To help prevent spreading the novel coronavirus, Amazon, Google, Facebook, and Microsoft have told employees based out of the Seattle area to work from home.

Amazon is asking staff based in Seattle to work remotely until the end of March 2020. Google has more than 4,500 employees in Seattle; the company has also asked all employees to work from home.

Microsoft recommended its employees in Seattle and San Francisco to work from home through March 25th. The software giant said that it would be “continuously monitoring the situation and adjusting guidance” as appropriate.

After a contractor at its Seattle office tested positive, Facebook has closed the facility for the rest of this week. “We’ve notified our employees and are following the advice of public health officials to prioritize everyone’s health and safety,” Facebook said in a statement.

In total, 70 people in Washington state have been diagnosed with COVID-19. These include 11 people who have died.

Earlier this week, Twitter also put in place a similar policy. It said that the company “strongly” encouraged its 4,800 employees worldwide to “work from home if they’re able.”