Countries that didn’t just throw up their hands and give up on contact tracing have interesting data for the rest of us.
Here’s a study of 100 Taiwanese COVID-19 patients and their 2761 “close contacts” in January-March, of whom they infected 22 (0.8%). Taiwan has a remarkably low infection rate, and did a lot of track and trace (which this study summarizes), but the government did not order Shelter In Place, but did push to boost mask production. In general, Taiwan doesn’t trust Red China, so a Taiwanese government official was monitoring chatter on a disreputable Chinese website and thus was clued in early.
Ten of 151 fellow members of the patients’ households were infected (4.6%), 5 of 76 family members who did not live in the house were infected (5.3%), 6 out of 698 health care contacts (0.9%), and 1 out of 1,836 Others (0.05%) (“Others include friends, airline crew members and passengers, and other casual contacts”). The Others were supposed to have at least 15 minutes of face to face contact within two meters:
The definition of a close contact was a person who did not wear appropriate personal protection equipment (PPE) while having face-to-face contact with a confirmed case for more than 15 minutes during the investigation period.
That only 1 out of 1836 non-family/household or non-health care traced contacts were infected seems pretty interesting from the perspective of re-opening the economy. My guess is that Taiwanese were pretty heavily masked up to keep the transmission rate that low.
Say your job was to spend 15 minutes in a row in close contact with each customer for eight hours per day. (Being a cellphone salesman might be like that.) That would be 160 customers per 40 hour week. At that rate, you’d reach your 1,836th customer during your 12th week on the job.
In contrast, at one restaurant in China on January 24 over the course of about an hour, seven diners at adjoining tables next to an infected person who had just left Wuhan. (You can’t wear a mask while eating.)
Similarly, here’s a diagram of a call center in South Korea with infected workers’ desks in blue:
That’s pretty bad.