helpful (albeit incomplete) measure of the current severity of each cluster is the number of confirmed cases adjusted for population and testing. The chart below shows that Washington has done a much better job of controlling its outbreak than New York and California, with the caveat that the outbreak in Seattle preceded those in other states, so Washington is at a later stage in its response. We’ll be looking closely at California, which has carried out many fewer tests per capita than other states. While the California and New York clusters appear similar, we suspect that further testing will show California to be experiencing a more severe outbreak.

Note: an earlier version of this post mislabeled the y-axes.