Starting this week, everyone in Massachusetts who tests positive for the novel coronavirus should expect a phone call. The person on the other end of the line will talk them through how to quarantine and try to figure out who they might have infected. This is part of an ambitious state effort to use a public health technique called contact tracing, aimed at stopping the virus from spreading.

Contact tracing is not a new idea for combating a pandemic.

“[It] is hundreds of years old and a tried and true method,” said Emily Wroe, a physician with the global health non-profit Partners in Health, who is helping spearhead Massachusetts’ Community Tracing Collaborative.

Other places — like Singapore and South Korea — started contact tracing programs months ago, but the U.S. has lagged behind. Within the U.S., Wroe said, Massachusetts has been a pioneer.

In April, when the state’s program was first announced, “there was very little discussion that I'm aware of about contact tracing in the United States,” she said.

The idea is simple: make sure everyone who is sick or exposed to the virus does not infect anyone else.

“We are trying to do that by calling every case of COVID-19 and helping them safely isolate,” said Wroe.

The state’s small army of contact tracers, case investigators and care resource supervisors work to make sure those patients have a safe place to stay, where they won’t infect others and have access to food and any medications they need while isolated.

For this task, Wroe and her colleagues have trained a big team.

“We've had more than 30,000 applicants and we've hired more than 1,000 people,” she said, adding that the newly minted contact tracers speak more than 20 different languages.

Wroe said these are people with deep roots in their communities and demonstrated good listening and communication skills.

“They range from retired nurses to lawyers to people working in finance or the restaurant industry, to students who are off of school,” she said.

The tracers ask every person with a positive test result to name the people with whom they have come into contact recently. Wroe said this includes anyone they have been within six feet of for more than 10 or 15 minutes. Think family and friends, maybe a colleague, but not grocery store workers or passersby on the street. The tracers develop a list of all those people.

Then, the mission is “calling every contact of COVID-19 patients and letting them know about their exposure so that they can safely and effectively quarantine,” Wroe said.

Timing is key. The goal is to reach everyone before they interact with — and possibly infect — others. Wroe said the contact tracers aim to call all patients within a few hours of their positive test. And within a 48-hour window, the tracers will attempt to call all of the patient’s recent contacts. Wroe said the goal is to narrow this window down to 24 hours.

While this statewide initiative is relatively new — Wroe’s team officially comes online this week although some portion of the team has been making calls since mid-April — contact tracing has been going on in Massachusetts at the local level since the start of the pandemic. Hundreds of local boards of health across the state have done contact tracing initiatives often with the help of volunteers, but Wroe said these local efforts have not had the bandwidth to reach everyone.

With this week’s launch of the Community Tracing Collaborative, Wroe’s team is accepting cases from all over Massachusetts. The plan is for the local boards of health to continue to contact the most serious cases, including people in nursing homes and front line workers, while Wroe’s team reaches out to everyone else.

While this effort has garnered national attention, and other states have begun replicating what Massachusetts is doing, it is not without its critics.

“I tend to be somewhat on the pessimistic side about contact tracing as a general control strategy,” said Marc Lipsitch, an epidemiologist at Harvard’s School of Public Health.

“Contact tracing works well when you have relatively few cases, so that you have the resources to do it, and when you have even fewer cases that are unknown,” he said. “Neither of those is true right now in most parts of the United States.”

Lipsitch argues contact tracing requires really good testing, so that public health officials can identify all the asymptomatic cases and mild cases that can still spread the disease. He said it can work in limited settings, such as nursing homes, but it’s hard to do for a whole state, particularly at this stage in a pandemic when cases are so numerous, and testing is still so limited.

“It diverts public health effort from other activities,” he said.

Other countries that have championed contact tracing have relied on digital surveillance, especially phone apps, rather than relying on the recall and memory of interviewees.

Wroe said the Community Tracing Collaborative hopes to soon include some type of digital component to aid in their work. And, she argued, they must boost tracing capacity as testing capacity nationwide increases.