San Francisco went into a second modified lockdown Saturday as COVID-19 cases surge in a city once seen as a model for fending off the virus. The City by the Bay was the first in the country to issue a shelter-in-place order in response to the virus’ arrival in the United States, but now, labeled under California’s “purple” tier indicating rapidly increasing transmission, it has instituted a 10 p.m. to 5 a.m. curfew and mandated all nonessential businesses like gyms and movie theaters to close until Dec. 21. Schools that have already reopened can remain so. Retail stores are required to cap capacity at 25 percent. Case numbers, though low relative to hotspot cities like Los Angeles and Chicago, have tripled in the past four weeks. San Francisco Mayor London Breed said, “This is the most dangerous time we've faced during this pandemic. Do not travel or gather with others.” The day before, Los Angeles issued a second stay-at-home order to all residents similar to San Francisco’s. The coronavirus’ spread is accelerating nationwide, with the confirmed case total passing 13 million Friday.