The coronavirus outbreak in the Seattle area is at a critical juncture and could see explosive growth in cases much like Wuhan, China, if public officials don’t take immediate, forceful measures, according to a new analysis of genetic data.

The author of the analysis, a computational biologist named Trevor Bedford, said there are likely already at least 500 to 600 cases of Covid-19 in the greater Seattle area. He urged health authorities and the public to immediately begin adopting non-pharmaceutical interventions — imposing “social distancing4” measures, telling the sick to isolate themselves, and limiting attendance at large gatherings.

“Now would be the time to act,” Bedford, who is at the Fred Hutchinson Cancer Research Center in Seattle, told STAT.