We need to aggressively search for asymptomatic carriers, particularly among people who have frequent contact with the public and among vulnerable populations. This includes those who are infectious but will never develop symptoms and those who will develop them days after the test.

Those in high-risk asymptomatic groups who must be urgently targeted include health workers, especially those in long-term care facilities; the homeless and those working in shelters; grocery store employees and delivery drivers, taxi drivers, emergency workers, employees in high density workplaces like delivery warehouses and meat processing plants; and anyone who has had close contact with a known Covid-19 patient. These high-risk groups need to be tested as often as every five days, given what we know about the time it takes to develop symptoms after becoming infected, and those found to be infected should self-isolate immediately while their contacts should be quarantined for 14 days.