The spread of the novel coronavirus is doing for tech firms what no other argument for remote work apparently could, as Google, Facebook, and others are asking employees to stay home while they do their jobs.

Those policies are looking ever more like sensible precautions, as this week Amazon has confirmed that an employee based in Seattle tested positive for the virus. The employee apparently went home feeling sick on February 25 and has not returned to the office since. Two Amazon employees based in Italy also are confirmed to have contracted the virus.

Washington state's King County—home to Seattle and its tech-heavy suburbs Kirkland, Redmond, and Bellevue—is the site of the biggest US outbreak of COVID-19 so far. Microsoft, which is also based in the Seattle area, is now allowing employees based in its Seattle or San Francisco offices to work remotely through at least March 9.

(Update: A few hours after we published our story, Microsoft amended its policy and notified all employees in the Seattle and San Francisco areas that they should work from home if they are able through March 25.)

Google, which has tended not to support telework on a large scale in the past, ordered most of the 8,000 employees based in its Dublin office to stay home and work remotely this week after an employee reported "flu-like symptoms" on Monday.

Twitter, too, went big on telework this week in light of COVID-19, "strongly encouraging" all its employees globally to work from home if they are able and mandating that employees in Hong Kong, Japan, and South Korea do so. And Facebook, in addition to canceling its F8 developer conference, has reportedly told employees they can work from home without seeking managerial approval.

The virus was first spotted in Wuhan in January. By the end of that month, Chinese authorities prohibited travel to or from Wuhan and several nearby cities. Americans who were repatriated from Wuhan amid the outbreak were put in quarantine, but the disease has been able to spread—albeit more slowly, so far—throughout the United States, Europe, and Asia nonetheless.

Large companies, including major tech firms, likewise first restricted travel to or from China for their employees, later expanding their travel restrictions. This week, Google halted all international travel for its employees, along with canceling its I/O developer conference, slated for May.