While the sensationalist headline is technically accurate, both the headline and the linked article bury the intent and context of the declaration. In short, don't panic.
> There have been no confirmed coronavirus cases in San Francisco to date, but as infections continue to rise across the world, “we need to allocate more resources to make sure we are prepared,” Breed said at a press conference announcing the emergency declaration.
> “To be clear, this declaration of emergency is all about preparedness. By declaring a state of emergency we are prioritizing the safety of our communities by being prepared.”
https://www.sfchronicle.com/bayarea/article/SF-mayor-London-...
> There have been no confirmed coronavirus cases in San Francisco to date, but as infections continue to rise across the world, “we need to allocate more resources to make sure we are prepared,” Breed said at a press conference announcing the emergency declaration.
> “To be clear, this declaration of emergency is all about preparedness. By declaring a state of emergency we are prioritizing the safety of our communities by being prepared.”