His eyeglass frames had broken, something he cheerfully blamed on the pandemic, and he had to balance them on the bridge of his nose as he spoke.

“Once you get in someone’s space — this is going to be different, to the extent that it is virtual — but sitting with folks in their homes, the subtext of these tracings was, ‘Hey, we want to help you and your family,’” he said.

The downside of human contact tracing is that it is expensive, can overlook contacts a subject may not recall, and, some argue, is too slow for a fast-moving virus.

“Using automation to do it, cellphones and triangulations of data, that is the easiest and fastest way, and probably the most effective way to do this,” said Ranu S. Dhillon, a physician at Brigham and Women’s Hospital in Boston, who advised the government of Guinea on the Ebola outbreak.

“If you’re taking one or two days to manually figure out where someone went, you’re adding more time where people can transmit it to others,” he said.

But human outreach is a standard public health practice, first used in many countries to seek out sexual partners of men and women known to be carriers of sexually transmitted diseases.

It was gritty, solitary work. A contact tracer who worked in New Zealand in the 1970s described spending her evenings in bars and boardinghouses, tracking down subjects based on sketchy descriptions, like, “she goes to the hotel at Friday nights and she drinks Southern Comforts,” and “Kathleen — with a generous superstructure.”